CA1243606A - Pharmaceutical compositions containing iron complexes of 3-hydroxy-4-pyrones - Google Patents

Abstract

ABSTRACT

Pharmaceutical compositions containing an iron complex of 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, are of value for the treatment of iron deficiency anaemia.

Description

3~i~6 122]56tl PHARMACEUTICAL COMPOSITIONS CONTAINING

-This invention relates to iron compounds for use in pharma-ceutical compositions for the treatment of iron defieiency anaemia.
An adequate supply of iron to the body i5 an essential require-ment for tissue growth in both man and animals. ~lthough there is 05 normally an ample amount of iron in the diet~ the level of absorption of iron from food is generally low so that the supply of iron to the body can easily become critical under a variety of conditions.
Iron deficiency anaemia is commonly encountered in pregnancy and may also present a problem in the newly born, particularly in certain animal species such as the pig. Moreover, in certain pathological conditions there is a maldistribution of body iron leading to a state of chronic anaemia. This is seen in chronic diseases such as rheumatoid arthritis, cer~ain haemolytic diseases and cancer.
Although a wide range of iron compounds is already marketed for the treatment of iron deficiency anaemia, the level of iron uptake by the body from these compounds is often quite low thPreby necessitating the administration of relatively high dosage levels of the compound. The administration of high dose, poorly absorbed, iron complexes may cause siderosis of ~he gut wall and a variety of side effects such as nausea, vomiting, constipation and heavy malodorous stools The present invention and that of the copending divisional application relate to a group of hydroxypyrone iron complexes which we have identified as being of particular value for use at relatively low dosage levels in the treatment of iron deficiency anaemia. The hitherto unrecognised value of these complexes in such a conte~t, as shown by in vivo experiments, is unexpected in view of the well known need for improved iron compounds for the '' . .
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treatment of iron deficiency anaemia and the known ability of such hydroxypyrones to form iron complexes. Furthermore, several of these compounds have previously been used in foodstuffs thereby indicating their non-toxic nature and the consequent suitability 05 for pharrnaceutical use of the;r iron complexes.
Although iron complexes of certain of the compounds have themselves also previously been proposed for use in foodstuffs, as colouring agents, it had never previously been appreciated that they have any therapeutic use and the conditions proposed for the use of such complexes as colouring agents would not generally be such as to lead to any significant physiological effect. Moreover, the iron complexes proposed for this use were not neutral 3:1 hydroxypyrone:iron(III) complexes such as are the preferred complexes of the present invention and that of the divisional application.
According to the present invention a process for preparing a medicament for effecting an increase in the amount of iron in the bloodstream of a patient comprises incorporating therein as an active ingredient an iron complex of 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms is replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms.
The iron complexes of use in the present invention preferably contain iron in the ferric state. Although the use of complexes containing iron in the ferrous state may be considered, such complexes tend to be less stable and are thus of less interest.
The iron complexes are preferably neutral and this is conveniently achieved by complexing with the iron cation the appropriate number of anions derived from the hydroxypyrone (through the conversion OH --~ O~) necessary to produce neutrality. Preferred iron complexes of use in the present invention are thus of the 3:1 form, containing three hydroxypyrone anions complexed with a ferric cation.

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The substituted 3-hydroxy-4-pyrones may carry more than one type of aliphatic hydrocarbon group but this is not usual and, indeed, substitution by one rather than two or three aliphatic hydrocarbon groups is preferred. The term aliphatic hydrocarbon 05 group is used herein to include both acyclic and cyclic groups which may be unsaturated or saturated, the acyclic groups having a branched chain or especially a straight chain. Groups of from 1 to 4 carbon atoms and particularly of 1 to 3 carbon atcms are of most interest. Saturated aliphatic hydrocarbon groups are preferred, these being either cyclic groups such as the cycloalkyl groups cyclopropyl and especially cyclohexyl or, more particularly, acyclic groups such as the alkyl groups n-propyl and isopropyl, and especially ethyl and methyl. Substitution at the 2- or 6-position is of especial interest although, when the ring is substituted by the larger aliphatic hydrocarbon groups, there may be an advantage in avoiding substitution on a carbon atom alpha to the -C-C
O OH
system. This system is involved in the complexing with iron and the close proximity of one of the larger aliphatic hydrocarbon groups may lead to steric effects which inhibit complex formation.
Examples of specifio compounds whose iron complexes are of use in the present invention are shown by the following formulae ~I), (II) and (III):-O O O
UO~ R/~`~l 1R

(I) (II) (III) in which R is a cycloalkyl or alkyl group, for example methyl, ethyl, n-propyl or isopropyl. Among these compounds 3-hydroxy-2 methyl-4-pyrone (maltol; II, R = CH3) is most interest, whilst 3-hydroxy-4-pyrone (pyromeconic acid; I), 3-hy~roxy-6-methyl-~-pyrone (III, R = CH3) and particularly 2-ethyl-3-hydroxy-4-pyrone (ethylpyromeconic acid; II, R = C2Hs) are also of especial interest. For convenience the compound 3-hydroxy-2-methyl~~-pyrone 05 is referred to 1n the followin~ d;scussion under the name ma'l~o'l.
In the case of certain of the hydroxypyrones referred to above, i.e. maltol, 3-hydroxy-6--methyl-4-pyrone and 2-ethyl-3-hydroxy-4-pyrone, the formation of an iron complex of the compound has been referred to in the literature, although the only 3:1 complex reported is that of maltol.
The iron complexes are conveniently prepared by the reaction of the hydroxypyrone and ferric ions, the latter conveniently being derived from a ferric salt, particularly a ferric halide and especially ferric chloride. The reaction is conveniently effected in a suitable mutual solvent and water may often be used for this purpose. If desired, however, an aqueous/organic solvent mixture may be used or an organic solvent, for example ethanol, methanol or chloroform and mixtures of these solvents together and/or with water where appropriate. In particular, methanol or especially ethanol may be used where it is desired to effect the separation of at least a major part of a by-product such as sodium chloride by precipitation whilst the iron complex is retained in solution.
It should be appreciated that the nature of the iron complex obtained by the reaction of a hydroxypyrone and iron ions will depend both on the proportion of these two reactants and upon the pH of the reaction medium. Thus, for the preparation of the 3:1 ferric complex, for example, ~he hydroxypyrone and the ferric salt are conveniently mixed in solution in a 3:1 molar proportion and the pH adjusted to a value in the range of 6 to 9, for example 7 or 8. If a similar excess of hydroxypyrone:iron is employed but no adjustment is made of the acidic pH which results on the admixture of the hydroxypyrone and an iron salt such as ferric chloride, then a mixture of the 2:1 and l:l complex will instead be obtained.

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Reaction to form the iron complex is generally rapid and will usually have proceeded substantially to completion after 5 minutes at about 20C, although a longer reaction time may be used if necessary. Followin~ separation of any precipitated by-product7 05 such as sodium chloride in the case of certain solvent systems, the reaction mixture may conveniently be evaporated on a rotary evaporator or free~e dried to yield the solid iron complex. This may, if desired, be crystallised from a suitable solvent, for example water, an alcohol such as ethanol, or a solvent mixture, including mixtures containing an ether.
Whilst for some uses it may be appropriate to prepare the iron complex in substantially pure form, i.e. substantially free from by-products of manufacture, in other cases, for example with - a solid oral formulation as described hereinafter, the presence of by-products such as sodium chloride may be quite acceptable. In general, however, the neutral 3:l hydroxypyrone:iron (III) complex is of particular interest in a form which is substantially free at least from those by-products which are complexes containing different proportions of hydroxypyrone and iron, in particular the 2:1 and l:l complexes. As indicated hereinafter, it may be advantageous under some circumstances for the iron complex to be used in admixture with the free pyrone or a salt thereof containing a physiologically acceptable cation. It is possible to produce such a mixture by mixing the two components either in the solid form or in solution, followed by isolation of a solid mixture in the latter case when a solid composition is required. However, it may be more convenient to obtain such a mixture by reacting a molar proport~on of the hydroxypyrone and ferric ions of 8reater than 3:1. It should be stressed, however, that the conditions as well as the proportion of reactants used in the reaction are of importance if a mixture of the free pyrone and the preferred neutral 3:] complex is to be obtained. In particulari as indicated previously, the pH of the reaction mixture is particularly important and, because of this fact, certain prior art procedures concerned ~? `

with the use of iron hydroxypyrone complexes in food colour;ng, for example as described in US patent 4,018,907, substan-tially fail to yield the 3:1 cornplex even though an excess of the hydroxypyrone is present, owing to the lack of pH control.
05 Certain hydroxypyrones, such as maltol, are available commercially. With others, a convenient startiny material in many instances consists of 3-hydroxy-4 pyrone which is readily obtainable by the decarboxyla-tion of 2,6-dicarboxy-3-hydroxy-4-pyrone (meconic acid). Thus, for example, 3-hydroxy-4-pyrone may be reacted with an aldehyde to insert a l-hydroxyalkyl group at the 2-position, which group may then be reduced to produce a

2-alkyl-3-hydroxy-4-pyrone. The preparation of 2-ethyl-3-hydroxy-4-pyrone, etc., by this route is described in the published US application serial number 310,141 (series of 19~0).
It will be appreciated that these are not the only routes available to these compounds and their iron complexes and that various alternatives may be used as will be apparent to those skilled in the art.
The iron complexes such as that of 3-hydroxy-2-methyl-4-pyrone may be formulated with a physiologically acceptable diluent or carrier for use as pharmaceuticals for veterinary or human use in a variety of ways. The iron complexes may be applied as an aqueous, oily or emulsified composition incorporating a liquid diluent, which will, however, most usually be employed for parenteral administration and therefore may conveniently be sterile and pyrogen free. One form of composition of particular interest thus has the form of a sterile, injectable solution, suspension or ~L2~L3K~;

emulsion. Oral administration is, however, more generally to be preferred for the treatment of iron deficiency anaemia in humans and the complexes of the present invention may be given by such a route. Although compositions incorporating ~ liquid diluent may 05 be used for oral administration, it is preerred to use compositions incorporating a solid carrier, for example a conventional solid carrier material such as starch, lactose, dextrin or magnesium stearate. The iron complex will of course be present in such a preferred composition in solid form, which form is accordingly a preferred one for the complex, and such a solid composition may conveniently be presented as some type of formed composition, for example, as tablets, capsules (including spansules), etc.
Although solid compositions are preferred in many applications, liquid compositions are of interest in certain particular instances, for example human and veterinary intramuscular administration and veterinary oral administration as discussed hereinafter. It is often desirable to produce liquid compositions containing a higher concentration than ;s readily obtainable with a purely aqueous composition and it has been found that this may be done by the use of glycols or glycol ethers, either in admixture with water or, for better solubilisation, alone. The glycol ethers of particular in~erest are the mono-ethers containing as an etherifying group an aliphatic hydrocarbon group of ] to 6 carbon atoms as described above, for example a methyl group, such a glycol mono-ether being methyl ethylene glycol. In general, however, the glycols themselves are preferred. Examples of such glycols are the simple dihydroxy alkanes such as ethylene glycol as well as those more complex compounds comprising two hydroxy groups attached to a chain containing both carbon and oxygen atoms, such as triethylene glycol, tetraethylene glycol and polyethylene glycol, for example of 4,000 dalton~ ~olecular weight. Triethylene glycol and especially tetraethylene glycol are of particular interest in view of their Yery low toxicity. By using such glycols and glycol ethers it is poss~ible to increase solubility for many complexes to 10 to ~0 mg/ml.

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~2'~3~6 In the case of animals, compositions for parenteral adminis-tration are of greater interest than with humans. The problems of iron deficiency anaemia in newly born pigs arise primarily during the first three weeks or so of their life when a very rapid wei~ht 05 gain takes place. The usual routes for administration o the iron complexes of the present invention to young piglets are parenteral, for example intramuscular, or oral, for example as a liquid preparation "injected" into the mouth. However, an alternative approach is to enhance the iron content of the milk on which the piglets are feeding by treating the mother pig using oral or parenteral administration9 for example with an injectable slow release preparation (such an approach may also be an interest in a human context). When it is applicable to feed piglets on foodstuffs other than the milk of the mother pig, it may also be possible to effect the pharmaceutical administration of the iron complex in this other foodstuff.
Other forms of administration than by injection or through the oral route may also be considered in both human and veterinary contexts, for example the use of suppositories for human admini-stration.
Compositions may be formulated in unit dosage form, i.e. inthe form of discrete portions containing a unit dose, or a multiple or sub-unit dose. Whilst the dosage of hydroxypyrone iron complex given will depend on various factors, it may be stated by way of guidance that maintenance at a satisfactory level of the amount of iron present in the human body will often be achieved using a daily dosage, in terms of the iron content of the compound, which lies in a range from about O.l to lOO mg and often in a range from 0.5 to l0 mg, for example I or 2 mg, veterinary doses being on a similar g/kg body weight ratio. However, it will be apppreciated that it may be appropriate under certain circ~n-stances to give daily dosages either below or above these levels.
In general, the aim should be to provide the amount of iron required by the patient wit~out administering any undue excess and the ..~ j . ~

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~3;~6 g properties of the pharmaceutical compositions according to the present invention are particularly suited to the achievement of this aim. Sim-ilarly, the concentration of iron in the pharmaceutical composition ;n the form o-F the hydroxypyrone complex 05 may vary quite widely, for example over a range Fro~ 0.01 to 20% w/w. However, it is more usual for the concentrat;on to exceed 0.01% w/w and it may often exceed 0.05 or 0.1% w/w.
A common range of concentration is 0.05 to 5% w/w, for example 0.2 to 0.5, 1 or 2% w/w.
The present invention thus includes a pharmaceutical composition comprising a physiologically effective amount of the neutral 3;1 hydroxypyrone:iron(III) complex of 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, together with a physiologically acceptable diluent or carrier but excluding any liquid which is not sterile and pyrogen free.
Where desired, another hydroxypyrone iron complex as described above may be present in the pharmaceutical composition in addition to that of 3-hydroxy-2-methyl-4-pyrone or indeed other active compounds may be included in the composition, for example compounds having the ability to facilitate the treatment of anaemia, such as folic acid. Another additional component which may be included in the composition, if desired, is a source of zinc. Iron compounds used in the treatment of iron deficiency anaemia can inhibit the mechanism of zinc uptake in the body and this can cause serious side effects in the foetus when treating anaemia in a pregnant female. It is believed~ however, that the iron complexes of the present invention have a further advantage in that they either do not have this effect or exhibit the effect at a lower level than the compounds at present used in the treatment of anaemia.
Accordingly, it may often be the case that the level of zinc providing compound added to the composition may not require to be high or, with preferred formulations of the iron complexes, may be dispensed with altogether.

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, - 9a -We have Found that the iron complexes of the present invention are particularly suited to the treatment of iron deficiency anaemia, both in humans and also in a veterinary context and particularly for the treatment of various mammalian species, 05 especially p;gs. Thus, -the chelat~ng agents which they contain, ., ~.

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-- ]o --and particularly maltol, have a high affinity for iron (log ~3 = 30 for maltol) but a lower affinity for copper (II), zinc (II), calcium and magnesium. Both the high a~inity of maltol for iron and its low affinity for calcium are reflected 05 in its KSol value ~log K l is defined as being equal to log ~Fe(L)n ~ 21 - [pKsp ~ n log aL(H~) ~ m log aL(Ca~ )] where log ~Fe(L)n is the cumulative affinity constant of the ligand in question for iron (III), pK is the negative logarithm of the solubility product for Fe(OH)3 and has a value of 39, n and m are the number of hydrogen and calcium ions, respectively, which are bound to the li~and, and aL(H~) and aL(Ca++) are the affinities of the ligand for hydrogen ions and calcium ions, respectively~. In order to solubilise iron (III) hydroxide, log K l must be greater than 0. The value of K for maltol is 8.0 and this is also sol sufficiently large to prevent appreciable competition from phytate, phosphate, thiols and other potential ligands likely to occur in the intestinal lumen. In order to exchange iron efficiently with transferrin, the log KSol value should be close to that of apotransferrin, which is 6.0, so that maltol is also suitable in this respect. Moreover, although the neutral 3:1 maltol:iron (III) complex is thermodynamically stable (thermodynamic stability constant = 30) it is also extremely labile and is therefore able to donate iron to high affinity sites, such as those found in apotransferrin. The half life for the exchange of iron (III) between the maltol complex and apotransferrin is ] minute w~ereas, by contrast, the corresponding figure for the complex of EDTA with iron (III) is 4 days.
It will be appreciated, however, that in addition to possessing properties SUCil as those described a~ove for iron maltol, a compound which is to act as a source of iron through oral administration is required to to show a high level of membrane permeability. An indication of the properties of a compound in this respect is provided by the value of the partition coefficient (K t) obt~ined 36~
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on partition between n-octanol and Tris hydrochloride (20 mM, pH 7.4; Tris representing 2-amino-2-hydroxymethylpropane, 1,3-diol) at 200C and expressed as the ratio ~concentration o~
compound in oryanic phase)/~concentration of compound in aqueous 05 phase). The value of Kpart for the neutral 3:1 maltol:iron(III) complex is 0.5, which is well placed in the preferred range of 0.2 to 1.0 and compares favourably with the figures of 0.001 ` and 0.0015 for the EDTA:iron(III) complex and iron(III) ascorbate, respectively.
10The value of the iron complexes of the present invention is confirmed by various 7n vitro and in vivo tests. Thus, their ability to permeate biological membranes is confirmed in practice by tests of the ability of the 59Fe labelled iron complexes to permeate erythrocytes. Moreover, these iron complexes have been found to exhibit a high level of efficiency in promoting iron uptake, as measured in the rat small intestine, as compared with a range of other iron complexes currently marketed for the treatment of iron deficiency anaemia. In vivo experiments in the cat and rat have confirmed the value of iron maltol compounds as a source of iron, the iron uptake obtained either on intravenous administration `or on direct administration into the samll intestine being markedly superior to that obtained with commercially available iron compounds such as iron sulphate, iron EOTA and iron gluconate. It was found from these experiments that the iron was not excreted to any significant extent in the urine but became generally distributed throughout the body, the complexes d~nating iron to transferrin to an equilibrium level once they are present in the bloodstream.
Certain aspects of their formulation may enhance the activity of the complexes in particular contexts. Thus, although the neutral 3:1 ferric complexes are stable over a wide pH range from about 4 or 5 up to 10, they will dissociate at the pH values of less than 4 prevailing in the stomach to form a mixture of the 2:1 and 1:1 complex together ~ith the free hydroxypyrone, and it has been found that the blood levels of 59Fe achieved on administration ~. ..

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of the 3:1 co~plex into the small intestine are much higber than when administration is made into the stomach. However, when the stomach contents is flushed to the small intestine in in vivo cat experiments an increase of iron uptake occurs almost immediately.
05 The undesirable effects o~ this dissocia~ion on iron uptake may he countered by using one or more of the following procedures in the formulation of the iron complex. Firstly, one of several variations may be employed which avoid or reduce exposure of the iron complex to the acidic conditions of the stomach. Such approaches may range from a controlled release system, for example one based upon a polymer, which simply provides a delayed release of the complex with time, through a system which is resistant to dissociation under acidic conditions, for example by the use of buffering, to a system which and is biased towards release under conditions such as prevail in the small intestine, for example a pH sensitive system which is stabilised towards a pH of 1 to 3 such as prevails in the stomach but not one of 7 to 9 such as prevails in the small intestine. Since the pH
of the stomach is higher after a meal, it may be advantageous, whatever method of formulation is used, to administer the iron complexes at such a time.
~ particularly convenient approach to a controlled release composition involves encapsulating the iron complex by a material which is resistant to dissociation in the stomach but which is adapted towards dissociation in the small intestine (or possibly, i~ the dissociation is slow, in the large intestine). Such encapsulation may be achieved with liposomes, phospholipids generally being resistant to dissociation under acidic conditions.
The liposomally entrapped 3:1 iron(III) complexes can therefore survive the acid environment of the stomach without dissociating to the 2:1 and ~:] complexes, and the free hydroxypyrone. On entry into the small intestine, the pancreatic enzymes rapidly destroy the phospholipid-dependent structure of the liposomes thereby releasing the 3:l complex. Liposome disruption is further ~acilitated by the presence of bile salts. However, it is usually , ~..

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more convenient to effect the encapsulation, including micro-encapsulation, by the use of a solid composition of a pH sensitive nature.
The preparation of solid compositions adapted to re0ist 05 dissociation under acidic conditions but adapted towards dissoci-ation under non-acidic conditions is well known in the art and most often involves the use of enteric coating, whereby tablets, capsules, etc, or the inidividual particles or granules contained therein, are coated with a suitable material. Such procedures are described, for example, in the article entitled "Production of enteric coated capsules" by Jones in Manufacturing Chemist and Aerosol News, May 1970, and in such standard reference books as "Pharmaceutical Dosage Forms, Volume III by Liebermann and Lackmann (published by Marcel Decker). One particular method of encapsulation involves the ~Ise of gelatine capsules coated with a cellulose acetate phthalate/ diethylphthalate layer. This coating protects the gelatin capsule from the action of water under the acid conditions of the stomach where the coating is protonated and therefore stable. The coating is however destabilised under the neutral/
alkaline conditions of the intestine ~here it is not protonated, thereby allowing water to act on the gelatin. Once released in the intestine the rate of permeation of the intestine wall by the water soluble 3:~ iron~III) complex is relatively constant irrespec-tive of the position within the intestine, i.e. whether in the jejunum, ileum or large intestine. Other examples of methods of formulation which may be used include the use of polymeric hy~rogel formulations which do not actually encapsulate the iron complex but which are resistant to dissociation under acidic conditions.
A second approach to countering the effect of the acidic conditions prevailing in the stomach involves formulation of the comple~ in the pharmaceutical composition ~ogether with the metal-free hydroxypyrone from ~hich it is derived or a salt thereof containing a physiologically acceptable cation. The dissociation of the neutral 3:1 ferric complex involves various equilibria between this complex, the 2:l and l:l complexes, and the metal-free compound, so that the presence of the latter will inhibit : .. ~........................ ..
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- ]4 -this dissociation. Any proportion of the free compound can be advantageous in this context but little further advantage accrues from increasing the proportion beyond a certain level. A preferred range for the molar proportion of the free compound present in 05 compositions according to the present invention i8 thus from 0 to ]00 moles of free hydroxypyrone:l mole of iron comple~.
Conveniently, a proportion of up to no more than 20, 30 or 50 moles:] mole is used with a lower level of I or 2 moles:] ~ole, although to obtain a marked effect upon dissociation of the iron complex a proportion of at least 5 or l0 moles:~ mole is usually employed. Thus a range of particular interest for the molar proportion of uncomplexed hydroxypyrone:iron complex is from l:l to l00:~, for example from 5:l to 50:~ or from ]0;1 to 20:l. It will be appreciated that a solid mixture of the hydroxypyrone and the corresponding 3:l iron(III) complex in a proportion of from l:l to lO0:] is novel and that the use of such a mixture is an important feature of the present invention since in principle it can enable one to obtain almost quantitative uptake of iron from the complex.
The use o$ an uncomplexed hydroxypyrone or a salt thereof in admixture with its iron complex may also have another advantage in addition to the prevention of dissociation of the iron complex under acidic conditions. Thus, in certain pathological conditions there may be an excess of iron deposited at certain sites even though the patient exhibits an overall anaemia. In these patients the use of such a mixture has the advantage that the iron complex will remedy the overall anaemia whilst the free hydroxypyrone will act to remove iron from pathological to physiological sites.
However, although it is preferable for the hydroxypyrone present in an iron donor to be rapidly metabolized in order that iron may be efficiently transferred to the binding proteins and eventually to the iron requiring mechanisms within the body, it is preferable for a hydroxypyrone being used as an iron remover not to be rapidly metabolized so that it remains in the system, taking up iron, for an extended period. Thus, for example, maltol is rapidly metabo-lized and is therefore particularly suited for use as an iron :

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-- 15 --complex, but for this same reason it is not appropriate for use ;n the free form. It is also the case that different compounds may function more efficiently either in the free form as an iron remover or in complex form as an iron donor for quite other 05 reasons. Alternatively, the different 3-hydroxy~ pyrone may be replaced by a quite differen-t form o-f iron chelating agent, examples of such other agents including the substituted

3-hydroxypyrid-2-ones and -4-ones (and salts of these pyridones containing d physiologically acceptable cation) ~lescribed in 10 UK Patent 2118176 (Application 8308056, published as 2118176A).
The present invention thus includes pharmaceutical compositions which contain the iron complex together with an iron chelating agent, particularly uncomplexed 3-hydroxy-4-pyrone or an uncomplexed 3-hydroxy-4-pyrone in which one or more of the hydrogen 15 atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, or a salt thereof containing a physiologically acceptable cation, the uncomplexed hydroxypyrone being the same or a different hydroxypyrone from that present in the complex.
When a free hydroxy-4-pyrone, hydroxypyrid-2-one, hydroxypyrid-

4-one or salt thereof, or other iron chelating agent is present in admixture with the iron complex of a hydroxy-4-pyrone for the purpose of acting as an iron remover, then the amount of this agent used may be different than when a free hydroxypyrone necessarily 25 corresponding to that present in the iron complex is present primarily to prevent dissociation. Thus the daily dosage of the iron complex may be as above and the daily dosage of the free iron chelating agent, particularly when this is a hydroxypyrid-2-or -4-one may be that quoted in UK Patent 2118176, i.e. about 0.1 g 30 to 5 9 for human use, particularly 0.5 g to 2 g, from which it will be seen that the proportion of iron complex and free iron chelating agent used in such a context may extend across a wide range but preferred amounts of the free iron chelating agent tend to be higher than when this is necessarily a hydroxypyrone.

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- l6 In addition to the pharmzceutical uses of the iron complexes discussed above they are also of potential interest as a source of iron in various other contexts including cell and bacterial growth, plant growth, and the control of iron transport across membranes.
05 This invention is illustrated by the following Examples:-EXAMPLES
(The names Nujol, Sephadex and Triton used in these Examples are Trade Marks.) _ ample l The preparation of iron maltol A chloroform solution of maltol is mixed with a lM solution of ferric chloride in ethanol to provide a 3:l molar ratio of maltol:iron in the mixture. After 5 minutes at 20C, a lO molar excess of solid sodium carbonate is added and the mixture is stirred for lO minutes The mixture is then filtered and the solvent evaporated to give the neutral complex containing maltol and the ferric cation in 3:1 proportion. Recrystallisation of the 3:1 complex from ethanol gives wine red needle crystals in an essentially quantitative yield, m.p. 275, V (nujol) ]600cm The use of an excess of maltol above the 3:l molar ratio leads to an essentially quantitative yield of a solid mixture of the excess- maltol and the 3:1 iron maltol complex on rotary evapora-tion, this mixture not being deliquescent.
The partition coefficient K t (concentration in n-octanol/
concentration in aqueous phase) between n-octanol and Tris hydro-chloride (20 mM, pH 7.4) of maltol and of its 3:l iron complex is measured at lO 4M by spectrophotometry. Acid washed glassware is used throughout and, following mixing for I minute, the aqueous/
n-octanol mixture is centrifuged at lO00 g for 30 seconds The two resulting phases are separated for a concentration determina-tion by spectrophotometry on each. For maltol, the range 220-3~0 nm is used for the concentration determination whilst for the complex the range 340-640 nm is used. Typically, a value of 0.66 is obtained for maltol and of 0.50 for its iron complex, whilst .,~ 2 ~ , ~, `-.

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- 16a -comparative experiments on iron(III) EDTA and iron(III) ascorbate give much smaller values of 0.00] and 0.0015, respec-tively.
The ability oE the iron complex of maltol to bind to haemo-05 globin is investigated by studying the elution profile of a 59Felabel when a mixture of haemoglobin and the 59Fe-labelled complex (at 1 mM concentration) in NaCl (]30 ~M) buffered to pH 7.4 by Tris hydrochloride is applied to a PD-]O column (Sephadex G-10 gel permeation column - Pharmacia), Typically, no evidence is found for binding of the complex to haemoglobin which is an advantageous finding since such binding reduces availability of the iron.
The ability of the iron complex of maltol to bind to bovine serum albumen (BSA) is investigated through a similar procedure in which the complex is applied to a column with BSA rather than haemoglobin. The iron complex also shows little ability to bind to BSA.

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Ex~ 2 In vitro tests on permeation of iron complexes into human erythrocytes The accumulation of iron by human erythrocytes which are 05 associated with the iron complex of maltol described in Example 1, and various other iron compounds by way of comparison, was studied by incubating the erythrocytes for 1 hour at 37C in a medium consisting of the 59Fe labelled iron compound in aqueous sodium chloride (130 mM) buffered to a pH of 7.4 by Tris hydrochloride.
Following this period of incubation an aliquot of the erythrocyte/
medium mixture was placed above a layer of silicone oil (P = 1.06) and the erythrocytes separated by centrifugation through the oil.
The Fe levels associated with the erythrocytes and the incubation medium were then counted and presented as a distribution ratio (concentration in erythrocytes/ concentration in medium)~ The ratios obtained for the various iron compounds after incubation for 1 hour are shown in Table 1 where it will be seen that the uptake of iron is clearly much greater with the iron maltol complex than with the other compounds. Values of less than 0.1 are probably associated with binding to the external surface and do not represent transmembrane movement of iron. Moreover, although a period of 1 hour was employed in order to facilitate monitoring of the more slowly permeating iron compounds, the uptake of the iron maltol complex reached equilibrium at the level shown after about 15 minutes.
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Table 1 ... _ . _ Concentration Distribution Compound (mM) ratio ~ .,... _ .....
Fe (maltol)3 3 1.60 Fe gluconate 1 0.08 Fe ascorbate 1 0.12 Fe citrate 1 0.05 FeIII EDTA 1 0.05 When the above described procedure was applied using ratios of maltol to iron of less than 3:1 larger apparent distribution ratios were observed than 1.60. However, this ls explained by the non-specific binding of the positively charged 2:1 and 1:1 maltol:
05 iron complexes to the surface of the erythrocytes which possesses a net negative charge, being rich in both phosphate and sulphate moieties. Experiments to determine the percentage o~ Fe associated with erthrocyte ghosts after lysis confirm this hypothesis. In one experiment, lysis was initiated by a small volu~e of 10% v/v Triton X100 and in a second experiment by a lO
fold excess o~ water. In each case the resulting ghosts were centrifuged through silicone oil (p = 1.02) and, as will be seen from Table 2, very little of the 3:1 maltol:iron complex was found to be bound to the membranes, in contrast with the situation with the 2:1 and 1:1 complexes. Such binding is of course undesirable as the complex is likely to remain tightly bound to the membrane by electrostatic interactions and not be transmitted across it.

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Table 2 _ _ ____ _ _.___ , Iron associatied with Ratio of with ghosts (%) maltol:iron ._ Triton lysis Hypotonic lysis 0: 1 100 1:1 55 63 2:1 22 39 3:1 <1 <5 Example 3 In vitro tests on per~eation of rat ~ejunal sac by iron complexes The iron uptake into the serosal space of the rat jejunal sac was compared for the iron complex of maltol described in Example 1 05 and various other iron compounds by way of comparison. Rats (male Sprague Dawley, 60 g) were killed and the jejunum removed, everted and cut into three segments (4 cm length). The segments were tied at both ends, filled with Krebs Ringer buffer (0.2 ml) and incubated in Krebs Ringer buffer containing the appropriate 59Fe compound at 37 C for periods up to 90 minutes. The contents of the sac were counted for 59Fe and measured spectrophotometrically.
The results obtained for the iron ~altol complex and for 6 other iron compounds which are each contained in preparations marketed for the treatment of iron deficiency anaemia are shown in Table 3, the iron uptake for each at 15 and 60 minutes after the initiation of the experiment being shown relative to that for ferric chloride as 1. It will be seen that the iron maltol complex provides a level of iron up~ake which is significantly higher than the levels observed for any of the 6 compounds in curren~ use for the treatment of iron deficiency anaemia. The uptake of the iron maltol complex was linear for a period of 90 minutesO Moreover, the uptake increased linear1y as the concentration of th~ complex~

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was increased over a range from 0.5 to 10 mM, so it does not show saturation kinetics and the process is thus non-facilitated and thereEore should occur in all natural me~branes.
Table 3 _____ . . . ~
Relative iron uptake Compound 15 minutes 60 minutes .............. ... ... ... .... ___ FeC13 1 Fe (maltol)3 40 So8 Pe sulphate 2.4 1.4 Fe fumarate 4.0 1.8 Fe gluconate 1.6 0.8 FeII succinate 2.0 1.0 Fe ascorbate 0.4 0.8 Fe citrate _ _ 1.8 05 The procedure described above was used to compare the uptake of iron from buffer containing differing molar proportions of maltol:iron. The results obtained are presented in Table 4 which shows the amount of irDn transferred via the maltol complex into the serosal contents of the sac, the basal uptake of iron measured in a control experiment being subtracted in each case. It will be seen that the amount of iron transferred in the case of a 3:1 molar proportion of maltol:iron(III) is much higher than in the other two cases and, moreover the low, but significant leYel of iron uptake observed in the case of a 2:1 ratio is attributed to the proportion of the 3:1 complex (containing 13% of ~he total iron) present under these conditions.

Table 4 Maltol/iron Iron uptake (molar ratio) (n mole) 1:1 1.6 2:1 4.0 3:1 30.0 Example 4 In vivo test of action of iron co~ounds in the rat The action of the iron complex of maltol described in Example 1 was compared with that of iron(II) sulphate, iron(III) EDTA (1:1 05 molar ratio) and iron(II) gluconate.
Groups of rats (300-350 g) wer~ anaesthetised with nembutal (0.25 ml) and then with ether. A mid-line incision was made and the 59Fe labelled sample (100 ~g Fe, 10 ~Ci) was passed into the lumen of the duodenum via a small incision. The l abdominal well was then closed with a suture. The animals were sacrificed 1, 2, 4 and 6 hours after the administration of the compound and ehe various organs were monitored for their 59Fe content. The data is presented as histograms in Figures 1 to 4 which relate to iron maltol, iron sulphate, iron EDTA and iron gluconate, respectively, and show the levels of 59Fe in cpm after various time intervals for the different organs, the data in each case representing a mean of the results for three indlvidual animals. In the case of the data for blood and stenlum (bone marrow) the counts given are cpm/ml and cpm/g respectively, whilst in all other cases they are the total cpm counts. The various histograms have been normalised and consequently are directly comparable.
A comparison between Figures 1 and 2 shows that the i neutral 3:1 maltol:iron(III) complex is markedly superior to iron(II~ sulpha~e for the introduction of iron via the rat intestine. The gut washings (~hich contaln non-absorbed iron) show a much lower level of counts for the maltol complex, and the :

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counts associated with the gut wall, liver, blood, bone marrow and spleen are correspondingly grea~er. It is clear from Pigure 1 that Fe associated with maltol enters the intestine wall very rapidly and from there it is eficiently removed by the blood 05 supply. Iron is deposited in the bone marrow continuously throughout the 6 hour period at an apparently constant rate.
The ~altol c~mplex is also more efficient than iron(III) EDTA as sh~wn by Figure 3. With the later complex, the gut washings remain high for 4 hours and may be presumed to decrease only due to the effect of natural b~el movements translocating material fr~m the portion under investigation to lower portions of the intestine. The levels in the intestine wall and blood are extremely low. Alt-hough iron is transferred to both bone marro~
and spleen, this is at reduced rates as compared to those cbtained with the maltol c~mplex. As shown by Figure 4, iron(II) gluconate proved more effective than the sulphate or the EDTA complex, although deposition in the gut wall was less than that cbserved with the ~4~tol comple~. The decrease ~S reflected in the lower levels of-59Fe in ~oth ~one marrow and the spleen, the difference 6eing particularly marked after 6 hours. In view of the much higher levels of 59Fe trapped in the intestine wall in the case of the maltol complex, it may be predicted that this compound facili-tates a more prolonged supply of iron than iron(II) gluconate.
This test illustrates the superiority of the neutral 3:1 mal~ol:iron(III) complex as campared with three commonly used "soluble iron" preparations for the movement of iron across the rat jejunal wall into the ~lood circulation, the iron maltol being very rapidly removed from the lumen of the intestine.
Example 5 In vivo test of action of iron complexes in the cat The action of the iron co~plex of maltol described in Example I
~as compared with that of iron~III) EDTA (l:l molar ratio) which is one of the iron compounds currently marketed for the ~reatment of iron deficiency anaemia. Cats were anaesthetised ~ith chlora-lase (60 mglkg) and pentc~arbitone sodium (60 mg/kg) (i.p.),havîng been kept free of food for 18 hours. In each animal the .. , ~

;
-trachea was cannulated to maintain a clear airway and to allow positive pressure artificial respiration if necessary. The left femoral vien was cannulated for the intravenous administration of drugs and physiological saline solution. Arterial blood pressure 05 was monitored by a Washington pressure transducer throu~h a cannula inserted lnto the femoral artery of the right hind leg. Arterial blood samples were taken at appropriate intervals from a short cannula inserted into an external carotid artery. Body tempera-ture was monitored with a rectal thermome-~er. Each animal was given heparin (1000 iu/kg) as anticoagulant and additional small amounts of pentabarbitone sodium if needed to maintain a satis-factory level of anaesthesia.
In those animals where the iron compounds were to be admini-stered into the duodenum, a mid-line incision was made in the abdomen to reveal the intestines. A cannula was then inserted through a small cut such that its tip rested approximately 5 cm below the opening of the bile duct. The cannula was then sutured in place and the abdominal wall closed with stitches.
l`he iron maltol complex (100 ~g Fe) alone (3.1 molar ratio of maltol:iron) and together with a large excess of maltol (40:1 molar ratio of maltol:iron) was injected intravenously in separate experiments and 0.25 ml samples of blood were taken at intervals.
The apparent volume of distribution of the compound was calculated by extrapolation of the log-linear blood concentration curve to zero. (The volume corresponds to a value between that of the total extracellular space of the animal and the blood volume.) Elimination of 59Fe from the blood followed first order kinetics with a rate constant of -0.022/minute in the presence and absence of excess maltol, as illustrated in Figure 5 which shows the 59Fe level in the blood in cpm/0.25 ml plotted against time in the case of one typical experiment of each type in an individual cat.
The distribution of 59Fe in the tissues of the animal after the same intravenous experiment to which Figure 5 relates (the ; lower end of the ordinate in this Figure represents the background level) wa~ investigated and the typical results are shown in Table 5. The amount of 59Fe administered in this experiment .., ~2f~
- 24 ~
was 4JuCi or 2.2 x 106 cpm. It will be seen that approximately 10 of the dose was located in the combined tissue of the heart, liver and spleen. AS less than 0.2~ of the dose was located in the urine, the bulk (approximately 90%) of the 59Fe ~as almost 05 certainly directed to the bone marrow and extremely hlgh lAvels were found to be located in the sternum.
As indicated previously, the maltol complex is able to donate iron rapidly to transferrin and it is hypothesised that such an exchange occurs as soon as the complex is delivered to the plasma;
and that the initial plateau (represented in Figure 5 by a dotted line) represents saturation of the plasma transferrin pool with 59Fe.
When there is net donation of 9iron from the plasma into the organs of the animal, the blood levels of radioactiv~ty begin to fall, the major rou~e of transfer of iron bound to transferrin being to ~he bone marrow, liver and spleen. Binding of 5 Fe tn transferrin prevents its excretion in the urine.
Table 5 .
(Iron maltol, i.v) :

Sa=ple Net Fe Net TissueTotal tissue weightcontent content weight (g) (g)(cpm1g)~cpm) Heart 14.4 0.91490 7,056 Liver 105 1.3510 53,550 Spleen 8.4 0.86149890125,076 Kidney 12.2 1.05546 6,661 Skeletal muscle _ 1.85 0 0 Sternum _ 1.239200 ~bone marro~) Urine _ 152 <3,000 Identical experiments carried out with 59Fe labelled iron(III) EDTA gave a entirely different picture as will be seen for the results of a typical experiment illustrated ~n Figure 6 .e 1 ~ `
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(in which the lower end of the ordinate represents the background level) and Table 6 (the amount of 59Fe administered in this experi-ment was 2flci but the Pigures given in the table have been adjusted to correspond to a dosage of 2.2 x 106 cpm in order to facllita~e 05 compar~son with Table 5). In this experiment the radloactivity ln the blood showed no initial plateau. Instead, loss of radioactivity followed at least a two-component process such that a large amoun~
found its way to the urine rather than to the tissues. The rate constant of ~he elimination from the blood of the linear phase of the regression was 0.023/minute. The concentration of radioactivity in the kidney and urine, and not in the bone marrow or spleen, would indlca~e that iron in this form does not sppear to be able to attach to transferrin in the plasma and protect ttself from urinary excretion. The combined tissue of heart, liver and spleen contained only 1% of the original dose at the end of the experiment, whereas ehe urine contained over 50%. This is in accord with ~he fact that EDTA does not exchange iron with transferrin rapidly.
Table 6 (Iron EDTA, i.v.) S~mpleNet Fe~o~l 59~e TissueTotal tissue weightcontentcontent weight (g) (g)(cpm/g) (~pm) Heart 15.5 1.01 209 3, 248 Liver 75 1. 21 261 19,600 Sternum _ 0. 281,164 (bone marrow) Spleen 11. 2 0 .89 162 1,814 Kidney 19.2 1.47 19134 21,770 Skeletal muscle _ 2.59 95 Urine 19 ml 2 ml62,1561,180,900 The iron maltol complex (100~ug Fe) was also administered to the duodenum of the cat in the presence of a 40 fold e~cess of ,~

maltol followed by 5 ml of 150 ml Tris hydrochloride buffer (pH 7.4).
In this case the 59Fe content of the blood, as shown in F$gure 7, reaches a maximum level 2 hours after the initial administration (the readings start at about 300 cpmlO.5 ml which represent6 the 05 background read~ng). The distrlbution of 59Fe in the ti6sues of the animal after ~he same duodenal experiment to which Flgure 7 relates were investigated and the typlcal results are shown in Table 7. The amount of 59Fe administered ln this experiment was 10~UCi or 5.327 x 106 cpm into a 2.9 kg cat. It will be seen that the distribution of the 59Fe after 4 hours was similar to that after in~ravenous infusion, with low levels in the kidney and urine and high levels in both the spleen and bone ~arrow.
T_ le 7 SIron maltol, per duodenum) _ _ I Net SampleNet 59Fetotal Fe ¦
~sue Total tissue ~ ht content content weight (g)(g)(cpm/g~ (cpm) Heart 14 0.633 50 1,106 ~iver 81 1.45 400 32,400 Spleen 12.7 1.19 3,783~8,047 Kidney 14.4 0.835 79 1,138 Sternum 10 1.26 790 7,905 (bone marrow) Bile ~5 ml 1 ml 2,200~11,000 Urine ~10 =l 1 ml 22 ~220 When 9Fe labelled iron(III) EDTA was admin1stered duodenally in the same manner, the plasma levels of radioactivity hardly exceeded the background level and are therefore not illustra~ed in a Figure.
The distribution of 59Fe in the tissues of the animal after the same duodenal experiment were investigated and the typical resul~s are shown in Table 8. The amount of 59Fe administered in this experiment was 10JuCi or 2.65 x 106 cpm into a 2.9 kg ca~. Ie - ` " ~ `~ '' ' ' :: ~

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will be seen that, although some 59Fe entered the tissues, rath2r low levels were detected in the spleen and bone marrow (sternum) whereas a large proportion of the dose was located in the urine.
Table 8 -05 (Iron EDTA, per duodenum) ~ _ Net SampleNe~ 59Fetotal 59Fe TissueTotal tissue weightcontent content welght (g) (g)(cpm/g) (cpm) __ Heart 15.3 1.18 188 2,~78 Liver 59.3 0.78 499 29,574 Kidney 11.3 0.901,762 19,913 Spleen 4.4 0.42 200 880 Sternum _ 0.78 917 _ (bone marrow) Skeletal ~uscle _ 1 48 117 Urine 15 ml 5 ml36,306 544,5~6 _ Example 6:
Polymer formulation of iron maltol ; A solution of ferric chloride (concentration between 1 and 5% w/v), together with maltol in a weight ratio of 8 parts by ~ lO weight of maltol to 1 part by weight of ferric chloride, is prepared- in a 4.5:4.5:1 v/v/v mixture of chloroform:methanol:water. Sodium carbonate is added ln a 10 molar excess over the iron content in order to remove hydrochloric acid and the precipitated NaCl and Na2C03 are filtered off. The preparation i6 contacted with a cross-linked polyethylene glycol hydrogel material to effect take up of the solution by the polymer and provide a polymer formulation of iron maltol in the presence of excess maltol.
Example 7 Capsule formula~ion of iron maltol A preparation of iron(III) maltol in admixture with maltol (containing 1 part by ~elght of iron to 10 parts by welght of ' : , .
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mal~ol) is obtained by the addition of a lM ethanolic solutlon of ferric chloride to a methylene chloride solution of the appropriate amount of maltol, followed after 5 mlnutes at 20 C by treatment with a 10 molar excess of solid solution carbonate, stirring 05 for 10 minutes, filtration and evaporation of the solven~.
The resulting solid iron(III) maltol preparatlon is divided into 50 mg quantities and added to standard gelatine capsules (16 x 5 mm), each capsule containing 5 mg of iron. The capsules are then coated with a cellulose acetate phthalate/diethyl-phthalate layer (6 mg coat per cm of capsule surface) in a smallscale procedure analogous to the procedure described by Jones, ibid.
A proportion of the capsules are treated to add a second similar coating.
Such capsules are resistant to dissociation in the stomach but will undergo dissociation in the intestine. Thus, when treated at 37C with dilute aqueous hydrochloric acid (pH 2.0) the singly coated capsules are typically stable for 30 minutes but in Krebs Ringer bicarbonate solution (pH 7.4) at 37C they dissociate to release the iron complex within 1 minute. The doubly coated capsules are typically stable at pH 2.0 for 20 hours, again dissociating within 1 minute at pH 7.4.
Example 8 LiDosome formulation of iron maltol (A) A solution of egg yolk phosphatidyl chlorine(1) (40 mg) and cholesterol (40 mg) in chloroform (1 ml) is rotary evaporated in a 50 ml round bottomed flash to form a thin lipid film. An aqueous solution of the 3:1 neu~ral iron(III) maltol complex (6 ml, 1 mg/ml) is added to the flask and the mixture is vibrated for 15 minutes.
Centrifngation (3,000 rev/~inute for 10 minutes) yields multilammelar liposomes contalning iron(III) maltol.
(1) In a modification of this procedure the phospholipid ~ay be varied among egg yolk phosphatidyl chlorine, dimyristoyl phospha-tidylcholine and dipalmitoyl phosphatidylcholine together with a preparation of cholesterol varying from 0 to 1 moles of cholesterol per mole of phospholipid.

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(B) A chloroform solution (2 ml) of the 3:1 neutral iron(III) maltol complex (5 mg/ml) is added to egg yolk phosphatidyl-choline ~lO0 mg) and cholesterol (50 mg). The solution is rotary evaporated to yield a deep red skin on the surface of a round 05 bottomed flask. Addition of 6 ml of a bufered solùtion o sodium chloride (100 mM, Tris.HCl: 20 mM, pH 7.4) ollowed by shaking for 15 minutes leads to a finely dispersed lipid-iron(III) maltol preparation. Centrifugation at 3000 revs/minute for 10 mlnutes yields a liposome preparation which can be readily freeze dried.
The entrapment of irontIII) maltol using this method is particularly efficient.
Liposomes produced by either method are resistant to dissocia-tion in the stomach but will undergo dissociation in the intestine.

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Claims (41)

- 30 -

1. A pharmaceutical composition comprising a physiologically effective amount of the neutral 3:1 hydroxypyrone:iron(III) complex of 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, together with a physiologically acceptable diluent or carrier but excluding any liquid which is not sterile and pyrogen free.

2. A pharmaceutical composition comprising a physiologically effective amount of the neutral 3:1 hydroxypyrone:iron(III) complex of 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, together with a physiologically acceptable solid carrier.

3. A pharmaceutical composition according to Claim 2, which is adapted for oral administration.

4. A pharmaceutical composition according to Claim 2 or 3, which is formed.

5. A pharmaceutical composition comprising a physiologically effective amount of the neutral 3:1 hydroxypyrone:iron(III) complex of 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, together with a physiologically acceptable diluent or carrier which includes a glycol or glycol ether.

6. A pharmaceutical composition according to Claim 5, which includes a polyethylene glycol.

7. A pharmaceutical composition comprising a physiologically effective amount of the neutral 3:1 hydroxypyrone:iron(III) complex of 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, together with a physiologically acceptable diluent, said composition being of a sterile injectable form.

8. A pharmaceutical composition comprising a physiologically effective amount of the neutral 3:1 hydroxypyrone:iron(III) complex of 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, together with a physiologically acceptable diluent or carrier, said composition being of a delayed release form.

9. A pharmaceutical composition according to Claim 8, which is adapted for release of the iron complex in the intestine rather than in the stomach.

10. A pharmaceutical composition comprising a physiologically effective amount of the neutral 3:1 hydroxypyrone:iron(III) complex of 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of l to 6 carbon atoms, together with a physiologically acceptable diluent or carrier, said composition being of a form resistant to dissociation under aqueous acidic conditions.

11. A pharmaceutical composition according to Claim 10, in which the iron complex is encapsulated by a material resistant to dissociation under aqueous acidic conditions.

12. A pharmaceutical composition according to Claim 11, in which the iron complex is encapsulated by a solid material which is resistant to dissociation under aqueous acidic conditions but which is adapted for dissociation under aqueous non-acidic conditions.

13. A pharmaceutical composition according to Claim 1, 2 or 8, in which the or each aliphatic hydrocarbon group is of 1 to 4 carbon atoms.

14. A pharmaceutical composition according to Claim 1, 2 or 8, in which the or each aliphatic hydrocarbon group is a cycloalkyl or alkyl group.

15. A pharmaceutical composition according to Claim 1, 2 or 8, in which the or each aliphatic hydrocarbon group is an acyclic group.

16. A pharmaceutical composition according to Claim 1, 2 or 8, in which the complex is of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by the same or different substituents selected from the group consisting of methyl, ethyl, n-propyl and isopropyl.

17. A pharmaceutical composition according to Claim 1, 2 or 8, in which the complex is of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by a methyl group.

18. A pharmaceutical composition according to Claim 1, 2 or 8, in which the complex is of a 3-hydroxy-4-pyrone having a single substituent at the 2- or 6-position which is selected from the group consisting of methyl, ethyl, n-propyl and isopropyl.

19. A pharmaceutical composition according to Claim 1, 2 or 8, in which the complex is the neutral 3:1 hydroxypyrone:iron(III) complex of 3-hydroxy-4-pyrone, 3-hydroxy-6-methyl-4-pyrone or 2-ethyl-3-hydroxy-4-pyrone.

A pharmaceutical composition according to Claim 1, 2 or 8, in which the complex is the neutral 3:1 hydroxypyrone:iron(III) complex of 3-hydroxy-2-methyl-4-pyrone.

21. A pharmaceutical composition according to Claim 1, 2 or 8, in which the complex is the neutral 3:1 hydroxypyrone:iron(III) complex of 2-ethyl-3-hydroxy-4-pyrone.

22. A pharmaceutical composition according to Claim 5, 7 or 10, in which the complex is the neutral 3:1 hydroxypyrone:iron(III) complex of 3-hydroxy-2-methyl-4-pyrone.

23. A pharmaceutical composition according to Claim 5, 7 or 10, in which the complex is the neutral 3:1 hydroxypyrone:iron(III) complex of 2-ethyl-3-hydroxy-4-pyrone.

24. A pharmaceutical composition according to Claim 1, in which the neutral 3:1 complex is substantially free from complexes containing other proportions of the hydroxypyrone and iron(III).

25. A pharmaceutical composition according to Claim 13, in which the iron complex is in substantially pure form.

26. A pharmaceutical composition according to claim 1, which contains an iron chelating agent as an additional active component thereof.

27. A pharmaceutical composition according to claim 26, in which the iron chelating agent is uncomplexed 3-hydroxy-4-pyrone or an uncomplexed 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms is replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, or a salt thereof containing a physiologically acceptable cation.

28. A pharmaceutical composition according to claim 27, in which the uncomplexed hydroxypyrone is the same as that present in the complex.

29. A pharmaceutical composition according to claim 28, which comprises the neutral 3:1 iron complex of 3-hydroxy-2-methyl-4-pyrone and uncomplexed 3-hydroxy-2-methyl-4-pyrone or a salt thereof.

30. A pharmaceutical composition according to claim 28, which comprises the neutral 3:1 iron complex of 2-ethyl-3-hydroxy-4-pyrone and uncomplexed 2-ethyl-3-hydroxy-4-pyrone or a salt thereof.

31. A pharmaceutical composition according to claim 28, 29 or 30, in which the molar proportion of uncomplexed hydroxypyrone:
iron(III) complex is from 1:1 to 100:1.

32. A pharmaceutical composition according to claim l, which contains folic acid as an additional active component thereof.

33. A pharmaceutical composition according to claim 1 in unit dosage form.

34. A pharmaceutical composition according to claim 33, in which the dosage is from 0.1 to 100 mg of iron as the complex

35. A process for preparing a medicament in ready-to-use form for use in effecting an increase in the amount of iron in the bloodstream of a patient to whom the medicament is administered, which process comprises incorporating in the medicament as an active ingredient an iron complex of 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms is replaced by an aliphatic hydro-carbon group of 1 to 6 carbon atoms.

36. A process according to claim 33, in which the iron complex is the neutral 3:1 hydroxypyrone:iron(III) complex.

37. A process according to claim 35 or 36, in which the com-plex is of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by the same or different substituents selected from the group consisting of methyl, ethyl, n-propyl and isopropyl.

38. A process according to claim 35 or 36, in which the com-plex is of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by a methyl group.

39. A process according to claim 35 or 36, in which the com-plex is of a 3-hydroxy-4-pyrone having a single substituent at the 2- or 6-position which is selected from the group consisting of methyl, ethyl, n-propyl and isopropyl.

40. A process according to claim 35 or 36, in which the com-plex is of 3-hydroxy-2-methyl-4-pyrone.

41. A process according to claim 35 or 36, in which the com-plex is of 2-ethyl-3-hydroxy-4-pyrone.