IE48231B1 - Pharmaceutical formulations containing prostaglandin compounds - Google Patents

Abstract

Stabilised pharmaceutical formulations of prostacyclin, 15- methyl-prostacyclin or 16,16- dimethylprostacyclin are prepared by addition of a buffer comprising an amino acid (preferably glycine) as the principal buffering agent.

Description

The present invention relates to pharmaceutical compositions containing prostacyclin (PGI2, PGX), 15-methylprostacyclin, 16, 16-dimethylprostacyclin, or their pharmaceutically acceptable salts.

Prostacyclin and its salts are important in human medicine and veterinary practice as they have a powerful antiaggregating action on blood platelets and also accelerate wound healing and prevent, or have a therapeutic effect on, stomach ulcers.

The anti-aggregatory effect on blood platelets is useful, for example, in preventing or mitigating the formation of thrombi or emboli during extracorporeal circulation of blood, e.g. in ranal dialysis and cardio-pulmonary by-pass.

However, a difficulty experienced with prostacyclin and its salts is that prostacyclin and its salts are unstable, especially in aqueous solution, and are quickly transformed . -.- -*»- · ' :'-ri-s:i-flto.6-oxo-PGP^a and its salts, which are almost pharmacologically inactive and have very few, if any, of the beneficial activities of prostacyclin and its salts.

Prostacyclin and its salts are known to be more stable in alkaline media than in acidic or neutral media. Although some improvement in stability has been obtained by using tris buffer in alkaline solution, the prostacyclin has still been rapidly decomposed. This has meant that the prostacyclin has had to be made up very shortly before use by, say, intravenous infusion, and the pharmocological activity of the solution has changed considerbly while it has been waiting to be used. This has made it difficult for the infusion to be controlled as carefully as desirable.

We have now surprisingly found that a marked improvement in stability can be obtained by having the prostacyclin, 15methylprostacyclin, 16, 16-dimethylprostacyclin, or a salt thereof, preferably the sodium salt, (hereinafter referred to as the active compound), in association with a pharmaceutically acceptable buffer based on an amino acid as the principal buffering acid in the buffer. The active compound and the buffer may be in association in the solid state and in solution in a solvent, usually water. When the active compound and buffer are in solution, the pH measured is that of the solution containing said active compound and buffer, and said formulation or buffer preferably has a pH of at least 9.

If the active compound and the buffer are in association in the solid state, by pH measured in any one of the following ways. If the solid is a frozen solution, then - 4 the pH measured is that of the solution resulting from thawing the frozen solution. For other solid states, the pH measured is that of the solution resulting from dissolving the associated active compound and buffer in Water for Injections having a pH value of 7. For the particular case of a freeze dried residue in the minimum volume of Water for Injections having a pH value of 7 required to produce a clear solution.

In the solid state, the freeze drying of such a solution results in improved stability of the active compound.

Freeze drying may be effected in the conventional manner in, for example, an ampoule or vial. The solution may also be frozen and stored at, say, -20°C for use as a frozen injection or for diluting on thawing.

Such a solution and all solutions hereinafter referred to are, for medicinal purposes, to be understood to be sterile solutions.

Prostacyclin and analogues thereof, in particular 15methylprostacyclin and 15, 16-dimethylprostacyclin and a salt of one of these may be prepared by methods described in our Patent Specification No. 46036 for the preparation of compounds of analogous structure. These include dehydrohalogenation of a compound of formula (1): - 5 X Ο. \ S. wherein X is bromo or iodo; Y is OH, NHR^ or OR, R being alkyl of 1 to 4 carbon atoms or a pharmaceutically acceptable cation such as sodium, R being alkyl of 1 to 4 carbon atoms 12 3 R , R and R are independently selected from hydrogen and alkyl of 1 to 4 carbon atoms particularly methyl, with a 1 2 3 base; for example, when R is hydrogen R and R are both methyl and vice-versa; and converting, if necessary, the 4 4 resulting compound in which Y is NHR or OR, R and R being alkyl of 1 to 4 carbon atoms, into the desired active compound.

The amino-acid for use in the buffer if preferably sulphurfree and the most preferred amino-acid is glycine, especially as it is readily available and, if prepared synthetically, does not need to be optically resolved; but other amino15 acids such as valine, alanine and arginine may also be used.

The total concentration of amino-acid (i.e. including its salts) in the pharmaceutical formulation is preferably as -βίαν as is consistent with obtaining a stable buffer, e.g. in the range of from 0.02M to 0.03M, preferably about O.O25M, as the presence of too much amino-acid tends to reduce the stability of the active compound by increasing the ionic strength of a solution of the associated active compound and buffer. The amino-acid must be sufficiently soluble to provide the necessary buffering capacity.

If sodium chloride is present in a solution of the buffer, as is preferred, the amount added should not be such that the solution is pharmaceutically unacceptable. The molar concentration of sodium chloride is preferably about the same as that of the amino-acid. Too much sodium chloride would raise the ionic strength of a solution of the associated active compound and buffer undesirably and adversely affect the stability of the active compound.

Other salts, e.g. potassium chloride, may also be present if they, or their amounts, are pharmaceutically acceptable.

The pH of the buffer is preferably 10.2 to 11.6, especially about 10.5, when measured by the appropriate method as hereinabove described.

As an example of preparing a buffer solution according to the invention containing prostacyclin, a solution of glycine in water and also containing some sodium chloride was prepared. To this solution was added sodium hydroxide as base to raise the pH to the desired level and then the - 7 prostacyclin was added.

Although sodium hydroxide was used as base in the above example, any base may be used that is strong enough to give a buffer solution of the desired pH. Naturally the base should be one that gives rise to a pharmaceutically acceptable solution, i.e. one that is not deleterious to the recipient. The amount of amino-acid, for example, glycine and base, for example, sodium hydroxide, used should be as little as is necessary to stabilize the active compound for the period of time required. Use of excess of either or both amino-acid or base results in retention of water in a freeze dried product which brings about deterioration of the active compound. However, the pH of the solution is an important factor in assessing pharmaceutical acceptability. If the buffer solution is to be introduced into a machine for example in renal dialysis, then the pH can be up to 12 or even more, but if the buffer solution is to be administered in a large volume into a vein, for example in cardio-pulmonary by-pass, then the pH on entering the vein should preferably be in a range of from 8.4 to 9, and for this the pH of the buffer solution can be lowered shortly before use.

Other buffering agents may be present in the buffer solution but their amount should not substantially reduce the stability of the active compound in the solution. For example, some carbonate may be present, derived from the prostacyclin, - 8 e.g. prostacyclin sodium may contain up to 5% by weight of sodium carbonate.

As the active compound is very active pharmacologically, the amount of it needed is very small; for example only a few minigrams are needed for a one hour infusion into an average person of 70 kg body weight. The amount of active compound present in a given buffer solution before freeze drying depends on the projected use for the freeze dried material on reconstitution. The reconstitution may be with buffer solution free of active compound so that the ratio of active compound to buffering constituents may be much greater than in the solution used for administration.

If a solution containing only buffering agents, active compound and sodium chloride is freeze dried, the physical strength and appearance of the freeze dried plug obtained are not particularly satisfactory. It is accordingly preferred to include an excipient in the buffer solution before freeze drying the solution. The preferred excipient is mannitol. Preferably the concentration of excipient is from 25 to 50 mg/ml of buffer solution. For mannitol if less than 25 mg/ml is used there is insufficient improvement in strength and appearance. If more than 50 mg/ml is used there is little or no further improvement and the stability of the active compound may be adversely affected. The excipient provides, in the freeze dried plug, a supporting matrix and improves the physical strength 48331 - 9 and appearance of the plug. Not all excipients may bfe used; for example those producing excessive foaming of the reconstituted material in the freeze drying vial, e.g. polyvinylpyrrolidone, should be avoided. Also, others affecting the pH of the buffer, e.g. glycine itself, should be avoided.

The buffer solution may also contain, if desirable, other therapeutic material besides the active compound. A freeze dried product may also contain such other therapeutic material or these may be added to the reconstituted buffer solution. Such other therapeutic material may partly or completely replace the excipient.

The solvent used in preparing the buffer solution is preferably Water for Injections (European Pharmacopeia) or other water suitable for use in infusions or injectsion.

When reconstituting the freeze dried material for use, it may be redissolved in Water for Injections generally having a pH value in the range of from 5.5 to 7, preferably 7, or in amino-acid buffer solution having a pH of at least 9, preferably about 10.5, or perhaps some of the buffer solution may be added to a solution in Water for Injections. Reconstitution of the freeze dried material may also take place by dissolving it in an infusion base, such as physiological saline suitable for infusion. It is also possible to use glucose for this purpose.

The freeze drying of the buffer solution may be carried out in any conventional manner, with the water content of the plug being lowered as far as convenient to improve further the stability of the active compound.

The amount of active compound required for therapeutic effect varies with the route of administration. In general, a suitable dose for a mammal will lie in the range of from 0.01 to 200 mg. per kilogram body weight, conveniently of from 0.01 to 10 mg/kg, preferably of from 0.1 to 1.0 mg/kg, and especially of from 0.2 to 0.5 mg/kg.

The amount of active compound present in an ampoule for administration by infusion will lie in the range of from 0.1 to 1.5 mg/kg, preferably of from 0.5 - 1.0 mg/kg.

When used in man, the active compound may be several times more potent than in other mammals, and accordingly it may be desirable to use doses which appear at the lower ends of the dose ranges given hereinabove.

For human and veterinary use, it may be convenient to provide a collection of at least two vessels, for example as a multicomponent pack; one of which is a vial or ampoule containing a freeze dried (lyophilised) plug of the buffered active compound as described hereinabove, another vessel of which is a vial or ampoule containing a further amount of the buffer in aqueous solution or freeze dried which does not contain the active compound. The freeze dried product may then be reconstituted with the aqueous buffer, - 11 or where the contents of the second vessel are freeze dried, with a suitable aqueous diluent from a third vessel. The reconstituted material may then be diluted further, if required, to provide the desired dosage immediately prior to administration. Thus a freeze dried preparation of, for example 0.5 mg active compound, at pH 11.5 may be diluted, with 50 or 500 ml of aqueous dextrose or saline solution having a pH such that the resultant solution has a pH of 10.0 to 10.5.

Accordingly the present invention provides the following: (a) A pharmaceutical formulation comprising an active compound selected from prostacyclin, 15-methylprostacyclin, 16, 16-dimethylprostacyclin or a salt of any one of these, in association with a pharmaceutically acceptable busser based on an amino acid as principal buffering agent, the formulation having a pH of at least 9; (b) A method of preparing a formulation according to (a), which comprises bringing the ingredients into solution in a suitable solvent; (c) A freeze dried material obtained by freeze drying a formulation according to (a); (d) A frozen injection obtained by freezing a formulation according to (a); - 12 (e) A pharmaceutical formulation suitable for injection or infusion obtained by dissolving a freeze dried material according to (c) in a suitable solvent, or thawing a frozen injection according to (d); (f) A formulation according to (a), for use in (i) inhibiting the aggregation of blood platelets (ii) effecting vasodilation, and/or (iii) the treatment or prophylaxis of thrombosis, high blood pressure or gastric lesslons.

The present invention is illustrated by the following examples: EXAMPLE 1 Sterile solutions containing prostacyclin (0.2 mg/ml) were prepared in the following buffers: glycine, orginine, valine, alanine, carbonate, and tris. The concentrations of the buffering components were: Amino Acid Buffer: O.O25M amino acid, O.O25M sodium chloride and sodium hydroxide q.s. pH 10.5.

Carbonate Buffer: 448 mg/1 sodium bicarbonate and 1614 mg/1 sodium carbonate.

Tris Buffer: 6054 mg/1 of tris base and 2.5 ml of 0.1N sodium hydroxide per litre. 48331 - 13 5 ml portions of each of these solutions were then freeze dried in vials by freezing at -40°C and under vacuum, carrying out first stage drying at 0°C and second stage drying at 20°C. Sealing of the vials was conducted in a nitrogen atmosphere. The freeze dried products were then subjected to an accelerated storage test at the temperature shown in Table 1. The products obtained after the times indicated in Table 1 were analysed for their prostacyclin content by high performance liquid chromatography (HPLC). The HPLC was carried out on freeze dried preparations reconstituted in 10ml of 0.025% tetramethylammonium hydroxide solution.

The column used was a 25cm x 4.2mm X.D. stainless steel one filled with laboratory prepared Partisil ODS packing material made as given below. The column was packed using the method of Webber and McKerrel, J. Chromatog, 122, 243, (1976), employing carbon tetrachloride as the slurry medium.

The column packing material was prepared as follows, 10 pm Partisil (Partisil is a Registered Trade Mark) (10 g) was dried at 80°C in vacuo for two and half hours in a 250ml round bottomed flask. Octadecyltrichlorosilane (10ml) and dry toluene (100 ml) were added and the solution was refluxed for three hours with paddle stirring using a reflux condenser fitted with a calcium chloride guard tube. The mixture was allowed to cool and then filtered through 8 2 3 1 a 0.5 pm millipore filter. The silica in the filter was washed with 250 ml methanol, slurrying the solid continuously, then with 250 ml hot acetone and dried at 8O°C in vacuo for about two hours. The product (11 g) was treated with trimethylchlorosilane (10 ml) as above, refluxing for 45 minutes to give the final product.

The mobile phase used was water (1200 ml) in which was dissolved 5 g boric acid and 7.6 g di-sodium tetraborate and then methanol (800 ml) was added. The column temperature used was ambient i.e. about 25 to 30°C, and the mobile phase flow rate was 3.6 ml/min. and the pressure used was 20 MPa. Detection of the products was carried out using a Pye Dnichem LC3 (Pye is a Registered Trade Mark) at 205 nanometres wavelength, 0.16 aufs (absorbance units full scale) for 0 to 100 |ig/ml solutions.

The amount of prostacyclin present was determined by peak height measurement and comparison with a reference sample of known concentration.

The results of prostacyclin present was determined by peak height measurement and comparison with a reference sample of known concentration.

The results obtained are set out in Tables 1 and 11, each of which refer to 0.2 mg/ml of prostacyclin. - 15 TABLE 1 Buffer HPLC assay (% prostacyclin remaining) 66 hours 6 days (144 hours) 70°C 60°C 50°C 37°C 26°C Glycine 0 0 3 90 96 Carbonate 0 2 3.5 45 62 Tris 0 0 trace trace 35 TABLE 11 Buffer HPLC assay (% prostacyclin remaining) 66 hours 50°C 37°C Arginine 45% 91% Valine 86% 93% Alanine 83% 97% It can be clearly seen from Tables 1 and 11 that at normal storage temperatures, i.e. about 37°C or below, the amino5 acid buffers are superior to the other two buffers tested. Although the carbonate buffer is inferior to the amino4 8 2 3 1 - 16 acid buffer, it is clear that some carbonate could be tolerated in the amino-acid buffer.

EXAMPLE 2 Freeze dried injection of prostacyclin (i mg) Prostacyclin 1.000 mg Mannitol 50.000 mg NaCl (O.O25M) 2.932 mg Glycine (O.O25M) 3.760 mg NaOH q.s. to pH 10.5 EXAMPLE 3 Sterile Diluent for Injection of Prostacyclin Glycine (O.O25M) 94.0 mg NaCl (0. ,O25M) 73.3 mg NaOH q.s. to pH 10.5 Water for Injections up to 50 ml Using the general procedure described in Example 1, the above ingredients were used in a solution for use as a diluent.

Claims (19)

1. A pharmaceutical formulation comprising an active compound selected from prostacyclin, 15-methylprostacyclin, 16, 16-dimethylprostacyclin and a salt of any one of these, 5 in association with a pharmaceutically acceptable buffer acid based on an amine/ as principal buffering agent, the formulation having a pH of at least 9.

2. A formulation as claimed in claim 1 wherein the active compound is in solution in a solvent. 10

3. A formulation as claimed in claim 2 wherein the solvent is water.

4. A formulation as claimed in claim 2 or claim 3 wherein the solution containing the active compound and the buffer is freeze dried or frozen. 15 5. A formulation as claimed in any one of the preceding claims wherein the amino acid is sulphur-free. 6. A formulation as claimed in claim 5 wherein the amino acid is glycine. 7. A formulation as claimed in claim 5 wherein the 20 amino acid is selected from arginine, valine and alanine. - 18 8. A formulation as claimed in any one of the preceding claims wherein the total concentration of the amino acid (including its salts) is in the range of from 0.02 to 0.03M. 9. A formulation as claimed in claim 8 wherein the total 5 concentration of the amino acid (including its salts) is about 0.025M. 10. A formulation as claimed in any one of the preceding claims wherein a pharmaceutically acceptable amount of sodium,chloride is present. 10 11. A formulation as claimed in any one of the preceding claims wherein the pH of the formulation is in the range of from 10.2 to 11.6. 12. A formulation as claimed in any one of the preceding claims containing a pharmaceutically acceptable excipient. 15 13. A formulation as claimed in claim 12 wherein the excipient is mannitol. 14. A formulation as claimed in any one of the preceding claims wherein the active compound is prostacyclin or a salt thereof. 20 15. A formulation as claimed in any one of the preceding claims wherein the salt is a sodium salt. 19 16. A formulation as claimed in claim 15 wherein the active compound is prostacyclin sodium salt. 17. A formulation as claimed in claim 1, in freezedried form, comprising, as active ingredient, prostacyclin

5. Sodium salt, in association with a pharmaceutically acceptable buffer based on glycine as the principal buffering agent, the formulation having a pH of 10.2 to 11.6. 18. A formulation as claimed in claim 17 containing glycine in a concentration of 0.02 to 0.03M.

6. 10 19. A formulation as claimed in claim 17 or 18 containing a pharmaceutically acceptable excipient comprising mannitol. 20. A formulation as claimed in any of claims 17 to 19 containing a pharmaceutically acceptable excipient

7. 15 comprising mannitol. 21. A formulation as claimed in any of claims 17 to 20 wherein the formulation is disposed in one vessel of a collection of two sealed vessels, the second vessel containing a pharmaceutically acceptable buffer based on

8. 20 glycine as the principal buffering agent and having a pH of 10.2 to 11.6. 4823 1 - 20 22. Λ method of preparing a pharmaceutical formulation which comprises bringing an active compound selected from prostacyclin, 15-methylprostacyclin, IS, 16-dimethylprostacyclin, or a salt of any one of these into association 5 with a pharmaceutically acceptable buffer based on an amino acid as principal buffering acid in the buffer, the resulting formulation having a pH of at least 9.

9. 23. A formulation as claimed in any of claims 1 to 16 wherein the buffer comprises an amino acid and a strong base 10

10. 24. A formulation as claimed in claim 23 wherein the strong base is sodium hydroxide.

11. 25. A formulation as claimed in any of claims 1, 5 to 16 and 23 and 24 wherein the formulation is disposed in a freeze-dried state in one vessel of a collection of at least 15 two sealed vessels, a second vessel thereof containing the pharmaceutically acceptable buffer as defined in the preceding claims.

12. 26. A formulation as claimed in claim 25 wherein the □econd vessel also contains sodium chloride. 20

13. 27. A formulation as claimed in claim 25 or claim 26 wherein the mixture in the second vessel is in aqueous solution. - 21

14. 28. A formulation as claimed in claim 25 or claim 26 wherein the mixture in the second vessel is freeze dried.

15. 29. A formulation as claimed in any one of claims . 1 to 21 to 28 for use in inhibiting the aggregation of blood 5 platelets.

16. 30. A formulation as claimed in any one of claims 1 to 21 or 23 to 28 for use in effecting vasodilation.

17. 31. A formulation as claimed in any one of claims 1 to 21 or 23 to 28 for use in the treatment or prophylaxis 10 of thrombosis, high blood pressure, or gastric lesions.

18. 32. A formulation according to claim 1, substantially hereinbefore described in any one of Examples 1 to 3.

19. 33. A method according to claim 22, substantially as hereinbefore described in any one of Examples 1 to 3.