THYROXINE/CYCLODEXTRIN COMPLEXES AND PHARMACEUTICAL COMPOSITIONS CONTAINING THE SAME

Abstract: Thyroxine containing pharmaceutical compositions with improved aqueous solubility, stability and enhanced membrane permeation have been prepared by formulating thyroxine with cyclodextrins. These thyroxine/cyclodextrin complexes can further be transformed into different dosage forms (oral tablets, injectables, transdermal patches, hydrogels, ointments, suppositories, etc.) by employing known, common pharmaceutical additives.

Description: Thyroxine/Cyclodextrin Complexes and Pharmaceutical Compositions containing the same Thyroxine containing pharmaceutical compositions with improved aqueous solubility, stability and enhanced membrane permeation have been prepared by formulating thyroxine with cyclodextrins. These thyroxine/cyclodextrin complexes can further be transformed into different dosage forms {oral tablets, injectables, transdermal patches, hydrogels, ointments, suppositories etc.) by employing known, common pharmaceutical additives . The present invention relates to complexes of thyroxine and cyclodextrin and pharmaceutical compositions thereof suitable for oral, and parenteral or transdermal administration. In the present invention thyroxine stands for L-thyroxine or D-thyr¬ oxine or a pharmaceutical acceptable salt thereof or any race- mate thereof . Deficiency of thyroid activity, whether occurring spontaneously or resulting from surgical removal of thyroid gland, thyroidi- tis, or decreased function secondary to pituitary degeneration results in clinical hypothyroidism. Whatever the cause, the symptom is treated by replacement therapy using thyreoglobulin or salts of thyroxine, like Levothyroxine-sodium. Levo thyroxine (L- thyroxine) {0- (4-hydroxy-3 , 5-diiodόphenyl) - 3 , 5-diiodotyrosine} is an iodinated aminoacid of the thyroid gland that exerts a stimulating effect on metabolism (Kendall, J.Am.Med.Assoc. 64. 2042. 1915.) . Levothyroxine sodium as drug has been used mainly in tablet form with a unit dose of around 0.1 mg per tablet. SUBSTITUTΕ SHEET (RULE 26) Dextro thyroxine (D- throxine) is the D-configuration of the natural occuring thyroid gland hormone and exhibits chole¬ sterol and lipid lowering effects. Cyclodextrins (CDs) are prepared from starches using CD-glu- cosyl transferase enzyme. There are three different kinds of CDs, i.e. the - , &- and ^-CD, which consists of 6, 7 or 8 glucopyranose units connected with -1.4 glucosidic bonds. The three cyclodextrins differ in molecular weight, water-solu¬ bility and in cavity-diameter. Accordingly they are able to form inclusion complexes with most of compounds, but the inclusion complexes of the same compound are formed with different kinds of CD having very different properties. There is a possibility to carry out further modifications in the CD molecule with suitable substitutions. For example in case of heptakis-2, 6-di-O-methyl-β-CD (DIMEB) two hydroxyl groups of every glucose unit are methylated, while in case of randomly methylated β-CD (RAMEB) the hydroxy groups are substituted randomly by methoxy groups, however the average degree of methylation is around 1,8. The hydroxyalkylation of cyclodex¬ trins also results in improved aqueous solubility as known for hydroxypropylated and hydroxyethylated cyclodextrine derivatives (Szejtli, J. Cyclodextrin Technology, Kluwer Academic Publ.1988. page 51.) . The solubility of these chemically modified cyclodextrins reaches the value of about 400-500 mg/ml at room temperature and their complex-forming capacity also differs from the unsubstituted CDs. The interaction of thyroxine with cyclodextrins has not yet been reported. Thyroxine/cyclodextrin inclusion complexes as ingre¬ dients of any pharmaceutical formulations have never been previously described in any paper or patent. The U.S. Patent No.4121975 (Ull an, E. ; Lavine, F. and Joel, E.) deals with the analytical determination of serum thyroxine SUBSTITUTE SHEET (flULE 26) levels in patients by competitive protein-binding or immuno¬ assay, employing also }f- cyclodextrin for the selective removal of interfering components (mainly blood lipids) present in the blood samples. There is a lot of literature - both publications and patents - which describes the enhancement of poorly soluble drugs with cy¬ clodextrins and with the concomitant consequences, like improved bioavailability, chemical and/or physical stability of the cy- clodextrin complexed drug (Szejtli, J. : Cyclodextrin Technology, Kluwer Academic Publ., Dordrecht, Holland, 1988, p. 186-197) . Summarizing the available data it can be stated that in most cases the β-CD is the best complexing agent for hydrophobic, poorly soluble drugs and among the β-cyclodextrins the alkylated (methylated) and the hydroxyalkylated (hydroxypropylated) β-cy¬ clodextrins are the most appropriate ones. Only in a few cases the Y~cyclodextrin showed to be as good as a β-cyclodextrin derivative and in no case it has been published that the chemically non-modified, so-called parent ^-cyclodextrin - at identical cyclodextrin concentration - results in a more than 2.5-fold solubility enhancement as compared with the best solubilizer known, the heptakis- (2, 6-di-0-methyl) -β-cyclodextrin (Pitha, J. Life Sci .29.367.1981) . This unexpected experimental finding is the core of the present invention. It is well-known, that ^-cyclodextrin exhibits the highest aqueous solubility among all parent-cyclodextrins. However, its solutions are physically not stable, because the aqueous solu¬ tions of highly purified Jf*-cyclodextrins tend to become turbid within days at room temperature, even at 1/5 of the saturation concentration. A further unexpected observation is that these f- cyclodextrin containing aqueous solutions and hydrogels remain clear without formation of any solid crystalline or amorphous precipitate. The unexpected excellent physical stability of aqueous thyr¬ oxine// * -cyclodextrin solutions in the physiologically acceptable pH-range is the other essential feature of our invention, be¬ cause only the simultaneous prevalence of these two properties makes it possible to prepare a thyroxine/^-cyclodextrin con¬ taining transdermal patch formulations. High concentrations of drug as well as physical stability of the solution and chemical stability of the dissolved drug are the preconditions for an appropriate transdermal thyroxine patch formulation. Interaction between L- thyroxine sodium and cyclodextrins in presence of water. One evidence of the interaction between L-thyroxine and cyclo¬ dextrins is that the cyclodextrins increase the aqueous solubi¬ lity of the thyroxine as shown in Table 1. Table 1 : Solubility of L-thyroxine sodium salt in the presence of CDs (mg/ml) cone, of ^-cyclo- 2 -hydroxy - randomly- heptakis-2,6-di- Maltosyl-β- CDs ( % ) dextrin propylated-β- methylated-β- O-methyl-β- cyclodextrin cyclodextrin cyclodextrin cyclodextrin 0 (no. CDs) 2.0 2.0 2.0 2.0 2. 0 1.0 5.48 1.44 3.70 3.16 2. 29 CΛ X m 3.0 12.10 3.10 6.15 5.50 2. .48 rπ 5.0 16.90 2.90 8.36 7.00 2. .32 ro 7.0 26.55 2.74 9.33 7.62 2 .94 c > 10.0 27.00 2.77 10.32 8.20 2 .73 12.0 35.10 3.05 13.30 12.13 2 .80 15.0 44.20 3.14 16.80 14.24 2 .68 As can be concluded from the above data, among the studied un¬ substituted cyclodextrins the ^-cyclodextrin was found to improve the aqueous solubility of L-thyroxine sodium most remarkably, thus to have the highest affinity towards the drug. It has unexpectedly been found that among the highly water- soluble β-cyclodextrin derivatives methylated-β-cyclodextrins (both randomly methylated and heptakis 2, 6-di-O-methyl- cyclodextrins) appear to be less potent solubilizers of thyroxine, than the chemically non-modified -cyclodextrin. It is further demonstrated that 2-hydroxypropylated β-cyclodextrin (HPBCD) and maltosyl-β-cyclodextrin have shown not to be really feasible solubilizing agents for thyroxine, since they did not significantly improve the aqueous solubility of thyroxine even at higher applied concentrations. It is also important that the parent a-cyclodextrin and β-cyclo¬ dextrin had practically no effect on the solubility of thyr¬ oxine. Thyroxine/Cyclodextrin Formulations Thyroxine can react with the cyclodextrins or their derivatives in aqueous medium. Having attained the required clarity of common aqueous solutions, water can be removed from the reaction mixture by known methods, i.e. by freeze-drying or spray drying. In certain cases, when necessary, only a small amount of a suitable, pharmaceutically acceptable organic solvent or deter¬ gent can be used as a third component in the formulations. According to an alternative method, the thyroxine and cyclodex¬ trins can be kneaded in the presence of small amounts of water. Pharmaceutical Dosage Forms The thyroxine/ cyclodextrin complexes can be used for the preparation of common pharmaceutical dosage forms like tablets, gels, ointments, cremes, injectables, suppositories, patches and plasters . For the preparation of tablets the complexes are either freeze- dried or spray-dried and mixed with suitable excipients to obtain fast or slow release tablets. Hydrogels containing the complexes of the present invention can be prepared by using water swellable polymers like polymers of acrylic acid, cellulose derivates, polyvinylpyrrolidone or gela¬ tine. Additionally, the aqueous solutions according to the invention can obtain stabilizers, antioxidants, or thickeners like pectins, alginates or silicium dioxides. Hydrogel preparations or aqueous solutions of the complexes may be filled in reservoir patches as described in the prior art. The following examples serve for illustration and do not limit the present invention. Example 1 : Prepara tion of thyroxine/ ^- cyclodextrin formula tion 20 ml of a 10 % aqueous >-CD solution was intensively stirred at room temperature and to this solution 500 mg of L-thyroxine-Na is added without any solvent. The reaction mixture was further stirred for 12 hours at room temperature with 600 r.p.m. The resulting slightly opalescent solution was then freeze dried yielding 2.28 g of white, nearly amorphous solid that has a thyroxine content of 20.12 % by weight. RECTIFIED SHEET (RULE 91) ISA/ EP Redissolution properties of the product according to Example 1: The reconstitution of this lyophilized powder results in a slightly opalescent solution, when 0.1 g of the product is dis¬ solved in 2 ml of distilled water (no solid particles are ob¬ served upon standing for two hours) . Example 2 : Preparation of thyroxine /randomly methyla ted-β- cyclodextrin for¬ mula tion 100 mg of L-thyroxine-Na is added to 10 ml of 10 % aqueous methylated-β-cyclodextrin solution (average degree of methylation is 1.8 methoxy per glucose unit) and the reaction mixture is stirred for 12 hours at room temperature. The slightly opalescent solution is filtered across a membrane of 0.42 and the clear filtrate is lyophilized. The resulting white amorphous powder is 1.07 g. The L-thyroxine content of the formulation is 9.25 % by weight. The redissolution properties of the product prepared according to Example 2. The formulation can be dissolved in water or in physiological buffered saline resulting in a clear, transparent solution. Example 3 : Prepara tion of L- complex by kneading 6.48 g (0.005 mole) of Ϋ- -cyclodextrin is wetted with 10 ml of deionized water and intensively grounded for 5 minutes. 0.799 g (0.001 mole) of L-thyroxine-Na is added to the j^-CD. The mixture is kneaded for 30 minutes at room temperature to obtain a white cream. The creamy material is dried over P 2 0 5 at room temperature to constant weight. The dry complex is a white or nearly white powder that has a thyroxine content of 10.6 % by weight. Example 4 : Prepara tion of L- thyroxine sodium/ cyclodextrin containing hydro¬ gels 8 ml of a 70 mg/ml solution of -cyclodextrin was stirred with 142 mg of thyroxine-Na to obtain a clear transparent solution. 150 mg of a water swellable polymer (i.e. Klucel; Hercules Corp. USA) was added. The mixture was ultrasonicated for 10 minutes and stirred for 3 hours to obtain a slight opalescent hydrogel. The stability of the hydrogel according to example 4 was found to be satisfactory over a storage period of two weeks at 25 °C Neither any precipitation in the gel nor decreasing of the con¬ tent of the solubilized thyroxine in the formulation was detec¬ ted. Example 5 : Preparation of L- thyroxine sodium/methyl -β-cyclodextrin containing hydrogels 10 ml of the 10 % aqueous randomly methylated-β-cyclodextrin solution was intensively stirred at 25 °C with 80 mg of L-thyr¬ oxine-Na for 4 hours to obtain a clear solution. To this solu¬ tion 250 mg of Klucel (Hercules Corp. USA) was added and ultra¬ sonicated for 10 minutes. The mixture was further stirred for 5 hours to obtain a transparent or slightly hazy hydrogel. The gel according to example 5 was found to be stable at 25 °C for two weeks, without precipitation or loss of the dissolved thyroxine content. Example 6 : Preparation of aqrueous topical gel containing L- thyroxine sodium / t -cyclodextrin The aqueous gel containing .^-cyclodextrin solubilized thyroxine was prepared by mixing at room temperature 150 mg of Pionier NP37 (polyacrylic acid) with 10 ml of 10 % aqueous ^-cyclo¬ dextrin solution containing 300 mg solubilized L-thyroxine-Na. The aqueous topically applicable formulation according to example 6 was a transparent, glassy gel. This gel can be stored in closed vials at room temperature for two weeks without signi¬ ficant decrease of the active ingredient or drug precipitation. Example 7 : Preparation of transdermal tape wi th L- thyroxine-Na/ methyl - cyclodextrin content 50 ml of 10 % aqueous heptakis-2, 6-di-O-methyl-β-cyclodextrin solution containing 9.5 mg/ml dissolved L-thyroxine sodium is mixed at 25 °C with 100 g of acrylic acid-2-ethylhexyl-acrylate copolymer and 0.1 g of preservative (sorbic acid) to obtain a clear or slightly opalescent gel that can directly be applied to a polyester foil and dried to give a transdermally applicable tape . Example 8 : Preparation of a transdermal therapeutic system containing L- thyroxine-Na/ "- cyclodextrin 500 μl of the formulation of example 6 are filled into a reser¬ voir patch consisting of a release liner, a backing foil, which is heat-sealed to a membrane that is coated with a pressure sen- sitive adhesive. Alternatively or additionally the reservoir sy¬ stem can have a peripherial adhesive ring. Example 9 : Preparation of thyroxine / ■ -cyclodextrin containing oral tablets The lyophilized, water-soluble formulation of thyroxine with J - cyclodextrin according to Example 1 having 20.1 % by weight of L-thyroxine sodium is mixed with common tabletting additives and compressed into tablets of 100 mg mass with an active ingredient content of 0.1 mg per tablet as described below: L-thyroxine/^-cyclodextrin complex lyophilisate 0.50 mg Avicel 52 mg Stearic acid 15 mg Aerosil R-972 12 mg Aerosil 300 3 mg Vinylpyrrolidone-vinyl-acetate copolymer 15 mg Maize starch 2.5 mg The same composition can be prepared by using kneaded L-thyr- oxine-Na/ ( f-cyclodextrin formulation according to Example 3. Example 10: Preparation of thyroxine /me thyl -β- cyclodextrin containing suppo- si tories Suppositories of 2 g mass with 0.1 mg active ingredient can be prepared from thyroxine/methyl-β-cyclodextrin lyophilized formu¬ lation according to example 2 in a known manner with the following composition: SUBSTITUTE SHEET (flULE 26) 0.108 g L-thyroxine/methylated β-cyclodextrin according to example 2 was added slowly to 200 g of the previously molten Massa estarinum and 100 suppositories were prepared from the composition. The content uniformity of the cyclodextrin com¬ plexed thyroxine in suppositories was found to be improved as a result of the inhibition of the migration of the thyroxine within the suppository base upon storage. Example 11: Jn vitro membrane permeation studies The comparison of the membrane permeation of free and cyclodextrin complexed L-thyroxine-Na from a Pionier NP37 based hydrogel showed that the formulation of the thyroxine with cyclodextrin results in a significantly improved membrane permeation through a cellulose-acetate membrane (Medicel Intl. Ltd. Dialysis Visking Tubing membrane 13-2") . The study was carried out at 37 °C in buffered media at pH 5.7 and the results of the membrane permeation study are listed in Table 2. Table 2 : Membrane permeation of free and ^-cyclodextrin com¬ plexed L-thyroxine-Na from a Pionier NP37 hydrogel according to example 6. time (minutes) dissolved L-thyrocine-Na in outer compartment (g/ml) Pionier NP37 Pionier NP37 thyroxine/ -cyclo- thyroxine dextrin complex 15 3.6 0 30 14.8 0 40 20.3 0 50 22.8 0 60 26.5 0. .7 80 31.8 3. 0 100 37.6 9. 1 120 38.9 11. 0 210 54.8 19. 1 240 57.3 24. 7 Example 12 : Physical stabili ty of aqueous topical gel according to example 6 10 ml of the aqueous Pionier NP37-thyroxine/^-cyclodextrin formulation was stored in sealed polyethylene bags as well as in capped glass vials under normal laboratory conditions (22 °C ex¬ posed to day light) for two weeks and the turbidity of the samples was investigated. After two weeks of storage no precipi¬ tate formation was visually observed. The total dissolved amount of L-thyroxine-Na was found to remain homogeneously distributed in the hydrogel after two weeks of storage. (The control gels containing the same amount of L-thyroxine-Na without cyclodextrin were all white, milky suspensions.) Also it is to be noted that clear aqueous ^-cyclodextrin solu¬ tions without any dissolved L-thyroxine-Na content turned to be hazy within three days, then after one week of storage a small amount of white precipitate formation occurred during storage. This phenomenon was not observed in case of L-thyroxine-Na/ - cyclodextrin containing hydrogels of Klucel or Pionier NP37. Example 13 Solubilization of L-thyroxine free acid form with f- cyclodextrin The aqueous solubility of the free acid form of L-thyroxine was found to be in the range of 0.11-0.15 mg/ml. This poor solu¬ bility can be affected positively by employing f- cyclodextrin . The effect of '-cyclodextrin as to the aqueous solubility of thyroxine acid is shown by the results in the table below: Table 3 : Aqueous solubility of thyroxine free acid in the presence of at 25 °C studied on two parallel experiments. concentration of ^-cyclodextrin solubility of thyroxine free acid in mg/ml (g/100 ml) 1-st run 2-nd run 0 0.110 0.150 5 0.400 0.379 10 0.646 0.652 12 0.765 0.800 15 1.02 1.00 20 1.39 1.44 As can be seen from the above data the aqueous solubility of the acid form of thyroxine can be enhanced by about ten- fold using - cyclodextrin in a concentration of 20 % by weight. Example 14 Prepara tion of L- thyroxine free acid/ ' "-cyclodextrin complex 0.54 g of /'-cyclodextrin and 0.137 g of L-thyroxine free acid were intensively co-grounded in 0.5 ml of 50 % (v/v) aqueous ethanol at room temperature for 30 minutes. The mixture was then allowed to dry at room temperature and sieved to obtain 0.532 g of white powdery solid L-thyroxine/ - cyclodextrin formulation. The formulation was analyzed for L- thyroxine acid content by UV spectrophotometry and it was found that the complex had 18.7 % of weight L-thyroxine acid. This formulation provides improved wettability and dissolution properties for the entrapped L-thyroxine acid.

Claims: Claims 1. Thyroxin/cyclodextrin formulation. 2. A thyroxin/cyclodextrin formulation according to claim 1, characterized by L-thyroxin or D-thyroxin or a free acid thereof or a pharmaceutically acceptable salt thereof, especially an alkali metal salt, preferably a sodium salt, or any racemate thereof . 3. A thyroxin/cyclodextrin formulation according to claim 1 or 2, characterized by cyclomaltooctaose (gamma-cyclodextrin) as cyclodextrin component . 4. A thyroxin/cyclodextrin formulation according to claim 3, characterized by a molar ratio range of gamma-cyclodextrin: thyroxin of from 25:1 to 0.5:1 and preferably 4:1 to 1:1. 5. A thyroxin/cyclodextrin formulation according to any of the preceding claims, viz. an L-thyroxin sodium/cyclodextrin formulation, especially an L-thyroxin sodium/gamma-cyclodextrin formulation. 6. A thyroxin/cyclodextrin formulation according to any of claims 1 to 2, characterized by randomly methylated β- cyclodextrin (RAMEB) having an average degree of substitution of from 1.6 to 2.5 and preferably 1.8 to 2 as cyclodextrin component. 7. A thyroxin/cyclodextrin formulation according to claim 6, characterized by a molar ratio range of RAMEB:thyroxin of from 25:1 to 0.5:1 and preferably 6:1 to 1:1. 8. A thyroxin/cyclodextrin formulation according to any of claims 1 to 2, characterized by heptakis-2, 6-di-O-methylated-β- cyclodextrin (DIMEB) having an average degree of substitution of from 1.6 to 2.5 and preferably 1.8 to 2.0 as cyclodextrin component. 9. A thyroxin/cyclodextrin formulation according to claim 8, characterized by a molar ratio range of DIMEB: thyroxin of from 25:1 to 0.5:1 and preferably 6:1 to 1:1. 10. Process for the production of a thyroxin/cyclodextrin formulation according to any of the preceding claims, characterized by kneading thyroxin and cyclodextrin in an amount of water which corresponds to the solubility of the formulation to be formed or which corresponds to up to twice the amount. 11. Thyroidal pharmaceutical composition, characterized by a content of a thyroxin/cyclodextrin formulation according to any of claims 1 to 9 as an active ingredient. 12. A thyroidal pharmaceutical composition according to claim 11, characterized by adjuvants and auxiliary agents usual for compositions for oral, transdermal, rectal or other parenteral applications . 13. A thyroidal pharmaceutical composition according to claim 11 or 12 for the treatment of hypothyroidism. 14. A thyroidal pharmaceutical composition according to claim 12 or 13, characterized in that the composition is a transdermal therapeutical system (TTS) comprising a reservoir containing a hydrogel (aqueous gel) . 15. A thyroidal pharmaceutical composition according to claim 14, characterized by a gel forming agent based on a polyacrylic acid or derivatives thereof. SUBSTTTUTE SHEET (RULE 26)

Inventors: BRACHER DANIEL, FISCHER WILFRIED, BRACHER, DANIEL, FISCHER, WILFRIED
Applicants: BRACHER DANIEL, FISCHER WILFRIED, HEXAL AG, BRACHER, DANIEL, FISCHER, WILFRIED
Application year: 1996
Main classification: A61K47
IPC codes: A61K9, A61K31, A61K47