CARBOPLATIN COMPOSITION

Abstract: A carboplatin composition is provided in the form of an aqueous solution of carboplatin buffered at a pH of 2-6.5. Such a ready to use solution possesses a remarkable stability.

Description: Carboplatin is a known cytostatic agent. Up till now, this agent was marketed as a freeze-dried product and accordingly it is reconstituted before administration. Of course, a ready to use solution would be a much more advantageous composition, but carboplatin is not stable in a simple aqueous solution. As has appeared by research, carboplatin can decompose through various mechanisms, whereby a.o. the highly poisonous compounds di-µ-hydroxo-bis(cis-diammineplatinum (II)), and tri-µ-hydroxo-tris(cis-diammineplatinum (II)) can be formed. It has now been found that a solution buffered in a certain pH range is sufficiently stable to be used as carboplatin composition. Accordingly, the invention provides a carboplatin composition which is characterized by the fact that it has the form of an aqueous solution of carboplatin which has been buffered at a pH of 2-6.5. In the upper part of the above mentioned range the stability is acceptable, but it is even better at a somewhat lower pH. Furthermore, the injection of the solution is of course more disagreeable, the lower the pH is. Consequently, the solution is preferably buffered at a pH of 2.5-4.5 and more preferably at a pH of 3.1-3.5. The maximum solubility of the carboplatin is about 22 mg/ml. The concentration of the preparation of the present invention can be adjusted arbitrarily up to this limit; usually a therapeutical concentration is used of 8-12 mg/ml, particularly around 10 mg/ml. One can use any buffering agent, for instance those mentioned in Handbook of Chemistry and Physics, 58th Edition, pages D-133 to D-135. For practical reasons one can suitably use a phosphate buffer, with which, as is well known, the pH can be adjusted within a very broad range. It is preferred to have the lowest possible buffer concentration which however, should have sufficient buffering capacity. Generally, a strength of the buffer of about 0.01-0.03 M will suffice. For completeness' sake it is remarked that from EP-A-0 275 559 a cytostatic agent on the basis of carboplatin is known, which has a specific distribution of particle sizes and is prepared according to a very special process. From this powdery product injectable solutions can be made, but according to page 4, lines 31-34 these solutions should contain further adjuvants and should be made up immediately before use. The same appears from the last paragraph of example 4 of this publication. The following, non-limiting example further elucidates the present invention. A series of carboplatin solutions having a concentration of 10 mg/ml was prepared with the following buffers and pH-values: 1: Carboplatin in 0.01 M sodium-di-hydrogen phosphate, pH 2.5 with phosphoric acid. 2-1: Carboplatin in 0.01 M sodium-di-hydrogen phosphate, pH 3.5 with phosphoric acid. 2-2: Carboplatin in 0.10 M sodium-di-hydrogen phosphate, pH 3.5 with phosphoric acid. 2-3: Carboplatin in 0.50 M sodium-di-hydrogen phosphate, pH 3.5 with phosphoric acid. 3: Carboplatin in 0.01 M sodium-di-hydrogen phosphate, pH 4.5 with phosphoric acid. 4: Carboplatin in 0.01 M di-sodium-hydrogen phosphate, pH 5.5 with phosphoric acid. 5: Carboplatin in 0.01 M di-sodium-hydrogen phosphate, pH 6.5 with phosphoric acid. 6: Carboplatin in 0.01 M di-sodium-hydrogen phosphate, pH 7.5 with sodium hydroxide. The above mentioned solutions were stored during 1, 2, 3 and 4 months under the following conditions: A 0-8°C B 20-22°C (room temperature) C 40°C The pH of each solution was measured and the contents of carboplatin and decomposition products were determined by liquid chromatography. This was done with the solution as originally prepared, and after 1, 2, 3 and 4 months. The results are given in the following tables. For the sake of brevity the contents of decomposition products has been indicated therein as "by-peaks". It appears from the above results that a too high concentration of buffering agent has an adverse influence on the stability (solution 2-3). For the rest the solutions appear to be well stable in the pH range up to and inclusive 6.5, even at 40°C.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, DK, FR, GB, IT, LI, LU, NL, SE Carboplatin composition, characterized by the fact that it has the form of an aqueous solution of carboplatin, which has been buffered at a pH of 2-6.5. Carboplatin composition according to claim 1, characterized by the fact that it has been buffered at a pH of 2.5-4.5. Carboplatin composition according to claim 2, characterized by the fact that it has been buffered at a pH of 3.1-3.5. Carboplatin composition according to any of the previous claims, characterized by the fact that the buffering agent is a phosphate buffer. Carboplatin composition according to any of the previous claims, characterized by the fact that the buffer has a concentration of 0.01-0.03 M. Carboplatin composition according to any of the previous claims, characterized by the fact that the carboplatin concentration is 8-12 mg/ml. Claims for the following Contracting States : ES, GR A process for preparing a carboplatin composition, characterized by preparing an aqueous solution of carboplatin, buffered at a pH of 2-6.5. A process according to claim 1, characterized by buffering the solution at a pH of 2.5-4.5. A process according to claim 2, characterized by buffering the solution at a pH of 3.1-3.5. A process according to any of the previous claims, characterized by using as the buffering agent a phosphate buffer. A process according to any of the previous claims, characterized by using the buffer in a concentration of 0.01-0.03 M. A process according to any of the previous claims, characterized by preparing a solution having a carboplatin concentration of 8-12 mg/ml.

Inventors: NIJKER, ALFRED JAMES, VERMEER, JOHANNA MARIA PIETERNELLA
Applicants: PHARMACHEMIE B.V.
Application year: 1990
Main classification: A61K31
IPC codes: A61K47, A61K9, A61K33, A61P35, A61K31