Developing a discriminating dissolution test for three mebendazole polymorphs based on solubility differences.

Mebendazole, a broad spectrum anthelmintic drug, is practically insoluble in water and exists in three polymorphic forms, A, B, and C, of which C is pharmaceutically favoured. Since the dissolution of drugs from solid oral dosage forms can depend on the crystal form of the drug an attempt should be made while developing dissolution tests to set test parameters that are sensitive to changes in the crystal form. USP 24 describes 0.1 M hydrochloric acid containing 1.0% sodium lauryl sulphate (SLS) as the dissolution medium for mebendazole tablets. Results showed that the high concentration of sodium lauryl sulphate in the USP dissolution medium does not allow the use of this test to distinguish between the solubility differences of the three mebendazole polymorphs. By decreasing the amount of sodium lauryl sulphate in the dissolution medium clear differences in the dissolution rates of the three forms were observed. The most discriminating medium was 0.1 M HCl, containing no sodium lauryl sulphate.