A pharmaceutical comparison of different commercially available imiquimod 5% cream products

Background: Alternatives to the innovator product for imiquimod 5% cream are currently marketed in South America and the People's Republic of China. Methods: Seven alternative imiquimod 5% cream products were compared with the innovator product using physiochemical tests for cream appearance, pH, drug content and presence of crystals, as well as in vitro release testing of drug using Franz diffusion cells. Results: In contrast to the innovator product, which had no crystalline imiquimod, significant amounts of suspended crystalline imiquimod were found in six of the seven alternative products. In vitro release rates of imiquimod were significantly slower in these six products compared with the innovator (p < 0.001). In vitro release rates of imiquimod were significantly faster than the innovator (p < 0.05) for the one alternative product without crystals. Conclusions: The clinical relevance of the differences observed is unknown; however, they raise concerns about whether these alternatives are therapeutically equivalent. While a generic topical imiquimod would almost certainly require clinical studies of therapeutic equivalence for approval in countries with more stringent regulatory environment, vigilance is warranted regarding importation of pharmaceutical products labeled as 'identical' in the absence of adequate evaluations.