Analyses of marketplace tacrolimus drug product quality: bioactivity, NMR and LC-MS.

Tacrolimus (FK506) is a potent, narrow therapeutic index, immunosuppressive drug used to avoid organ rejection in patients that have undergone organ transplantation. Recent clinical reports suggested a significant reduction in the tacrolimus concentration/dose ratio in the plasma of liver and kidney recipients when the reference listed drug was substituted with a generic drug. In response to these concerns about switching between tacrolimus from different approved manufacturers during treatment, the FDA initiated purity, potency and quality studies of the innovator and generic tacrolimus products available in the US marketplace. A combination of analytical methods, including mass spectrometry (LC-MS), nuclear magnetic resonance (NMR) and bioactivity assay were developed and validated to assess the quality of tacrolimus. These tests measured the identity, impurities and activity of tacrolimus from active pharmaceutical ingredient (API) sources and with formulated drug product from five different approved manufactures. In addition, some testing was performed on tacrolimus capsules obtained from a non US approved Indian source. The data obtained showed no discernible difference in the impurity profiles and potency between the generic and innovator tacrolimus products.