Instability of Efavirenz Metabolites Identified During Method Development and Validation

Accurate quantification of efavirenz metabolites in patient samples is required to investigate their potential contribution to efavirenz adverse events. This study aimed to validate a LC-MS/MS method to quantify and investigate the stability of efavirenz and metabolites in human plasma. Compounds were extracted from plasma by supported liquid extraction and resolved on a C18 column. Validation was performed following FDA bioanalytical method validation guidelines. Stability under common conditions of sample pre-treatment and storage were assessed. Efavirenz and 8-hydroxyefavirenz were stable for all conditions tested. 7-Hydroxyefavirenz and 8,14-dihydroxyefavirenz were not stable in plasma at room temperature for 24 h (46%-69% loss), -20°C for 90 days (17%-50% loss), or 60°C for 1 h (90%-95% loss). Efavirenz and 8-hydroxyefavirenz concentrations in HIV/AIDS patient (n=5) plasma prepared from pre-treated (60°C for 1 h) whole blood varied from 517-8564 ng/mL and 131-813 ng/mL, respectively. 7-Hydroxyefavirenz and 8,14-dihydroxyefavirenz concentrations were below validated lower limits of quantification (0.25 and 0.5 ng/mL, respectively), most likely due to sample pre-treatment. This is the first report of 7-hydroxyefavirenz and 8,14-dihydroxyefavirenz instability under conditions commonly used in preparation of samples from HIV/AIDS patients. Alternative biosafety measures to heat pre-treatment must therefore be used for accurate quantification of plasma 7-hydroxyefavirenz and 8,14-dihydroxyefavirenz.