Cobicistat

Inhibition of human cytochrome P450 activities is determined in duplicate in pooled human hepatic microsomal fractions following current scientific and regulatory guidelines. Reaction conditions are linear with respect to incubation time and hepatic microsomal protein concentration. Substrates are present at concentrations equal to or less than their respective K_m values determined under the same reaction conditions. Metabolite and/or substrate concentrations are determined using specific, internal standard controlled HPLC MS/MS assays. For reactions monitoring metabolite formation there is less than 20% consumption of substrate during the reaction. Unless otherwise noted microsomal fraction, diluted in potassium phosphate buffer, is preincubated with substrate and inhibitor for 5 min at 37 ℃ and the reaction initiated by the addition of an NADPH generating system followed by further incubation at 37 ℃ with shaking. Enzyme-selective positive control inhibitors are tested in parallel. At appropriate times aliquots of the mixture are removed and the reaction terminated by addition to a mixture of methanol and acetonitrile containing the respective internal standard. After centrifugation aliquots of the supernatant are subjected to HPLC-MS/MS analysis.