Measurement of efavirenz and its metabolites

Drug assays were performed at two laboratories. The analytical laboratory in the Division of Clinical Pharmacology at the University of Cape Town quantified total efavirenz in plasma and CSF using validated LC/MS-MS assays. The lower limit of quantification (LLOQ) for plasma and CSF efavirenz was 19.5 and 0.5 ng/mL, respectively. The Bioanalytical Facility, Department of Molecular and Clinical Pharmacology at the University of Liverpool quantified total CSF 8-hydroxy-efavirenz, plasma 8-hydroxy-efavirenz and plasma 7-hydroxy-efavirenz using validated LC/MS-MS assays.22 We could not quantify CSF 7-hydroxy-efavirenz. The LLOQ for CSF 8-hydroxy-efavirenz, plasma 8-hydroxy-efavirenz and plasma 7-hydroxy-efavirenz was 3.125 ng/mL, 5.0 ng/mL and 5.0 ng/mL, respectively. Concentrations below the limit of quantification were analysed as missing data.