Development, validation and clinical implementation of a UPLC-MS/MS bioanalytical method for simultaneous...

A reversed phase ultra-high performance liquid chromatography method was developed for the simultaneous quantification of cabotegravir (CAB) and the E-isomer of rilpivirine (RPV) in human EDTA plasma, also considering RPV E-isomer instability. Because of the instability of RPV (and CAB) in all light conditions, the (RPV Z-isomer/total RPV)-isomer ratio of RPV was determined for each stock, calibration curve standard, quality control sample and patient sample. [²H₃]-CAB and [¹³C₆]-RPV were used as internal standard. Sample preparation involved protein precipitation of plasma using methanol. An HSS T3 column with a guard column (set at 40 °C) was used for analyte separation. The mobile phase components were 65 % 0.1 % formic acid in water (A) and 35 % 0.1 % formic acid in acetonitrile (B) and the flow rate was 0.5 mL/min. Detection was performed with tandem mass spectrometry (MS/MS) in a total runtime of 3.0 min. The assay was validated over the concentration range of 0.0500 - 10.0 mg/L for CAB and 0.00300 - 3.00 mg/L for RPV. The average within-day and between-day accuracies for the assay in plasma were 101 % and 101 % for CAB and 97.6 % and 98.5 % voor RPV, respectively. Within-day and between-day precision in coefficients of variations (CV) were 5.0 %. Extraction recovery was 99 % and 102 % for CAB and its internal standard and 95 % and 97 % for RPV and its internal standard. As our aim was that the (Z-isomer RPV/total RPV) response ratio in patient samples had to be less than 10 % to give reliable results, the (Z-isomer RPV/total RPV) response ratio in stocks, calibration curve standards and internal quality control samples were also taken into account being maximal 0.9 % and 2.3 % respectively. This assay has been successfully used in our Therapeutic Drug Monitoring (TDM) service for people living with HIV on long-acting injectable therapy with CAB/RPV and will also be used in future pharmacokinetic studies.