A method employing SPE, MRM LC-MS/MS and a THF–water solvent system for the simultaneous determination of five antiretroviral drugs in human blood plasma

A multiple reaction monitoring liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method for the simultaneous determination of five antiretroviral drugs i.e. emtricitabine, tenofovir, efavirenz, lopinavir and ritonavir using commercially sterilized human blood plasma as the matrix and a THF/water solvent system was developed for therapeutic drug monitoring purposes and partially validated using the United States Food and Drug Administration (US FDA) guidelines. The analytical performance characteristics that were examined were limits of detection (LODs), lower limits of quantification (LLOQs), upper limits of quantification (ULOQs), selectivity, percent mean recoveries, precision measured as percent relative standard deviations and accuracy. Optimized LC-MS/MS parameters were employed for this purpose. The percent mean recoveries were between 77.3 and 90.1% using solid phase extraction (SPE) for sample preparation. These recoveries were obtained at three spike levels i.e. the LOD, the LLOQ and the ULOQ. The precision of the SPE technique was within an acceptable range of <15% i.e. between 2.7 and 9.2% at the LLOQ. Accuracy was calculated as the percent deviation of the mean value from the true value and the values ranged between 9.9 and 22.7%. The SPE technique satisfied all the requirements of the US FDA guidelines except for efavirenz whose accuracy was slightly higher than recommended at the LLOQ i.e. 22.7% as opposed to 20%. The limits of detection using SPE also fell below the clinically relevant therapeutic range (3–8 mg L−1) for most of the drugs and therefore the method could be useful for therapeutic drug monitoring in HIV patients.