Simultaneous quantitation of zidovudine, efavirenz, lopinavir and ritonavir in human hair by liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry.

Nowadays, zidovudine, efavirenz, lopinavir and ritonavir are important components of the second-line antiretroviral therapeutic regimen of National Free Antiretroviral Treatment Program in China. The measurement of antiretroviral drugs in hair will facilitate for the evaluation of the long-term adherence to highly active antiretroviral therapy. Nevertheless, no study illustrated simultaneous quantitation of the four drugs in hair. The study intended to develop a simple, sensitive and selective method for simultaneous quantitation of the four drugs in hair. The detection employed high liquid chromatography tandem mass spectrometry with atmospheric pressure chemical ionization in positive mode. Hair samples were incubated in methanol at 40 °C for 16 h. The method showed the limit of detection at 18, 8, 5 and 6 pg/mg for zidovudine, efavirenz, lopinavir and ritonavir, respectively. The linear range (R > 0.99) was 36-5000 pg/mg for zidovudine, 16-5000 pg/mg for efavirenz, 10-50,000 pg/mg for lopinavir and 12-12,500 pg/mg for ritonavir. The intra-day and inter-day coefficients of variation were <15% and the recovery varied from 88.1 to 110.5%. The population analysis revealed that patients with high adherence showed significantly higher drug concentrations in hair than those with low adherence for both AZT and EFV (ps < 0.05). There was high association in drug contents in hair between AZT and EFV or LPV and RTV (ps < 0.05).