Simultaneous measurement of intracellular triphosphate metabolites of zidovudine, lamivudine and abacavir (carbovir) in human peripheral blood mononuclear cells by combined anion exchange solid phase extraction and LC–MS/MS

All nucleoside reverse transcriptase inhibitors (NRTI) must first be metabolized to their triphosphate forms in order to be active against HIV. Zidovudine (ZDV), abacavir (ABC) and lamivudine (3TC) have proven to be an efficacious combination. In order simultaneously to measure intracellular levels of the triphosphates (-TP) of ZDV, ABC (carbovir, CBV) and 3TC, either together or individually, we have developed a cartridge-LC–MS/MS method. The quantitation range was 2.5–250 pg/μl for 3TC-TP, 0.1–10.0 pg/μl for ZDV-TP and 0.05–5.00 pg/μl for CBV-TP. This corresponds to 0.1–11.0 pmol 3TC-TP per million cells, 4–375 fmol ZDV-TP per million cells and 2–200 fmol CBV-TP per million cells, extracted from 10 million cells. Patient samples demonstrated measured levels in the middle regions of our standard curves both at pre-dose and 4 h post-dose times.