Differential extracellular and intracellular concentrations of zidovudine and lamivudine in semen and plasma of HIV-1-infected men

Objectives: To quantitate extracellular and intracellular zidovudine (ZDV) and lamivudine (3TC) concentrations in blood and semen of HIV-1-infected men. Design: Nonblind, single-center, open-label pharmacokinetic (PK) study in 14 subjects receiving ZDV plus 3TC. Methods: Paired blood and semen samples were obtained during I intensive visit and 3 single time point visits over 2 weeks. Extracellular ZDV and 3TC concentrations were measured in blood plasma (BP) and seminal plasma (SP), and intracellular ZDV and 3TC triphosphate (TP) concentrations were measured in isolated mononuclear cells using validated methods. HIV-1 RNA was measured in blood and semen. PK parameters were estimated using non-compartmental analysis. Results: Median (interquartile range [IQR]) SP/BP area under the time-concentration curve over the 12-hour dosing interval (AUC(0-12h)) ratios for ZDV and 3TC were 2.28 (1.48 to 2.97) and 6.67 (4.10 to 9.14), respectively, whereas individual SP/BP concentration ratios ranged from 1.9 to 91.4. Intracellular median (IQR) SP/BPAUC(0-12h) ratios for ZDV-TP and 3TC-TP were 0.36 (0.30 to 0.37) and 1.0 (0.62 to 1.30), respectively, whereas individual SP/BP concentration ratios ranged from 0.11 to 2.9. HIV-1 RNA was undetectable in both compartments. Conclusions: ZDV and 3TC SP exposures are 2- to 6-fold greater than BP exposures. Seminal ZDV-TP exposures are similar to 40% of those found in peripheral blood mononuclear cells (PBMCs), whereas 3TC-TP exposures are similar to PBMC exposures. PK variability makes individual SP/BP ratios a suboptimal surrogate for genital tract exposure.