Tenofovir diphosphate and emtricitabine triphosphate concentrations in blood cells compared with isolated peripheral blood mononuclear cells: a new measure of antiretroviral adherence?

BACKGROUND The active metabolites of tenofovir (TFV) and emtricitabine (FTC) in peripheral blood mononuclear cells (PBMCs) have been used as markers of long-term antiretroviral (ARV) adherence. However, the process of isolating PBMCs is expensive, complex, and not feasible in many settings. We compared concentrations of TFV-diphosphate (TFV-DP) and FTC-triphosphate (FTC-TP) in the upper layer packed cells (ULPCs) obtained after whole blood centrifugation to isolated PBMCs as a possible alternative marker of adherence. METHODS Ten HIV+ adults with HIV RNA <50 copies/mL on a TDF/FTC-containing regimen provided 5 paired PBMC and ULPC samples over 6 hours. TFV-DP and FTC-TP concentrations were analyzed by liquid chromatography/mass spectrometry. Partial areas under the curve were calculated using noncompartmental methods and Spearman Rank Correlations (rho) between PBMC and ULPC were determined. RESULTS The median (25th-75th percentile) concentration of TFV-DP in PBMCs was 143 (103-248) fmol/10(6) cells and in ULPC was 227 (160-394) fmol/10(6) cells (rho = 0.65; P < 0.0001). The concentration of FTC-TP in PBMCs was 6660 (5650-10,000) fmol/10(6) cells and in ULPC was 19.0 (12.0-27.8) fmol/10(6) cells (rho = 0.55; P < 0.0001). Compared to PBMCs, ULPC TFV-DP was 64% higher and FTC-TP was 99.7% lower. ULPC concentrations of TFV-DP and FTC-TP in one additional subject receiving a single dose of TDF/FTC were only 0.05% and 25%, of the other 10 subjects, respectively. CONCLUSIONS ULPC concentrations significantly correlated with PBMC concentrations. Preliminary single-dose data suggest some discrimination between intermittent versus consistent dosing. ULPC concentrations of TFV-DP and FTC-TP should be further investigated as a simply collected surrogate measure of ARV adherence.