Evaluation of dried blood spots relative to peripheral blood mononuclear cells for intracellular tenofovir-diphosphate and emtricitabine-triphosphate assessment using liquid chromatography-tandem mass spectrometry.

Tenofovir alafenamide/emtricitabine (TAF/FTC) is widely used for HIV treatment and prevention. Their intracellular metabolites, tenofovir-diphosphate (TFV-DP) and emtricitabine-triphosphate (FTC-TP), provide informative measures of drug exposure. Peripheral blood mononuclear cells (PBMCs) are the primary matrix for these measurements; however, their isolation is labor-intensive, limiting clinical applicability. This study evaluated dried blood spots (DBS) for assessing intracellular TFV-DP and FTC-TP exposure relative to PBMCs. Paired PBMC and DBS samples (n = 124) were analyzed using a validated LC-MS/MS method. Moderate correlations were observed between DBS and PBMC concentrations for TFV-DP (r = 0.44, p < 0.0001) and FTC-TP (r = 0.27, p = 0.0025), with stronger correlations in the central 80% of participants based on the DBS-to-PBMC concentration ratios (r = 0.61 and 0.44, respectively). Log-transformed Bland-Altman analysis, with more than 90% of samples falling within the 95% limits of agreement. Additionally, concentration distributions across different virological statuses were similar between DBS and PBMC. DBS samples (n = 44) were also collected at baseline and on day 29 from people with HIV receiving TAF/FTC in combination with isoniazid plus rifapentine (1HP) to demonstrate the applicability of DBS for investigating potential drug-drug interactions (DDIs). In conclusion, the observed moderate correlations between DBS and PBMC concentrations of TFV-DP and FTC-TP suggest that DBS may serve as a feasible sampling approach for population-level assessment of intracellular TFV-DP and FTC-TP exposure. The simplicity of DBS sample collection and handling may facilitate large-scale clinical studies and highlights its potential utility in future clinical research.