Factors associated with tenofovir diphosphate concentrations in dried blood spots in persons living with HIV.

Objectives: To determine factors associated with interindividual variability in tenofovir diphosphate (TFV-DP) concentrations in dried blood spots (DBSs) among persons living with HIV (PLWH). Methods: PLWH who were at least 18years old and taking tenofovir disoproxil fumarate-containing ART were prospectively recruited and enrolled from a clinical cohort and followed longitudinally (up to three visits over 48weeks). With log-transformed TFV-DP concentrations in DBSs as the outcome, mixed-model regression analyses were used to assess associations between self-reported 3month ART adherence, race and other clinical covariates (gender, age, BMI, CD4+ T cell count, estimated glomerular filtration rate, haematocrit, duration on current ART and anchor drug class) on TFV-DP in DBSs. Results: Five hundred and twenty-seven participants (1150 person-visits) were analysed. Adjusting for race and other clinical covariates, every 10% increase in self-reported 3month ART adherence was associated with an average TFV-DP concentration increase in DBSs of 28% (95% CI: 24%-32%; P<0.0001). In the same model, female participants had 20% (95% CI: 3%-40%; P=0.02) higher TFV-DP concentrations in DBSs, compared with male participants, and every 1kg/m(2) increase in BMI was associated with a decrease in TFV-DP concentration in DBSs by 2% (95% CI: -3% to -1%; P<0.0001). Conclusions: Individual patient characteristics were predictive of TFV-DP concentration in DBSs in PLWH receiving tenofovir disoproxil fumarate-based ART. Future research to incorporate these predictors into the interpretation of this ART adherence biomarker, and to establish whether these associations extend to PLWH taking tenofovir alafenamide-containing ART, is needed.