Recommendations for Interpreting Intraerythrocytic Tenofovir Diphosphate and Emtricitabine Triphosphate for HIV-1 Preexposure Prophylaxis Adherence Assessment.

BACKGROUND

Intraerythrocytic tenofovir diphosphate (TFV-DP) and emtricitabine triphosphate (FTC-TP) in dried blood spots (DBS) have emerged as a gold-standard approach to assess adherence for oral preexposure prophylaxis (PrEP), but several considerations are important for proper interpretation.

METHODS

Key articles were reviewed related to use of intraerythrocytic TFV-DP and FTC-TP for adherence assessment including studies of pharmacokinetics, analytical methodologies, and application to a variety of PrEP settings. Important considerations were identified that influence TFV-DP and FTC-TP adherence interpretations by ≥15% and guidance was provided to assist when these considerations arise.

RESULTS

Factors identified included pregnancy status, specific drug interactions, hematocrit outside of 35%-50%, laboratory methodology, use of tenofovir alafenamide vs tenofovir disoproxil, whether DBS was collected before TFV-DP reaching steady state, and daily versus event-driven PrEP. Recommendations were provided in the form of adherence interpretation tables or mathematical adjustments to account for these considerations.

CONCLUSIONS

Proper interpretation of TFV-DP and FTC-TP in DBS requires accounting for the factors identified above to maximize the value of these measurements.