Measurement of Antiretrovirals in Blood, Urine and Oral Fluids for Oral Preexposure Prophylaxis Adherence Monitoring

Abstract

The efficacy of daily oral pre-exposure prophylaxis (PrEP) significantly depends on maintaining sufficient drug concentrations from consistent and timely medication adherence. Therefore, oral PrEP adherence monitoring is essential to identify individuals with sub-optimal adherence who may benefit from enhanced support or intervention. Direct pharmacologic measurement of biological samples offers an accurate reflection of real-time drug concentrations, minimizing social desirability/recall bias associated with traditional adherence monitoring methods. Pharmacological measurements of PrEP adherence, like PrEP itself, are not one-size-fits-all. Different metrics measure various dimensions of PrEP adherence, such as dosing recency, dosing frequency, and cumulative dosing time. This dissertation, based on a randomized trial of emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) with directly-observed therapy (DOT), aimed to evaluate the feasibility and performance of measuring tenofovir diphosphate (TFV-DP) in blood; tenofovir (TFV) / emtricitabine (FTC) in oral fluids; and TFV in urine for PrEP adherence monitoring. We first assessed the associations between PrEP adherence (dosing recency, dosing frequence and cumulative dosing time) and drug concentrations of TFV-DP in dried blood spots (DBS), and estimated the steady-state adherence benchmarks for individuals with varying levels of adherence. Our findings indicated that the steady-state adherence benchmarks for TFV-DP concentrations in DBS were 466, 779, and 1375 fmol/3mm punch for participants taking 2, 4, and 7 doses per week, respectively. These benchmarks were slightly higher but comparable to previously established estimates. TFV-DP levels in DBS were associated cumulative dosing time, with each additional week of cumulative dosing leading to a 158 fmol/3mm punch increase (p<0.001) before achieving steady state. Next, we tested oral fluids for FTC/TFV to evaluate the relationships between drug concentrations and the three dimensions of PrEP adherence, and assessed the diagnostic performance of FTC/TFV in oral fluids for predicting PrEP non-adherence. Our findings suggested that FTC detectability in oral fluids is associated with dosing recency (odds ratio (OR): 0.21, 95% confidence interval (CI): 0.11-0.38). An FTC threshold of <7.5 ng/mL accurately classified 90% of recent PrEP non-adherence with one missed dose or more than 24 hours since the last dose. However, TFV was poorly diffused in oral fluids and its detectability was not associated with dosing recency, frequency, or cumulative dosing time. Lastly, we detected urine TFV concentrations using the next-gen urine TFV lateral flow assay (LFA) with quantified readouts. We assessed the effect of sex on the LFA readouts and calculated sex-specific sensitivities/specificities for recent non-adherence (defined as not having taken a dose within the prior 24 hours). Males exhibited a 33% lower peak color intensity (p<0.01) and a 1.82 unit lower averaged visual score of the LFA test line (p<0.01) compared to females. With the same optimal cutoffs for the LFA test/control line color intensity ratio (>0.095), we found similar sensitivities (93% vs. 93%) and specificities (99% vs. 94%) among males and females. Together, the results presented in this dissertation provide valuable insights into the potential applications of measuring antiretrovirals for daily oral PrEP adherence. Our work enhances understanding of the relationships between PrEP adherence and drug concentrations in different specimens. These new findings will help establish adherence benchmarks of drug concentrations and guide the development of future point-of-care (POC) tests for pharmacologic adherence monitoring and interventions.