Urine tenofovir and emtricitabine concentrations provide biomarker for exposure to HIV preexposure prophylaxis

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Clinical trials of preexposure prophylaxis (PrEP) using antiretroviral medications have demonstrated success in preventing HIV infection among at-risk populations. Oral PrEP regimens containing the nucleotide and nucleoside reverse transcriptase inhibitors tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) are highly effective among adherent study participants [1–4]. Studies of dosing patterns from clinical trials indicate increased PrEP efficacy is associated with greater adherence to oral daily dosing regimens [5,6]. However, measuring adherence for persons taking oral PrEP regimens is challenging and has relied primarily on self-report [7]. Laboratory methods of determining adherence to antiretroviral drug regimens involve mass spectrometry analyses of accumulated drug metabolites in hair or blood specimens [8,9]. These assays provide reliable measures of cumulative drug exposure predictive of protection against HIV, yet are technologically complex and expensive. The availability of rapid, inexpensive, and noninvasive methods to assess adherence to PrEP regimens would allow for opportunities to provide timely feedback regarding individual adherence. TDF and FTC are metabolized and excreted primarily in urine [10], and urine tenofovir (TFV) has recently been used to indicate PrEP adherence in an individual using chewed Truvada (TDF/FTC) [11]. Therefore, we sought to determine whether urine might provide a specimen type amenable to development of noninvasive methods to measure PrEP drug exposure.

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