Tenofovir and Emtricitabine Concentrations in Hair are Comparable between Individuals on Tenofovir Disoproxil Fumarate versus Tenofovir Alafenamide-based ART.

Tenofovir disoproxil fumarate (TDF) in combination with emtricitabine (FTC) is the backbone for both HIV treatment and PrEP worldwide. Tenofovir alafenamide (TAF) with FTC is increasingly used in HIV treatment and was recently approved for PrEP among men-who-have-sex-with-men. TDF and TAF are both metabolized into tenofovir (TFV). Antiretrovirals in plasma are taken up into hair over time, with hair levels providing a long-term measure of adherence. Here, we report a simple, robust, highly sensitive, and validated LC/MS/MS-based analytical method for analyzing TFV and FTC from individuals on either TDF/FTC or TAF/FTC in small hair samples. TFV/FTC are extracted from ~5 mg hair and separated on a column using a gradient elution. The lower quantification limits are 0.00200 (TFV) and 0.0200 (FTC) ng/mg hair; the assay is linear up to 0.0400 (TFV) and 0.400 (FTC) ng/mg hair. The intra- and inter-day CVs are 5.39-12.6% and 6.40-13.5% for TFV, and 0.571-2.45% and 2.45-5.16% for FTC. TFV concentrations from participants on TDF/FTC-based regimens with undetectable plasma HIV RNA were 0.0525±0.0295 ng/mg, whereas those from individuals on TAF/FTC-based regimens were 0.0426±0.0246 ng/mg. Despite the dose of TFV in TDF being 10 times that of TAF, hair concentrations of TFV were not significantly different for those on TDF- versus TAF-regimens. Pharmacological enhancers (ritonavir and cobicistat) did not boost TFV concentrations in hair. In summary, we developed and validated a sensitive analytical method to analyze TFV and FTC in hair and found that hair concentrations of TFV were essentially equivalent among those on TDF and TAF.