{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,25]],"date-time":"2026-02-25T02:55:40Z","timestamp":1771988140843,"version":"3.50.1"},"reference-count":84,"publisher":"Wiley","issue":"7","license":[{"start":{"date-parts":[[2021,4,13]],"date-time":"2021-04-13T00:00:00Z","timestamp":1618272000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"funder":[{"DOI":"10.13039\/100000060","name":"National Institute of Allergy and Infectious Diseases","doi-asserted-by":"publisher","award":["2R01AI098472"],"award-info":[{"award-number":["2R01AI098472"]}],"id":[{"id":"10.13039\/100000060","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["analyticalsciencejournals.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Drug Testing and Analysis"],"published-print":{"date-parts":[[2021,7]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>Tenofovir disoproxil fumarate (TDF) in combination with emtricitabine (FTC) is the backbone for both human immunodeficiency virus (HIV) treatment and pre\u2010exposure prophylaxis (PrEP) worldwide. Tenofovir alafenamide (TAF) with FTC is increasingly used in HIV treatment and was recently approved for PrEP among men\u2010who\u2010have\u2010sex\u2010with\u2010men. 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\u2010term measure of adherence. Here, we report a simple, robust, highly sensitive, and validated high\u2010performance liquid chromatography coupled with tandem mass spectrometry (LC\/MS\/MS)\u2010based 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\u00a0mg 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 0.400 (TFV) and 4.00 (FTC) ng\/mg hair. The intra\u2010day and inter\u2010day coefficients of variance (CVs) are 5.39\u201312.6% and 6.40\u201313.5% for TFV and 0.571\u20132.45% and 2.45\u20135.16% for FTC. TFV concentrations from participants on TDF\/FTC\u2010based regimens with undetectable plasma HIV RNA were 0.0525\u2009\u00b1\u20090.0295\u2009ng\/mg, whereas those from individuals on TAF\/FTC\u2010based regimens were 0.0426\u2009\u00b1\u20090.0246\u2009ng\/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.<\/jats:p>","DOI":"10.1002\/dta.3033","type":"journal-article","created":{"date-parts":[[2021,3,20]],"date-time":"2021-03-20T07:56:31Z","timestamp":1616226991000},"page":"1354-1370","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Tenofovir and emtricitabine concentrations in hair are comparable between individuals on tenofovir disoproxil fumarate versus tenofovir alafenamide\u2010based ART"],"prefix":"10.1002","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8519-7409","authenticated-orcid":false,"given":"Hideaki","family":"Okochi","sequence":"first","affiliation":[{"name":"Division of HIV, Infection Diseases, and Global Medicine, Department of Medicine University of California San Francisco  San Francisco 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