Examining Hair to Determine Tenofovir Exposure

Inclusion Criteria: * Ability to speak English * HIV-1 uninfected, based on HIV rapid testing performed during screening and enrollment * Calculated creatinine clearance greater than or equal to 60 mL/min by the Cockcroft-Gault creatinine clearance formula * Serum creatinine less than or equal to the site laboratory upper limit of normal * Urine dipstick with negative or trace result for both glucose and protein * Negative urine beta human chorionic gonadotropin (beta-HCG) test for women * Adequate hepatic function, defined as total bilirubin and hepatic transaminases (ALT and AST) less than or equal to twice the upper limit of normal * Adequate hematologic function, defined as an absolute neutrophil count greater than or equal to 1,500/mm3, platelet count greater than or equal to 100,000/mm3, and hemoglobin greater than or equal to 10 g/dL * Ability to participate in modified directly observed dosing of study drug * Ability to provide a personal cell phone number to be contacted on for unobserved modified directly observed therapy (mDOT) visits * Minimum length of 3 cm scalp hair in occipital region * Willing to provide hair and plasma samples as specified by the protocol * Dark hair (brown or black), as assessed by the study clinician * Volunteers born female must agree to consistently use effective contraception from at least 21 days prior to enrollment through the last protocol visit for sexual activity that could lead to pregnancy and agree not to seek pregnancy through alternative methods, such as artificial insemination or in vitro fertilization until after the last scheduled protocol visit. Exclusion Criteria: * Active and serious medical problems, including heart or lung disease, diabetes requiring hypoglycemia medications, previously diagnosed malignancies expected to require further treatment, and serious infections * Hepatitis B surface antigen positivity * History of chronic kidney disease * Known osteoporosis, osteomalacia, or osteopenia * History of pathological bone fractures not related to trauma * Receiving ongoing therapy with any of the following: antiretroviral therapy, interferon or interleukin therapy, aminoglycoside antibiotics, amphotericin B, cidofovir, systemic chemotherapeutic agents, other agents with significant nephrotoxic potential, other agents that may inhibit or compete for elimination via active renal tubular secretion (e.g., probenecid), or other investigational agents * Evidence of a gastrointestinal malabsorption syndrome or chronic nausea or vomiting that may confer an inability to receive an orally administered medication * Use of hair dyes or hair permanent products in the last 3 months (streaking is acceptable) * Current participation in any other research study involving drugs, investigational agents, or medical devices * Breastfeeding at screening or enrollment, per participant report * Active alcohol or drug use considered sufficient by clinician to hinder compliance with study procedures * Elevated risk of HIV infection, as defined in the study protocol * At enrollment, has any social or medical condition that, in the investigator's opinion, would preclude provision of informed consent, make participation in the study unsafe, complicate interpretation of study outcome data, or otherwise interfere with achieving the study objectives