Tenofovir-Emtricitabine

• HIV Treatment
• HIV Pre-Exposure Prophylaxis (PrEP)
• HIV Prevention

Tenofovir disoproxil fumarate combined with emtricitabine, sold as Truvada, is a fixed-dose combination of two nucleoside/nucleotide reverse transcriptase inhibitors used both for the treatment of HIV-1 infection (in combination with other antiretrovirals) and for HIV pre-exposure prophylaxis (PrEP) in adults and adolescents at risk of sexually acquired HIV. Approved by the FDA for treatment in 2004 and for PrEP in 2012, this combination has fundamentally changed both the management of HIV and the prevention landscape for at-risk individuals, including men who have sex with men, transgender individuals, sex workers, and HIV-serodiscordant couples. The combination is also a backbone of many global treatment regimens because of its potency, tolerability, once-daily dosing, and broad availability as generics. Patients prescribed this medication should understand its absolute requirement for confirmed HIV-negative status when used as PrEP, the need for hepatitis B testing before initiation, and the importance of ongoing monitoring of kidney and bone health.

Mechanism of Action

Both components target HIV reverse transcriptase, the viral enzyme responsible for converting viral RNA into proviral DNA, an essential step in the HIV life cycle. Tenofovir disoproxil fumarate is an oral prodrug rapidly hydrolyzed in plasma to tenofovir, an adenosine 5'-monophosphate analog. After cellular uptake, tenofovir is phosphorylated by host kinases to its active form, tenofovir diphosphate. This molecule competes with deoxyadenosine 5'-triphosphate for incorporation into the growing viral DNA chain; when incorporated, it terminates further DNA elongation because it lacks the 3'-hydroxyl group required for the next nucleotide addition.

Emtricitabine is a cytidine analog phosphorylated intracellularly to emtricitabine 5'-triphosphate, which similarly competes with deoxycytidine 5'-triphosphate and serves as a chain terminator. The two drugs work at different positions of the HIV genome and have non-overlapping resistance mutation profiles, providing synergistic antiviral activity. Both drugs have prolonged intracellular half-lives, supporting once-daily dosing. Importantly, both are also active against hepatitis B virus, which is why hepatitis B status must be assessed before initiation; abrupt discontinuation in HBV-coinfected patients can precipitate a flare. A newer formulation, tenofovir alafenamide combined with emtricitabine (Descovy), is a prodrug designed to deliver tenofovir more efficiently to lymphoid tissue with lower plasma exposure, resulting in less kidney toxicity and bone density loss; Descovy is approved for HIV treatment and for PrEP in men who have sex with men and transgender women. Comprehensive guidance is available from the Centers for Disease Control and Prevention.

Clinical Use

For HIV treatment, tenofovir-emtricitabine combined with an integrase strand-transfer inhibitor (such as dolutegravir) or a boosted protease inhibitor (such as darunavir plus ritonavir or cobicistat) forms a complete antiretroviral regimen. Single-tablet regimens containing tenofovir plus emtricitabine plus a third agent, such as bictegravir-emtricitabine-tenofovir, have largely replaced multi-pill combinations in initial therapy because of their simplicity and tolerability.

For PrEP, tenofovir-emtricitabine is taken daily by adults and adolescents weighing at least 35 kg who test HIV-negative and have ongoing risk of sexual or injection-related exposure. Studies including iPrEx, Partners PrEP, and TDF2 demonstrated reductions in HIV acquisition of more than 90 percent with high adherence. Maximum protective levels are reached in rectal tissue after approximately 7 days of daily dosing and in cervicovaginal tissue after about 20 days. Off-label event-driven (or 2-1-1) dosing is used in some settings for men who have sex with men but is not FDA-approved in the United States.

Patient selection for PrEP includes confirmed negative HIV test, willingness to attend regular monitoring visits (typically every 3 months), normal baseline kidney function, hepatitis B surface antigen status documented, and counseling about adherence, ongoing risk reduction, and other prevention strategies. Patients must continue safer-sex practices and undergo testing for other sexually transmitted infections regularly. Pregnant women with HIV use tenofovir-emtricitabine as a preferred backbone given extensive safety data, often combined with dolutegravir or another preferred third agent. Our internal medicine team works closely with infectious disease colleagues to coordinate PrEP and HIV care.

How to Take It

The standard dose is one tablet (300 mg tenofovir disoproxil fumarate / 200 mg emtricitabine) once daily, taken with or without food. Consistency of timing improves adherence; pairing the dose with a daily anchor activity such as brushing teeth or breakfast helps. The tablet should be swallowed whole. If a dose is missed and remembered within 12 hours, take it as soon as possible. If more than 12 hours have passed, skip that dose and take the next dose at the regular time; do not double up.

For PrEP, perfect adherence matters more than for some chronic medications because the protective drug levels in genital and rectal tissues depend on near-daily dosing. Missing a single dose occasionally is unlikely to compromise protection, but recurrent missed doses substantially reduce efficacy. Patients should report any missed doses to the clinician and consider strategies such as phone alarms, weekly pillboxes, or pharmacy text reminders. Storage is at room temperature in the original bottle. The first week may bring mild gastrointestinal symptoms (nausea, diarrhea, headache, fatigue) that usually subside within 1 to 2 weeks. Persistent vomiting, dark urine, decreased urine output, severe muscle weakness, or rapid breathing warrants immediate evaluation. Patients should not stop the medication without consulting the prescriber, especially if they have hepatitis B coinfection, because abrupt discontinuation can precipitate a hepatitis flare.

Monitoring and Follow-Up

For PrEP, baseline assessment includes HIV-1 antibody/antigen testing (must be negative), creatinine and eGFR, hepatitis B surface antigen, hepatitis C antibody, and STI panel including syphilis, gonorrhea, and chlamydia at appropriate anatomic sites. Pregnancy testing for women of reproductive potential is performed. Follow-up visits occur at 1 month, then every 3 months, with HIV testing, creatinine, and STI screening; pregnancy testing as needed. Hepatitis B status is reassessed if the patient has had potential exposures or vaccination is in progress.

For HIV treatment, monitoring also includes HIV-1 RNA viral load, CD4 count, complete blood count, comprehensive metabolic panel, fasting lipids, and urinalysis. Initial intensive monitoring (every 4 to 8 weeks) eventually transitions to every 3 to 6 months with sustained virologic suppression. Red flags include eGFR decline of more than 25 percent from baseline (consider switching to tenofovir alafenamide), persistent proteinuria or glycosuria (suggesting tubular injury), AST or ALT elevation more than 3 times baseline (suggesting hepatitis flare or other liver injury), unexplained weight loss, persistent muscle weakness or pain (rare lactic acidosis), or new fragility fracture. Bone mineral density testing is appropriate in patients with risk factors for osteoporosis and certainly in patients on long-term tenofovir disoproxil who fracture. Detailed FDA labeling is available at accessdata.fda.gov.

Special Populations

In renal impairment, tenofovir disoproxil fumarate requires dose interval extension: every 48 hours for creatinine clearance 30 to 49 mL/min, and the combination is not recommended for clearance below 30 mL/min, including hemodialysis. Patients with progressive renal decline often transition to a tenofovir alafenamide-based regimen. No specific hepatic dose adjustment is required, but caution and close monitoring are warranted in patients with significant hepatitis B coinfection. Pregnancy: tenofovir disoproxil fumarate is among the most extensively studied antiretrovirals in pregnancy and is preferred for both treatment and PrEP. It does not increase rates of major birth defects, preterm birth, or low birth weight in available cohorts.

Lactation in HIV-positive mothers in the United States is generally not recommended due to the risk of HIV transmission, although in resource-limited settings exclusive breastfeeding while on suppressive therapy is preferred to formula feeding. Adolescents weighing at least 35 kg may use the adult dose for both treatment and PrEP. Pediatric formulations are available for younger patients. Patients with hepatitis B coinfection require ongoing tenofovir-based therapy with careful monitoring; abrupt discontinuation has caused fatal hepatic decompensation. Patients with significant osteoporosis or risk factors should have bone density and vitamin D status assessed, and tenofovir alafenamide may be the better choice. Concomitant nephrotoxic drugs, including aminoglycosides, vancomycin, foscarnet, and high-dose NSAIDs, should be avoided when possible.

When to Contact Your Doctor

Call the office promptly for symptoms suggesting acute kidney injury (decreased urine output, swelling, dark urine, severe fatigue), unexplained muscle weakness or pain (could indicate proximal renal tubular injury or, rarely, lactic acidosis), bone pain or unexplained fracture, abdominal pain with nausea (potentially pancreatitis), jaundice, dark urine, or right upper abdominal pain (potentially hepatitis flare or hepatotoxicity), and rapid breathing or severe fatigue. Symptoms of severe allergic reaction including rash, swelling of the face or tongue, and difficulty breathing require emergency care. New or worsening bone pain in the hips, back, or feet warrants evaluation.

For PrEP users, any potential HIV exposure (condom failure, missed doses around exposure, sexual assault) should prompt urgent contact for evaluation and possibly post-exposure prophylaxis. Pregnancy or planned pregnancy should be discussed; the regimen is generally compatible with pregnancy but other prevention strategies and counseling should be reviewed. Symptoms of acute HIV infection (fever, sore throat, lymphadenopathy, rash, severe fatigue) in a PrEP user should prompt urgent HIV testing because resistance can develop if PrEP is continued during seroconversion. For HIV prevention or treatment evaluation, contact us or schedule a visit. Detailed dosing tables, drug interactions, and frequently asked questions are provided on this page below.