Emtricitabine and Tenofovir

Emtricitabine and tenofovir is an antiviral combination approved for two major uses across supported products:

• HIV-1 treatment: Truvada is approved to treat HIV-1 infection in adults and pediatric patients weighing at least 17 kg, always used with other antiretroviral drugs. Descovy is approved to treat HIV-1 infection in adults and in pediatric patients weighing at least 14 kg (in combination with other antiretrovirals, including darunavir and cobicistat but not other ritonavir- or cobicistat-boosted protease inhibitors for the lower weight ranges).
• HIV-1 Pre-Exposure Prophylaxis (PrEP): Truvada is approved to reduce the risk of sexually acquired HIV-1 in HIV-negative adults at high risk, used alongside safer-sex practices. Descovy is approved for HIV-1 PrEP in HIV-negative individuals weighing at least 35 kg.
• Neither Truvada nor Descovy is approved for treating chronic hepatitis B virus (HBV) infection.

Emtricitabine and tenofovir are both classified as nucleoside analog reverse transcriptase inhibitors (NRTIs). HIV needs an enzyme called reverse transcriptase to convert its genetic material into a form it can use to replicate inside human cells. Both drugs mimic the natural building blocks of DNA but act as dead ends — when HIV tries to use them, viral replication is blocked. Without the ability to copy itself efficiently, the virus cannot spread through the body.

Because HIV can mutate and develop resistance, these drugs are used with other antivirals for HIV treatment. For PrEP, maintaining consistent daily drug levels is critical — clinical trials showed effectiveness was strongly tied to how reliably the medication was taken.

Emtricitabine and tenofovir tablets are taken once daily by mouth. Both Truvada and Descovy can be taken with or without food, though previous safety and efficacy trials for tenofovir disoproxil fumarate were conducted under fed conditions. Your prescriber will select the right strength based on your weight, kidney function, and whether you are using it for HIV treatment or PrEP.

• For PrEP use, HIV testing is required immediately before starting and at least every 3 months during treatment.
• If kidney function is reduced, dosing frequency may need to change or the medication may not be appropriate — follow your prescriber's guidance carefully.
• Never stop taking this medication on your own, especially if you also have hepatitis B — stopping suddenly can cause a severe hepatitis B flare.

The most common side effects reported in HIV-1-infected adults include:

• Diarrhea
• Nausea
• Headache
• Fatigue
• Dizziness
• Depression or low mood
• Trouble sleeping or vivid/abnormal dreams
• Skin rash

In people taking Truvada for PrEP, headache, abdominal pain, and mild weight loss were reported more often than with placebo. More seriously, changes in kidney function and bone density can occur over time — which is why regular lab monitoring is required. Contact your doctor right away if you notice signs of kidney problems (decreased urination, swelling) or unexpected bone pain.

• Lactic acidosis (acid buildup in the blood): This rare but life-threatening complication has been reported with nucleoside analog antivirals. Watch for unusual muscle weakness, belly pain, nausea, vomiting, cold extremities, or trouble breathing — get emergency care immediately.
• Severe hepatomegaly with steatosis (liver swelling with fat buildup): Also rare and potentially fatal; may occur alongside lactic acidosis.
• Hepatitis B flare after stopping: In people who also have hepatitis B, stopping this medication can trigger a sudden, severe worsening of hepatitis B. Liver function must be monitored closely for at least several months after stopping.
• Kidney problems: New or worsening kidney impairment, including acute kidney failure and Fanconi syndrome (a kidney tubule disorder), can occur. Baseline and ongoing kidney function tests are required. Avoid combining with other drugs that are hard on the kidneys.
• Bone density loss: Decreases in bone mineral density have been observed, especially in pediatric patients. Assessment of bone density may be recommended in those at risk for fractures.
• Drug resistance with PrEP: If someone is unknowingly infected with HIV when they start taking this for PrEP, drug-resistant HIV can develop. Confirmed HIV-negative status is required before and during PrEP use.
• Immune reconstitution syndrome: As the immune system recovers during HIV treatment, it may mount a strong inflammatory response to previously hidden infections, requiring further evaluation.

Several important drug interactions exist with emtricitabine and tenofovir — always tell your prescriber and pharmacist everything you take:

• Didanosine (ddI): Tenofovir raises didanosine levels significantly, increasing the risk of pancreatitis, nerve damage, and suppressed immune cell counts — dose reduction and close monitoring are required.
• Atazanavir: Tenofovir lowers atazanavir blood levels; atazanavir must be paired with ritonavir when used together.
• Certain HIV protease inhibitors (lopinavir/ritonavir, ritonavir-boosted atazanavir, ritonavir-boosted darunavir): These raise tenofovir levels, increasing the risk of tenofovir-related kidney and bone side effects.
• Hepatitis C drugs (sofosbuvir/velpatasvir, sofosbuvir/velpatasvir/voxilaprevir, ledipasvir/sofosbuvir): These can also raise tenofovir concentrations; monitoring for toxicity is needed.
• Other kidney-cleared drugs (acyclovir, ganciclovir, aminoglycoside antibiotics, high-dose NSAIDs): May increase levels of emtricitabine, tenofovir, or the co-administered drug.
• Duplicate ingredient products (Atripla, Complera, Emtriva, Genvoya, Odefsey, Stribild, Viread, lamivudine-containing drugs, Hepsera): Do not combine — overlapping ingredients can cause overdose or serious harm.

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Unknown or positive HIV status: Do not use for PrEP if you are HIV-positive or your HIV status is unknown — this can lead to drug-resistant HIV.
• Hepatitis B infection: Tell your doctor before starting; stopping the medication can trigger a severe hepatitis B flare, and liver function must be monitored.
• Kidney disease: Kidney function must be assessed before and during treatment; reduced kidney function may require dose changes or mean the medication is not appropriate.
• Bone health concerns: Those with a history of bone fractures or osteoporosis risk factors should discuss bone density monitoring with their doctor.
• Pregnancy: Discuss risks and benefits with your doctor. Observational data have not shown an increased rate of major birth defects. A pregnancy registry (1-800-258-4263) is available. For women at risk of HIV during pregnancy, continuing or initiating PrEP may be considered.
• Breastfeeding: Mothers with HIV-1, or suspected HIV-1, should not breastfeed due to the risk of transmitting HIV to the infant.
• Older adults: The pharmacokinetics of emtricitabine and tenofovir have not been fully studied in people 65 and older; use with care.
• Children: Truvada is approved for pediatric patients weighing at least 17 kg for HIV treatment; Descovy has weight-based criteria for pediatric use. PrEP use in adolescents has specific weight requirements.

If too much of this medication is taken, the person should be monitored for signs of toxicity and given supportive medical care. Limited data exist on very high doses of either component, and no severe reactions were reported in small studies of higher-than-usual doses. Tenofovir can be partially removed by hemodialysis (a blood-filtering procedure), and emtricitabine is also partially removed by hemodialysis.

After taking emtricitabine and tenofovir by mouth, emtricitabine is absorbed quickly, with peak blood levels reached within 1 to 2 hours. Tenofovir reaches peak levels in about 1 hour. Both drugs are cleared mainly through the kidneys — a combination of filtration and active secretion — so reduced kidney function significantly affects how the body handles them.

Emtricitabine has a half-life (the time for blood levels to drop by half) of about 10 hours, while tenofovir's half-life is approximately 17 hours. These tablets can be taken with or without food; food slightly increases tenofovir exposure but does not meaningfully affect emtricitabine levels.

Store at 25 °C (77 °F), excursions permitted to 15 °C–30 °C (59 °F–86 °F) (see USP Controlled Room Temperature).