Emtricitabine
Emtricitabine (FTC) is a nucleoside reverse transcriptase inhibitor (NRTI) and one of the most commonly prescribed antiretrovirals. It is rarely used alone — it is a backbone component of the fixed-dose combinations Truvada, Descovy, Atripla, Biktarvy, Genvoya, Odefsey, Symtuza, and Stribild. It also has activity against hepatitis B virus (HBV), which is critically important when considering discontinuation.[1]
Administration
- Type: Nucleoside reverse transcriptase inhibitor (NRTI); cytidine analog
- Dosage Forms: 200 mg capsules; 10 mg/mL oral solution
- Routes of Administration: Oral
- Common Trade Names: Emtriva; most commonly encountered in fixed-dose combinations: Truvada (FTC/TDF), Descovy (FTC/TAF), Atripla (FTC/TDF/EFV), Biktarvy (FTC/TAF/bictegravir), Genvoya, Odefsey, Symtuza, Stribild
Adult Dosing
- Capsules: 200 mg PO once daily[1]
- Oral solution: 240 mg (24 mL) PO once daily
- May take with or without food
- Most patients receive emtricitabine as a component of a fixed-dose combination tablet rather than standalone
Pediatric Dosing
- Approved from birth[1]
- Capsules (≥33 kg): 200 mg PO once daily
- Oral solution (children ≥3 months): 6 mg/kg PO once daily (max 240 mg)
- Neonates (birth to <3 months): 3 mg/kg PO once daily
Special Populations
Pregnancy Rating
- No adequate controlled studies; APR data show no increased birth defect risk (2.3% vs. 2.7% background)[1]
- Crosses the placenta; widely used in pregnancy as part of preferred NRTI backbone
- Antiretroviral Pregnancy Registry: 1-800-258-4263
Lactation risk
- Present in human milk; women with HIV should discuss risks and benefits of breastfeeding with their provider[1]
Renal Dosing
- Adult (primarily renally eliminated; dose adjustment required):[1]
- CrCl 30–49 mL/min: 200 mg capsule every 48 hours (or 120 mg oral solution once daily)
- CrCl 15–29 mL/min: 200 mg capsule every 72 hours (or 80 mg oral solution once daily)
- CrCl <15 mL/min or hemodialysis: 200 mg capsule every 96 hours (or 60 mg oral solution once daily); administer after dialysis on dialysis days
- Hemodialysis removes ~30% of emtricitabine dose over a 3-hour session[1]
- Pediatric: No specific data; consider similar adjustments based on CrCl
Hepatic Dosing
- Adult: No dose adjustment needed (not hepatically metabolized)[1]
- Pediatric: No adjustment needed
Contraindications
- Allergy to class/drug
- Do not coadminister with lamivudine-containing products (therapeutic duplication — both are cytidine analogs with overlapping resistance profiles)[1]
Adverse Reactions
Serious
- Hepatitis B flare (Boxed Warning): Severe, acute exacerbations of HBV (including liver decompensation and failure) reported in HIV/HBV co-infected patients who discontinue emtricitabine. Monitor hepatic function closely for at least several months after stopping[1]
- Lactic acidosis with hepatic steatosis (NRTI class effect; including fatal cases)[1]
- Immune reconstitution inflammatory syndrome (IRIS)
Common
- Headache, diarrhea, nausea, fatigue, dizziness, insomnia, abnormal dreams[1]
- Rash (generally mild)
- Hyperpigmentation of palms and soles (primarily in patients of African descent; up to 2–3%; more common in children)[2]
- Elevated CK, transaminases
Pharmacology
- Half-life: ~10 hours (plasma); intracellular triphosphate half-life ~39 hours (supports once-daily dosing)[1]
- Metabolism: Minimal; not a CYP450 substrate and does not inhibit or induce CYP enzymes[1]
- Excretion: ~86% urine (~13% as metabolites, ~70% unchanged), ~14% feces. Elimination by both glomerular filtration and active tubular secretion[1]
Mechanism of Action
Emtricitabine is a cytidine analog that is intracellularly phosphorylated to its active form, emtricitabine 5'-triphosphate. This competes with the natural substrate deoxycytidine 5'-triphosphate for incorporation by HIV-1 reverse transcriptase. Once incorporated, it terminates the growing DNA chain due to the lack of a 3'-hydroxyl group. Emtricitabine triphosphate is a weak inhibitor of mammalian DNA polymerases α, β, ε, and mitochondrial DNA polymerase γ, giving it a favorable mitochondrial toxicity profile compared to older NRTIs.[1]
Comments
- Hepatitis B flare — the #1 ED pearl: Emtricitabine has anti-HBV activity. If an HIV/HBV co-infected patient stops any emtricitabine-containing regimen (Truvada, Descovy, Biktarvy, Atripla, etc.) — whether intentionally, due to lapsed insurance, incarceration, or nonadherence — they are at risk for a severe hepatitis B flare that can present as acute liver failure. Check HBV serologies and LFTs in any HIV patient presenting with jaundice or transaminase elevation after recent ARV discontinuation[1]
- Lamivudine duplication: Emtricitabine and lamivudine (3TC) are structurally and functionally interchangeable — never combine them. Verify the medication list to avoid duplication (e.g., a patient on Biktarvy should not also receive lamivudine)[1]
- Almost no drug interactions: Emtricitabine is not CYP450-metabolized and does not affect levels of other drugs. It is one of the safest ARVs from an ED prescribing standpoint — virtually no downstream interaction concerns[1]
- Renal dosing required: Unlike many ARVs, emtricitabine is primarily renally cleared and requires dose adjustment at CrCl <50 mL/min. Be aware that fixed-dose combinations (Truvada, Descovy, Biktarvy, etc.) have their own renal thresholds and may not be appropriate for patients with significant renal impairment
- Hyperpigmentation: Painless discoloration of palms/soles, predominantly in patients of African descent — not harmful but can cause patient concern. Do not mistake for other dermatologic conditions
- Overdose: No specific antidote; supportive care. Hemodialysis removes ~30% of drug over 3 hours[1]
See Also
- HIV - AIDS (main)
- HIV post-exposure prophylaxis
- Immune reconstitution syndrome
- Emtricitabine/tenofovir