Ver el código de «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 [[Emtricitabine/tenofovir|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.<ref name="EmtrivaPI">Emtriva (emtricitabine) [prescribing information]. Foster City, CA: Gilead Sciences, Inc.; 2018.</ref>

==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/[[Efavirenz|EFV]]), Biktarvy (FTC/TAF/bictegravir), Genvoya, Odefsey, Symtuza, Stribild

==Adult Dosing==
*'''Capsules:''' 200 mg PO once daily<ref name="EmtrivaPI"/>
*'''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<ref name="EmtrivaPI"/>
*'''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==
===[[Drug pregnancy categories|Pregnancy Rating]]===
*No adequate controlled studies; APR data show no increased birth defect risk (2.3% vs. 2.7% background)<ref name="EmtrivaPI"/>
*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<ref name="EmtrivaPI"/>

===Renal Dosing===
*Adult (primarily renally eliminated; dose adjustment required):<ref name="EmtrivaPI"/>
**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<ref name="EmtrivaPI"/>
*Pediatric: No specific data; consider similar adjustments based on CrCl

===Hepatic Dosing===
*Adult: No dose adjustment needed (not hepatically metabolized)<ref name="EmtrivaPI"/>
*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)<ref name="EmtrivaPI"/>

==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<ref name="EmtrivaPI"/>
*'''Lactic acidosis with hepatic steatosis''' (NRTI class effect; including fatal cases)<ref name="EmtrivaPI"/>
*[[Immune reconstitution syndrome|Immune reconstitution inflammatory syndrome (IRIS)]]

===Common===
*Headache, diarrhea, nausea, fatigue, dizziness, insomnia, abnormal dreams<ref name="EmtrivaPI"/>
*Rash (generally mild)
*'''Hyperpigmentation''' of palms and soles (primarily in patients of African descent; up to 2–3%; more common in children)<ref name="Wiki">Emtricitabine. ''Wikipedia''. Accessed 2025.</ref>
*Elevated CK, transaminases

==Pharmacology==
*Half-life: ~10 hours (plasma); intracellular triphosphate half-life ~39 hours (supports once-daily dosing)<ref name="EmtrivaPI"/>
*Metabolism: Minimal; not a CYP450 substrate and does not inhibit or induce CYP enzymes<ref name="EmtrivaPI"/>
*Excretion: ~86% urine (~13% as metabolites, ~70% unchanged), ~14% feces. Elimination by both glomerular filtration and active tubular secretion<ref name="EmtrivaPI"/>

==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.<ref name="EmtrivaPI"/>

==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<ref name="EmtrivaPI"/>
*'''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)<ref name="EmtrivaPI"/>
*'''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<ref name="EmtrivaPI"/>
*'''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<ref name="EmtrivaPI"/>

==See Also==
*[[HIV - AIDS (main)]]
*[[HIV post-exposure prophylaxis]]
*[[Immune reconstitution syndrome]]
*[[Emtricitabine/tenofovir]]

==References==
{{reflist|2}}
[[Category:Pharmacology]]