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LiverTox: Clinical and Research Information on Drug-Induced Liver Injury [Internet]. Bethesda (MD): National Institute of Diabetes and Digestive and Kidney Diseases; 2012-.

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LiverTox: Clinical and Research Information on Drug-Induced Liver Injury [Internet].

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Emtricitabine

Last Update: February 10, 2018.

OVERVIEW

Introduction

Emtricitabine is a nucleoside analogue and reverse transcriptase inhibitor used in combination with other agents for treatment and prevention of human immunodeficiency virus (HIV) infection and the acquired immunodeficiency syndrome (AIDS). Emtricitabine does not appear to be a significant cause of drug induced liver injury, but may cause flares of disease in patients with underlying chronic hepatitis B virus (HBV) infection.

Background

Emtricitabine (em" trye sye' ta been) is an L-enantiomer and substituted analogue of cytosine (5-fluorothiocytidine: FTC) and is active against both HIV and HBV, being similar in structure and activity to lamivudine. Emtricitabine is intracellularly phosphorylated to emtricitabine 5’-triphosphate which competes with the naturally occurring deoxycytidine 5’-triphosphate for incorporation into HIV DNA by the HIV reverse transcriptase, resulting in chain termination and inhibition of the polymerase activity. Emtricitabine was approved for use in HIV infection in the United States in 2006. Current indications include treatment of HIV infection, the prophylaxis of HIV infection in cases of occupational exposure, nonoccupational exposure, and perinatal transmission. Emtricitabine is also active against HBV, but has not been specifically approved for use in hepatitis B. The combination of emtricitabine with tenofovir is used in many current antiretroviral regimens and is considered the therapy of choice in patients with HBV-HIV coinfection. Emtricitabine is available as 200 mg capsules and in an oral solution as a single agent under the brand name of Emtriva; in 200 mg tablets in combination with tenofovir disoproxil fumarate (300 mg) as Truvada; in tablets in combination with tenofovir (300 mg) and efavirenz (600 mg) as Atripla; and in capsules in combination with tenofovir (300 mg), elvitegravir (150 mg) and cobicistat (150 mg) as Stribild. The recommended dose of emtricitabine in adults is 200 mg orally once daily. The combination formulations of Truvada, Atripla and Stribild are also given orally once daily. Side effects of attributable to emtricitabine are uncommon.

Hepatotoxicity

There is little evidence for direct hepatotoxicity of emtricitabine and it has not been specifically implicated in cases of lactic acidosis with steatosis and hepatic failure. However, patients with chronic hepatitis B can experience a flare of the underlying hepatitis during emtricitabine therapy. These flares occur either at the start therapy (treatment flares), with the development of antiviral resistance (breakthrough flares), or when therapy is abruptly stopped (withdrawal flares). Treatment flares occur in 5% to 10% of patients, are usually transient and asymptomatic, and rarely require dose modification or discontinuation of therapy. In contrast, withdrawal flares occur in 15% to 30% of patients, but can be symptomatic and severe, in rare instances (~1%) leading to acute liver failure, death or requirement for emergency liver transplantation. Patients who develop emtricitabine resistance often have relapse of disease activity after the appearance of the mutant HBV strain and rise in HBV DNA levels; this relapse can initially be severe and associated with symptoms and jaundice.

Mechanism of Injury

The apparent absence of significant hepatotoxicity from emtricitabine may be due to its minimal hepatic metabolism (13%) and the fact that it is both an L-enantiomer of cytidine and is blocked at the 3’ position on the deoxyribose component, making it unlikely that emtricitabine would be used by host nuclear or mitochondrial polymerases. The flares of hepatitis B that occur with initiation, antiviral resistance or withdrawal of therapy probably represent activation of immune responses to HBV caused by the sudden change in levels of viral replication.

Outcome and Management

ALT elevations have not been associated with emtricitabine use in patients without hepatitis B. Patients with HBV infection who have a flare of disease during emtricitabine can usually be monitored carefully and continued on therapy. Patients with a flare of hepatitis due to development of antiviral resistance should be switched to or have the addition of another agent with a different profile of resistance. Patients with a withdrawal flare of hepatitis B should be evaluated rapidly and restarted on antiviral therapy, if appropriate. Cases of acute liver failure requiring liver transplantation have been reported in patients with hepatitis B withdrawn from emtricitabine therapy. Due to the correlation between HIV/HBV coinfection and liver dysfunction in a subset of patients who discontinue emtricitabine, all patients with HIV should be tested for HBV before starting therapy with emtricitabine.

Agents used in therapy of HBV infection include adefovir, emtricitabine, entecavir, lamivudine, telbivudine, tenofovir, interferon alfa and peginterferon.

Drug Class: Antiviral Agents, Antiretroviral Agents, Hepatitis B Agents

Other Drugs in the Subclass, Nucleoside Analogues: Abacavir, Adefovir, Didanosine, Entecavir, Lamivudine, Stavudine, Telbivudine, Tenofovir, Zidovudine

PRODUCT INFORMATION

REPRESENTATIVE TRADE NAMES

Emtricitabine – Emtriva®

DRUG CLASS

Antiviral Agents

COMPLETE LABELING

Product labeling at DailyMed, National Library of Medicine, NIH

CHEMICAL FORMULA AND STRUCTURE

DRUGCAS REGISTRY NUMBERMOLECULAR FORMULASTRUCTURE
Emtricitabine 143491-57-0 C8-H10-F-N3-O3-S
Emtricitabine Chemical Structure

ANNOTATED BIBLIOGRAPHY

References updated: 10 February 2018

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  • Squillace N, Ricci E, Quirino T, Gori A, Bandera A, Carenzi L, De Socio GV, et al.; CISAI Study Group. Safety and tolerability of elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil fumarate in a real life setting: data from surveillance cohort long-term toxicity antiretrovirals/antivirals (SCOLTA) project. PLoS One 2017; 12 (6): e0179254. [PMC free article: PMC5478131] [PubMed: 28632758]
    (Among 280 patients with HIV infection started on therapy with elvitegravir/cobicistat, emtricitabine and tenofovir and monitored for a median of 11 months, serum enzyme elevations occurred in 23 subjects [8%], but most were less than 5 times the upper limit or normal and only 3 led to treatment interruptions).
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    (Prospective surveillance of maternity hospitals in Botswana and 47,027 live births found that adverse outcomes were more common among HIV-exposed than unexposed infants [40% vs 29%], and rates were lower in those whose mothers were taking emtricitabine and tenofovir based- vs lamivudine [47%] or zidovudine [45%] based-regimens, and lower with efavirenz vs nevirapine containing regimens [36% vs 42%] and were lowest of all in those on these regimens since the time of conception [12% and 18%]).
  • Orkin C, Molina JM, Negredo E, Arribas JR, Gathe J, Eron JJ, Van Landuyt E,et al.; EMERALD study group. Efficacy and safety of switching from boosted protease inhibitors plus emtricitabine and tenofovir disoproxil fumarate regimens to single-tablet darunavir, cobicistat, emtricitabine, and tenofovir alafenamide at 48 weeks in adults with virologically suppressed HIV-1 (EMERALD): a phase 3, randomised, non-inferiority trial. Lancet HIV 2018; 5: e23-e34. [PubMed: 28993180]
    (Among 1141 treatment experienced adults with HIV infection who were maintained on their regular regimen or switched to a single-table formulation of darunavir, cobicistat, emtricitabine and tenofovor alafenamide and followed for 48 weeks, virologic success was similar in the two groups [95% vs 94%] as were overall and serious adverse event rates including renal dysfunction, liver enzyme elevations and osteopenia; marked fasting LDL cholesterol elevations were more frequent with the single tablet compared to control regimen [7% vs 2%]).

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