Emtricitabine

Absorption

Emtricitabine reaches a Cmax of 1.8±0.7μg/mL with a Tmax of 1-2 hours, and has an AUC of 10±3.1μg*hr/mL. The bioavailability of emtricitabine capsules is 93% and the bioavailability of the oral solution is 75%. Taking emtricitabine with food decreases the Cmax by 29%.[L9019

Toxicity

The LD50 of emtricitabine is not readily available.[9019,L9818]
Symptoms of emtricitabine toxicity include hepatotoxicity with steatosis, as well as lactic acidosis. Treat overdose with symptomatic and supportive measures, including hemodialysis.

Description

Emtricitabine is a synthetic nucleoside inhibitor of HIV-1 reverse transcriptase. Its mechanism of action entails the phosphorylation of the oxathiolane carbinol function by cellular enzymes to form the corresponding 5′-triphosphate, which competes with the endogenous 2′-deoxycytidine 5′-triphosphate substrate. The in vitro activity of emtricitabine ranges from IC₅₀ of 0.00013 to 0.64 mM against lymphoblastoid cell lines, MAGI-CCR5 cell lines, and peripheral blood mononuclear cells. Emtricitabine is prepared in about 16 steps from L-gulose, from which the O–C–S carbon stereochemistry is derived in the formation of substituted key 4-O-Acetyl-1,3- oxathiolane intermediate. This intermediate is coupled with N-benzoyl-O-trimethylsilyl- 5-fluoro-cytosine in the presence of trimethylsilyl triflate. The resulting anomeric mixture is separated by silica chromatography and subjected to two deprotection steps. Emtricitabine resistant isolates (M184V/I) were cross-resistant to lamivudine (desfluoro version of emtricitabine) and zalcitabine but remained sensitive to abacavir, didanosine, stavudine, tenofovir, zidovudine, and non-nucleoside reverse transcriptase inhibitors (delavirdine, efavirenz, and nevirapine). In a 48-week clinical trial using emtricitabine with didanosine and efavirin versus stavudine, didanosine and efavirenz produced 81 versus 68% responder rate respectively. In one study, 37.5% of treatment na?¨ve patients that were not achieving successful viral levels were found to exhibit a reduced potency toward emtricitabine. This resistance was due to M184V/I mutation in the HIV reverse transcriptase gene. Recommended dosing of emtricitabine is 200 mg (capsule) once per day. It is 93% bio-available and has a plasma half-life about 10 h, with 86% renal clearance. Side effects associated with emtricitabine treatment were generally mild to moderate and included headache, diarrhea, nausea, and rash. A generally mild and asymptomatic hyperpigmentation of the palms and/or soles was also observed.

The Uses of Emtricitabine

Labeled Emtricitabine, intended for use as an internal standard for the quantification of Emtricitabine by GC- or LC-mass spectrometry.

Background

Emtricitabine is a nucleoside reverse transcriptase inhibitor (NRTI) indicated for the treatment of HIV infection in adults or combined with tenofovir alafenamide for the prevention of HIV-1 infection in high risk adolescents and adults. Emtricitabine is a cytidine analogue. The drug works by inhibiting HIV reverse transcriptase, preventing transcription of HIV RNA to DNA.
Emtricitabine was granted FDA approval on 2 July 2003.

Indications

Emtricitabine is indicated in combination with other medications for the treatment of HIV-1 infections; treatment of HIV-1 infections in pediatric patients 25-35kg, treatment of HIV-1 infections in adult patients ≥35kg, for pre exposure prophylaxis of HIV-1 in adolescent and adult patients excluding those who have receptive vaginal sex; treatment of HIV-1 infections in pediatric and adult patients ≥17kg, pre exposure prophylaxis in adolescents and adults ≥35kg; treatment of HIV-1 in patients ≥12 years and ≥35kg; treatment of HIV-1 in patients weighing ≥35kg; treatment of HIV-1 in patients weighing ≥25kg; and treatment of HIV-1 in patients weighing ≥40kg.

What are the applications of Application

Emtricitabine is a HIV-1 reverse transcriptase (HIV-1 RT) inhibitor that can cause termination of DNA chain elongation in viruses.

Pharmacokinetics

Emtricitabine is a cytidine analog that competes with the natural substrate of HIV-1 reverse transcriptase to be incorporated into newly formed DNA, terminating its transcription. It is administered once daily so it has a long duration of action. Patients should be counselled regarding the risk of lactic acidosis and hepatomegaly with steatosis.

Metabolism

Emtricitabine is approximately 86% unmetabolized. Approximately 9% of a dose is metabolized to 3'-sulfoxide diastereomers, 4% to the 2'-O-glucuronide, and a minor amount is converted to 5-fluorocytosine.