emtricitabine

Emtricitabine is an antiretroviral medication in the class of nucleoside reverse transcriptase inhibitors (NRTIs). It is used to treat HIV-1 infection in combination with other antiretrovirals and is also used for HIV prevention through pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP). It is available as oral capsules and oral solution, and is commonly combined with tenofovir in fixed-dose products such as emtricitabine/tenofovir disoproxil fumarate (Truvada) and emtricitabine/tenofovir alafenamide (Descovy).

Mechanism of action: Emtricitabine is phosphorylated intracellularly to its active triphosphate form, which inhibits HIV-1 reverse transcriptase by competing with natural nucleotides and terminating DNA chain elongation after incorporation. It has activity against HIV-1 and, to a lesser extent, hepatitis B virus. Resistance can arise through mutations in reverse transcriptase. Common adverse effects include headache, nausea, diarrhea, rash, and hyperpigmentation of the palms or soles.

Administration and dosing: For treatment of HIV-1 infection, 200 mg of emtricitabine once daily is typical as part of combination therapy. For PrEP or PEP, it is used with a companion antiretroviral (most often tenofovir). Dose adjustments may be required in renal impairment; it should be used with caution in individuals with chronic hepatitis B infection who discontinue therapy due to potential HBV reactivation.

Safety and monitoring: Emtricitabine is generally well tolerated but can cause lactic acidosis and hepatic steatosis rarely. In HBV co-infected patients, stopping emtricitabine-containing regimens can lead to HBV reactivation. It is renally excreted, so dose adjustments may be needed in kidney impairment.