Emtricitabine

Emtricitabine (FTC), with trade name Emtriva (formerly Coviracil), is a nucleoside reverse transcriptase inhibitor (NRTI) for the treatment of HIV infection in adults and children.

Emtricitabine is also marketed in a fixed-dose combination with tenofovir (Viread) under the brand name Truvada. A fixed-dose triple combination of emtricitabine, tenofovir and efavirenz (Sustiva, marketed by Bristol-Myers Squibb) was approved by the U.S. Food and Drug Administration (FDA) on July 12, 2006 under the brand name Atripla.

History
Emtricitabine was discovered by Dr. Dennis C. Liotta, Dr. Raymond Schinazi and Dr. Woo-Baeg Choi of Emory University and licensed to Triangle Pharmaceuticals by Emory in 1996. Triangle Pharmaceuticals was acquired in 2003 by Gilead Sciences, who completed development and now market the product with the brand name Emtriva.

It was approved by the FDA July 2, 2003. It is very similar to lamivudine (3TC) and cross-resistance between the two is near-universal.

Mode of action
Emtricitabine is an analogue of cytidine. The drug works by inhibiting reverse transcriptase, the enzyme that copies HIV RNA into new viral DNA. By interfering with this process, which is central to the replication of HIV, emtricitabine can help to lower the amount of HIV, or "viral load", in a patient's body and can indirectly increase the number of immune system cells (called T cells or CD4+ T-cells). Both of these changes are associated with healthier immune systems and decreased likelihood of serious illness.

HIV infection
Emtricitabine is indicated in combination with other antiretroviral agents for the treatment of HIV infection in adults. Emtricitabine is commercially available and is approved by the FDA for treatment of HIV infection.

HBV infection
Emtricitabine exhibits clinical activity against the hepatitis B virus (HBV). Among individuals with chronic HBV infection, emtricitabine treatment results in significant histologic, virologic, and biochemical improvement. The safety profile of emtricitabine during treatment is similar to that of a placebo. Emtricitabine, however, cures neither HIV nor HBV infection. In a study involving individuals with HBV infection, symptoms of infection returned in 23% of emtricitabine-treated individuals who were taken off therapy. In studies involving individuals with chronic HIV infection, viral replication also resumes when study subjects are taken off therapy. Emtricitabine is not approved by the FDA for treatment of HBV infection. As with drugs used to treat HIV infection, drugs used to treat HBV infection may have to be used in combination to prevent the evolution of drug resistant strains. Lamivudine is also active against HBV virus and commercially available. Like emtricitabine, lamivudine, when used on its own, does not completely suppress viral replication. This allows drug resistant strains to emerge. The effectiveness of emtricitabine in combination with other anti-HBV drugs has not been established. Clinical trials are still ongoing.

Side effects
In clinical practice, toxicity with emtricitabine is unusual. The most common treatment-related adverse events are diarrhea, headache, nausea, and rash. These symptoms are generally mild to moderate in severity, but they caused 1% of clinical trial patients to give up treatment. Skin discoloration, which is typically reported as hyperpigmentation and usually affects either the palms of the hands or the soles of the feet, is reported in less than 2% of individuals and is almost exclusive to patients of African origin.

Among the more severe side effects patients may experience are a hepatotoxicity or a lactic acidosis.