Emtricitabine: Indications, Mechanism of Action and Side Effects

Indications

Emtricitabine（FTC） is a nucleoside reverse transcriptase inhibitor (NRTI) used in combination with other antiretroviral therapies for treating HIV-1, HIV-2, and HBV. It is FDA-approved for HIV treatment but not for HBV. Emtricitabine (Emtricitabine / Tenofovir Disoproxil Fumarate, Truvada) is also part of the combined drug used for PrEP to prevent HIV infection, indicated for individuals at high risk such as those with HIV-positive partners or inconsistent condom use. It is safe for pregnant women and those with concurrent HCV infection. Additionally, emtricitabine is used as part of PEP following potential HIV exposure, recommended within 72 hours and for a 28-day duration. It is commonly included in the combination pill for PEP therapy due to its fewer side effects.

Mechanism of Action

Emtricitabine is a cytidine analogue that belongs to the nucleoside reverse transcriptase inhibitor (NRTI) class of drugs.Emtricitabine generally exerts its therapeutic effect by phosphorylating into an active substance, emtricitabine 5'-triphosphate, which in turn binds to the HIV reverse transcriptase enzyme in the viral DNA and disrupts the synthesis of HIV DNA. Emtricitabine 5‘-triphosphate competes with deoxycytidine 5’-triphosphate for HIV-1 reverse transcriptase, causing HIV-1 reverse transcriptase to incorporate it into the resulting DNA strand, preventing the incorporation of new nucleotides and resulting in the termination of the viral DNA strand. Without reverse transcriptase, HIV cannot replicate in the body. Blocking reverse transcriptase helps to reduce HIV viral load and increase the number of CD4+ T cells.

Side Effects

Common side effects of Emtricitabine include: headache, muscle weakness, joint pain, fatigue, fever, abdominal pain, nausea, vomiting, diarrhoea, depression, anxiety, insomnia, rhinitis, cough and pharyngitis. A significant skin effect associated with emtricitabine is skin pigmentation, especially on the palms of the hands and soles of the feet, which is more pronounced in African Americans. Other possible side effects are skin discolouration that can occur on the tongue, arms, lips and nail beds. Emtricitabine is generally well tolerated and has not been found to be associated with serious adverse events, but you need to contact your doctor promptly if you experience any serious adverse symptoms that affect your life or life.

When emtricitabine is combined with tenofovir in the formulation Truvada, particularly for pre-exposure prophylaxis (PrEP), similar gastrointestinal symptoms, headaches, nausea, and depressive symptoms are observed. Long-term use (2-3 years) may lead to a decrease in creatinine clearance, with improvements seen upon discontinuation. While initial declines in glomerular filtration rate (GFR) can occur, they tend to stabilize over time, and severe renal dysfunction has not been reported. However, patients over 40 may experience noticeable changes in GFR. Additionally, Truvada can lead to decreased bone mineral density, which normalizes after stopping the medication, without an increased risk of fractures. Serious side effects of Truvada include lactic acidosis, liver issues, and worsening kidney problems, which necessitate immediate medical attention. Symptoms of lactic acidosis include unusual muscle pain, shortness of breath, and dizziness, while liver issues may present as jaundice and abdominal pain. Lastly, patients with coexisting HIV and hepatitis B should be cautious, as stopping Truvada may exacerbate HBV infection.

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