Emtricitabine

Usage

Emtricitabine is an antiretroviral medication, specifically a nucleoside/nucleotide reverse transcriptase inhibitor (NRTI), primarily used in combination with other antiretroviral agents for the treatment of Human Immunodeficiency Virus type 1 (HIV-1) infection in adults and children. It is also used, in combination with tenofovir disoproxil fumarate, as pre-exposure prophylaxis (PrEP) to reduce the risk of sexually acquired HIV-1 in high-risk individuals. It is not a cure for HIV or AIDS. Emtricitabine works by blocking the reverse transcriptase enzyme, which HIV needs to replicate.

Alternate Names

Emtricitabine is also known as FTC. Brand names for emtricitabine alone include Emtriva. Emtricitabine is available in combination with other drugs in various fixed-dose combinations (FDCs), under brand names such as Atripla, Biktarvy, Complera, Descovy, Genvoya, Odefsey, Stribild, Symtuza, and Truvada.

How It Works

Pharmacodynamics: Emtricitabine is a synthetic nucleoside analog of cytidine. After intracellular phosphorylation to emtricitabine triphosphate, it competes with the natural substrate, deoxycytidine triphosphate, and incorporates into viral DNA. This incorporation results in chain termination, effectively blocking the action of the HIV-1 reverse transcriptase enzyme.

Pharmacokinetics:

• Absorption: Emtricitabine is rapidly absorbed after oral administration, with peak plasma concentrations occurring within 1 to 2 hours. Bioavailability is approximately 93%. Food does not significantly affect absorption.

• Distribution: Emtricitabine is widely distributed throughout the body, including the central nervous system.

• Metabolism: Emtricitabine is minimally metabolized by the liver.

• Elimination: Primarily eliminated by the kidneys via glomerular filtration and active tubular secretion, with a terminal half-life of about 10 hours.

Dosage

Standard Dosage

Adults:

• HIV Treatment: 200 mg orally once daily. Alternatively, 240 mg of oral solution once daily.

• PrEP: 200 mg orally once daily, in combination with tenofovir disoproxil fumarate (Truvada or generic).

Children:

• HIV treatment (over 3 months and greater than 33kg): 200mg once a day. Children under 3 months or under 33kg dosage is determined by the doctor, at approximately 6mg/kg.
• PrEP: Use and dose for children weighing less than 35 kg must be determined by a doctor.

Special Cases:

• Elderly Patients: No specific dosage adjustments based on age are generally recommended, but close monitoring for renal function is advised.

• Patients with Renal Impairment: Dose adjustments are needed based on creatinine clearance (CrCl).

  • HIV Treatment: CrCl 30-49 mL/min: 200 mg every 48 hours, CrCl 15-29 mL/min: 200mg every 72 hours, CrCl <15 mL/min: 200mg every 96 hours. Not recommended for CrCl <30 mL/min.
  • PrEP: Not recommended for CrCl <60 mL/min.

• Patients with Hepatic Dysfunction: No dosage adjustment is generally necessary.

• Patients with Comorbid Conditions: Careful consideration is necessary for concomitant medications and their potential for drug interactions (See Drug Interactions)

Clinical Use Cases

Emtricitabine is not typically indicated for use in situations like intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations outside of its core role in HIV treatment or PrEP. Its use in these settings would be primarily related to ongoing HIV management in affected individuals.

Side Effects

Common Side Effects:

Headache, diarrhea, nausea, fatigue, dizziness, skin discoloration, insomnia, abnormal dreams, rash, abdominal pain, cough, rhinitis.

Rare but Serious Side Effects:

Lactic acidosis, severe hepatomegaly with steatosis, immune reconstitution inflammatory syndrome, new or worsening renal impairment, decreased bone mineral density.

Contraindications

Hypersensitivity to emtricitabine. Coadministration with lamivudine. Use for PrEP in individuals with known or suspected HIV infection. Renal impairment below specific CrCl levels (see Dosage).

Drug Interactions

Emtricitabine has minimal drug interactions due to its limited metabolism. However, some clinically significant drug interactions have been noted with other antiretrovirals that are often used in combination regimens. Consult a drug interaction checker for detailed interaction information based on the specific drugs involved, particularly those with renal excretion pathways or known nephrotoxic effects. Consider using a reliable resource to check for potential interactions between emtricitabine and other medications a patient may be taking.

Pregnancy and Breastfeeding

• Pregnancy: Emtricitabine is classified as Pregnancy Category B by the FDA. While animal studies did not demonstrate fetal harm, there are no adequate and well-controlled studies in pregnant women. Emtricitabine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

• Breastfeeding: Emtricitabine is present in human breast milk. The WHO recommends against breastfeeding during emtricitabine treatment. Consider providing formula to infants if the mother is HIV positive.

Drug Profile Summary

• Mechanism of Action: Nucleoside reverse transcriptase inhibitor (NRTI). Inhibits HIV reverse transcriptase, resulting in DNA chain termination.

• Side Effects: Common: headache, diarrhea, nausea, fatigue. Serious: Lactic acidosis, hepatotoxicity, renal impairment.

• Contraindications: Hypersensitivity, concurrent lamivudine, PrEP use in HIV-positive individuals, severe renal impairment.

• Drug Interactions: Limited drug interactions, but consider potential for additive renal toxicity with nephrotoxic agents and other antiretrovirals.

• Pregnancy & Breastfeeding: Category B; Not recommended during breastfeeding.

• Dosage: 200 mg orally once daily (or 240mg oral solution) for HIV treatment and PrEP in combination with tenofovir disoproxil fumarate. Renal dose adjustments necessary.

• Monitoring Parameters: Renal function (CrCl, serum phosphorus, urine glucose, urine protein), liver function tests, HIV viral load, CD4 cell count.

Popular Combinations

Emtricitabine is most commonly used in fixed-dose combinations with tenofovir disoproxil fumarate (Truvada) or tenofovir alafenamide (Descovy) for both HIV treatment and PrEP. These combinations offer the convenience of once-daily dosing and improved adherence. Other combination products include Atripla, Biktarvy, Complera, Genvoya, Odefsey, Stribild, and Symtuza.

Precautions

• General Precautions: Assess renal function prior to and during treatment. Screen for HBV infection before initiating therapy. Monitor for signs of lactic acidosis and hepatotoxicity.

• Specific Populations: (addressed in previous sections)

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Emtricitabine?

A: For HIV treatment and PrEP in adults and adolescents weighing at least 35 kg: 200 mg orally once daily or 240 mg oral solution once daily. Pediatric and renal dosing adjustments are required (See Dosage section).

Q2: How does emtricitabine differ from other NRTIs?

A: Emtricitabine has a long intracellular half-life, allowing for once-daily dosing. It is generally well-tolerated and has a low incidence of side effects compared to some other NRTIs.

Q3: Can emtricitabine be used alone to treat HIV?

A: No, emtricitabine should always be used in combination with other antiretroviral medications for HIV treatment. Monotherapy can lead to the development of drug resistance.

Q4: What are the key patient counseling points for emtricitabine?

A: Emphasize adherence to the prescribed regimen. Advise patients to report any new or worsening symptoms, especially those suggestive of lactic acidosis, hepatotoxicity, or renal problems. Discuss safe sex practices, even when using PrEP, as it doesn’t offer 100% protection against HIV.

Q5: How is emtricitabine used for PrEP?

A: Emtricitabine is used in combination with tenofovir disoproxil fumarate (Truvada) as PrEP. It is taken once daily to reduce the risk of HIV acquisition in high-risk individuals. Regular HIV testing and renal function monitoring are essential for those on PrEP.

Q6: What should be done if a patient on emtricitabine develops renal impairment?

A: Renal function should be closely monitored. Dose adjustment or discontinuation may be necessary depending on the severity of the impairment and the specific drug regimen.

Q7: Can emtricitabine cure Hepatitis B?

A: No, emtricitabine is not a cure for hepatitis B. While it may suppress HBV replication in some co-infected individuals, it does not eliminate the virus, and discontinuation can lead to exacerbation of hepatitis B.

Q8: Are there any specific dietary restrictions with emtricitabine?

A: No specific dietary restrictions are associated with emtricitabine. It can be taken with or without food.

Q9: What are the signs of lactic acidosis that patients should be aware of?

A: Patients should be instructed to report any symptoms such as muscle pain or weakness, numbness or coldness in the extremities, trouble breathing, stomach pain, nausea with vomiting, rapid or uneven heart rate, dizziness, or feeling very weak or tired.

Q10: What is the role of emtricitabine in fixed-dose combination therapy for HIV?

A: Emtricitabine’s inclusion in several fixed-dose combination tablets simplifies treatment regimens, improving adherence and reducing pill burden. The specific combinations allow for tailoring therapy to individual patient needs and resistance profiles.