Emtricitabine Uses
Emtricitabine is a nucleoside reverse transcriptase inhibitor used in combination with other antiretroviral agents for the treatment of HIV-1 infection in adults and children, and as part of pre-exposure prophylaxis (PrEP) regimens to prevent HIV acquisition in high-risk populations. 1
HIV-1 Treatment
Initial Therapy in Treatment-Naïve Patients
Emtricitabine combined with tenofovir disoproxil fumarate (TDF) plus an integrase strand transfer inhibitor (InSTI) represents a recommended optimal initial regimen for most patients with HIV-1 infection. 2
Emtricitabine/TDF can also be combined with non-nucleoside reverse transcriptase inhibitors (NNRTIs) or boosted protease inhibitors as effective alternative regimens. 2
The combination of efavirenz/TDF/emtricitabine demonstrates high efficacy particularly in patients with baseline HIV RNA levels >100,000 copies/mL, though efavirenz carries risks of neuropsychiatric adverse effects and increased suicidality. 2
Rilpivirine/TDF (or TAF)/emtricitabine offers the lowest risk of rash among NNRTI-based therapies but is not recommended for patients with HIV RNA >100,000 copies/mL or CD4 count <200/μL due to increased virologic failure risk. 2
Treatment-Experienced Patients
Emtricitabine-based regimens are effective in treatment-experienced patients when combined with boosted protease inhibitors, maintaining durable viral suppression. 3
The use of emtricitabine in treatment-experienced patients should be guided by genotypic or phenotypic resistance testing to ensure viral susceptibility. 4
Pediatric Use
Emtricitabine is approved for use in children and adolescents (aged 13 months to 17 years in clinical trials), with dosing calculated based on body weight. 1, 5
Triple therapy including emtricitabine 6 mg/kg once daily achieved or maintained HIV RNA suppression to <400 copies/mL in approximately 90% of pediatric patients after 16-24 weeks. 4
HIV Pre-Exposure Prophylaxis (PrEP)
Daily PrEP Regimens
Daily oral TDF/emtricitabine is the recommended PrEP regimen for all populations at risk of HIV through sexual exposure or injection drug use. 6
PrEP is recommended for populations with annual HIV incidence of at least 2% and for HIV-seronegative partners of HIV-infected persons who are not consistently virally suppressed. 2, 7
Daily dosing is especially critical for women, as tenofovir concentrates at 10-fold lower levels in vaginal tissue compared to rectal tissue, with faster clearance. 6, 7
On-Demand (Event-Driven) PrEP
On-demand TDF/emtricitabine using 2-1-1 dosing (2 doses 2-24 hours before sex, 1 dose 24 hours later, 1 dose 24 hours after that) is effective for HIV prevention in men who have sex with men, demonstrating 86% risk reduction. 6
On-demand PrEP is only recommended for cisgender men and transgender women having planned receptive anal sex—it is not validated for receptive vaginal exposures or people who inject drugs. 2, 6
On-demand dosing has only been validated with TDF/FTC, not with TAF/FTC. 6
Time to Protection
For receptive vaginal sex, 7 days of daily TDF/emtricitabine dosing is required to achieve full protection. 6
For receptive anal sex, protection can be achieved more rapidly within 2-3 days with adequate dosing. 6
A 1-week lead-in time is recommended with daily dosing for rectal, penile, and vaginal exposures to ensure adequate tissue levels. 2
PrEP Discontinuation
- At PrEP discontinuation, TDF/emtricitabine should continue for 1 week after the last sexual exposure to maintain protection during the washout period. 2, 6
Hepatitis B Virus (HBV) Co-infection
Treatment Considerations
Emtricitabine demonstrates potent activity against hepatitis B virus in patients co-infected with HIV-1 and HBV, as well as in HBV monoinfection. 8, 5
All patients must be tested for HBV infection (HBsAg) before starting emtricitabine, as severe acute exacerbations of hepatitis B can occur upon discontinuation in co-infected patients. 1
Critical Safety Warning
For individuals with active HBV infection (detectable HBsAg), discontinuation of TDF/emtricitabine PrEP could lead to acute HBV flares or hepatic decompensation, particularly in patients with hepatic cirrhosis. 2
Careful monitoring of HBV infection and liver function is mandatory for several months after stopping emtricitabine in HBV-infected patients. 1
On-demand PrEP is contraindicated in patients with active HBV infection due to the risk of hepatitis flare and hepatic decompensation. 2
Dosing and Administration
Standard Dosing
The recommended dose of emtricitabine for HIV treatment is one 200 mg capsule once daily, with or without food. 1, 8
For PrEP, the standard dose is one tablet daily containing TDF 300 mg/emtricitabine 200 mg. 9
Emtricitabine has a favorable pharmacokinetic profile permitting once-daily dosing, with a plasma elimination half-life of 8-10 hours and intracellular triphosphate half-life of 39 hours. 5
Renal Considerations
TDF-based PrEP is not recommended in persons with creatinine clearance below 60 mL/min/1.73m². 2
Measurement of serum creatinine and estimated glomerular filtration rate is recommended before PrEP initiation and at least every 6 months during treatment. 2
Monitoring Requirements
HIV Treatment Monitoring
HIV RNA level should be measured within the first 6 weeks of starting emtricitabine-based therapy, then every 3 months until <50 copies/mL for 1 year, then every 6 months. 2
CD4 cell count should be monitored every 6 months until >250/μL for 1 year, then can be discontinued as long as virus is suppressed. 2
PrEP Monitoring
HIV testing with a combination antigen-antibody assay is mandatory before initiating PrEP and every 3 months during treatment. 2, 6
PrEP prescriptions should not exceed 90 days without interval HIV testing. 2, 7
STI screening (gonorrhea, chlamydia, syphilis) should be performed quarterly during PrEP. 2, 7
HCV serologic testing should be performed at least annually and more frequently in high-risk individuals. 2
Pregnancy testing is recommended at each visit for individuals of childbearing potential. 7
Common Pitfalls and Caveats
Never use emtricitabine as monotherapy—it must always be combined with other antiretroviral agents to prevent resistance development. 1
Viral strains resistant to emtricitabine are cross-resistant to lamivudine and vice versa. 10
Daily TAF/emtricitabine for PrEP should be limited to cisgender men and others whose exposures do not include receptive vaginal sex or injection drug use alone, as it lacks validation for these populations. 6
Emtricitabine does not prevent other sexually transmitted infections—only HIV. 7
Missing doses of emtricitabine lowers blood levels and increases risk of treatment failure or HIV acquisition. 1
Patients should not discontinue emtricitabine without first consulting their healthcare provider, particularly those with HBV co-infection. 1