Liverpool HIV Interactions

No Interaction Expected

Efavirenz (EFV)

Emtricitabine (FTC)

Quality of Evidence: Very Low

Summary:

Based on the results of in vitro experiments and the known elimination pathways of emtricitabine, the potential for CYP450 mediated interactions involving emtricitabine with other medicinal products is low. The coadministration of emtricitabine, didanosine and efavirenz was studied in 9 treatment naive, HIV+ patients. When compared to historical data for each drug alone, the pharmacokinetics of emtricitabine were not affected, didanosine AUC and Cmax were higher than expected and efavirenz Cmax, Cmin and AUC were lower than expected. However, efavirenz concentrations may have been underestimated as dosing was delayed by 12 hours for ease of sampling.

Description:

In vitro, emtricitabine did not inhibit metabolism mediated by any of the following human CYP450 isoforms: 1A2, 2A6, 2B6, 2C9, 2C19, 2D6 and 3A4. Emtricitabine did not inhibit the enzyme responsible for glucuronidation. Based on the results of these in vitro experiments and the known elimination pathways of emtricitabine, the potential for CYP450 mediated interactions involving emtricitabine with other medicinal products is low.

Emtriva Summary of Product Characteristics, Gilead Sciences International Ltd, July 2011.

At concentrations up to 14-fold higher than those observed in vivo, emtricitabine did not inhibit in vitro drug metabolism mediated by any of the following human CYP450 isoforms: CYP1A2, CYP2A6, CYP2B6, CYP 2C9, CYP2C19, CYP2D6 and CYP3A4. Emtricitabine did not inhibit the enzyme responsible for glucuronidation (uridine-5'-disphosphoglucuronyl transferase). Based on the results of these in vitro experiments and the known elimination pathways of emtricitabine, the potential for CYP450 mediated interactions involving emtricitabine with other medicinal products is low.

Emtriva Presrcibing Information, Gilead Sciences Inc, November 2011.

Specific interaction studies have not been performed with efavirenz and NRTIs other than lamivudine, zidovudine, and tenofovir disoproxil fumarate. Clinically significant interactions are not expected since the NRTIs are metabolised via a different route than efavirenz and would be unlikely to compete for the same metabolic enzymes and elimination pathways. No dosage adjustment is necessary for either medicinal product.

Sustiva Summary of Product Characteristics, Bristol-Myers Squibb Pharmaceuticals Ltd, May 2023.

No dosage adjustment is recommended when efavirenz is given with emtricitabine.

Efavirenz US Prescribing Information, Aurobindo Pharma Limited, October 2021.

Emtricitabine + Didanosine
The coadministration of emtricitabine (200 mg once daily), didanosine (400 mg once daily for patients 60 kg and over; 250 mg once a daily for patients less than 60 kg) and efavirenz (600 mg once daily) was studied in 9 treatment naive, HIV+ patients. When compared to historical data for each drug alone, the pharmacokinetics of emtricitabine were not affected, didanosine AUC and Cmax were higher than expected and efavirenz Cmax, Cmin and AUC were lower than expected. The authors suggest the efavirenz concentrations may have been underestimated as they delayed dosing by 12 hours for ease of sampling.

Pharmacokinetics of emtricitabine, didanosine and efavirenz administered once-daily for the treatment of HIV-infected adults (pharmacokinetic substudy of the ANRS trial). Molina J-M, Peytavin G, Perusat S et al. HIV Medicine, 2004, 5: 99-104.

View all available interactions with Efavirenz (EFV) by clicking here.