Emtricitabine is not an inhibitor of human CYP 450 enzymes. Nevirapine and emtricitabine may be coadministered without dose adjustments. Tenofovir plasma levels remain unchanged when co-administered with nevirapine. Nevirapine plasma levels were not altered by co-administration of tenofovir-DF. Tenofovir-DF and nevirapine can be co-administered without dose adjustments.

The effect of tenofovir-DF/emtricitabine on the pharmacokinetics of nevirapine (200 mg twice daily) was studied in 7 HIV+, African-American subjects. The mean ± sd steady state nevirapine Cmin was 4971 ± 1985 ng/ml and was comparable to historical values. The mean nevirapine Cmin after the 200 mg once daily 2 week lead-in phase was also determined and was 2876 ng/ml. 

The interaction between tenofovir-DF and nevirapine was assessed in TDM samples from groups of HIV+ patients receiving nevirapine (200 mg twice daily or 400 mg once daily) alone or with tenofovir-DF (300 mg once daily). For twice daily dosing, although nevirapine samples were collected at various times post dose (0.2-14.3 h), there was no significant difference in the times post dose between the control group (n=272) and the tenofovir group (n=39). Nevirapine concentrations were not significantly different between the groups (5.68 µg/ml vs. 6.48 µg/ml, control vs. tenofovir). For once daily dosing, samples were collected 0-24.4 h post dose in the control group (n=18) and the tenofovir group (n=94). There was no significant difference between the groups for the time post dose or nevirapine concentrations (5.25 µg/ml vs. 4.85 µg/ml, control vs. plus tenofovir). 

Trough nevirapine concentrations (23-25 h post dose) were obtained from patients undergoing routine TDM whilst receiving nevirapine (400 mg once daily). Geometric mean (CI) nevirapine troughs in 171 patients receiving nevirapine and tenofovir-DF were 3420 (3170-3670) ng/ml. Values for patients receiving nevirapine without tenofovir (n=87) were 3260 (2980-3540) ng/ml, suggesting that tenofovir does not affect nevirapine plasma concentrations.