No significant effect on tenofovir and etravirine PK parameters is seen. Coadministration with tenofovir-DF (300 mg once daily) increased tenofovir AUC (15%), Cmax (15%) and Cmin (19%). Etravirine AUC and Cmax decreased by 19% and Cmin decreased by 18%. Etravirine and tenofovir can be used without dose adjustments.
Intelence Summary of Product Characteristics, Janssen-Cilag Ltd, March 2019.

The interaction between etravirine and tenofovir-DF was evaluated in clinical studies and no dose adjustment is needed for either drug. Coadministration of tenofovir-DF (300 mg once daily) and etravirine was studied in 23 subjects. Etravirine Cmax and AUC decreased by 19%, and Cmin decreased by 18%. Data from 19 subjects showed that tenofovir Cmax and AUC increased by 15% and Cmin increased by 19%.
Intelence US Prescribing Information, Janssen Therapeutics, July 2019.

Plasma concentrations of etravirine were determined at weeks 4 and 24 in a pharmacokinetic substudy of both DUET trials, and the effect of concomitant tenofovir-DF on etravirine AUC or trough concentration assessed. Data were available from 25 HIV+ subjects at week 4 and 23 HIV+ subjects at week 28. Tenofovir decreased etravirine AUC by 26%.
Pharmacokinetics of etravirine are not affected by sex, age, race, use of enfuvirtide or treatment duration in HIV-1 infected patients. Kakuda TN, Scholler-Gyure M, Peeters M, et al. 9th International Workshop on Clinical Pharmacology of HIV Therapy, New Orleans, April 2008, abstract P34.

Coadministration of tenofovir (300 mg once daily) and etravirine (200 mg twice daily) was studied in 24 HIV- subjects. When combined with tenofovir-DF, etravirine AUC and Cmax both decreased by 19%, and Cmin decreased by 18%. Tenofovir AUC and Cmax both increased by 15%, and Cmin increased by 19%. The changes were not considered to be clinically relevant and the drugs can be co-administered without dose modifications.
Scholler-Gyure M, Debroye C, Woodfall B, et al. Pharmacokinetic evaluation of the interaction between TMC125 and tenofovir disoproxil fumarate. 46th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco. September 2006, abstract A-371.