There were no clinically significant pharmacokinetic interactions when tenofovir disoproxil fumarate was coadministered with rifampicin.

Coadministration of rifampicin-based TB treatment (rifampicin 450 mg in patients <50 kg or 600 mg in patients >50 kg, once daily; with isoniazid, pyrazinamide and ethambutol) and efavirenz/tenofovir-DF/emtricitabine (600/245/200 mg, once daily) was studied in 21 TB-HIV coinfected patients in a crossover study. Coadministration increased efavirenz AUC, Cmax and Cmin by 8%, 2% and 11%, respectively; tenofovir AUC and Cmin increased by 13% and 9% respectively, while Cmax decreased by 2%; emtricitabine AUC and Cmin increased by 5% and 26% respectively, while Cmax decreased by 3%. Bioequivalence for the TB drugs was suggested for Cmax when administered with and without efavirenz/tenofovir/emtricitabine (coadministration decreased rifampicin by 14%, decreased isoniazid by 5%, increased pyrazinamide by 14% and had no effect on ethambutol). The combination was tolerated well by Tanzanian TB–HIV-coinfected patients. The authors conclude that coadministration of the standard first-line TB treatment regimen with efavirenz, tenofovir and emtricitabine does not alter pharmacokinetic parameters.

The pharmacokinetic interaction of rifampicin (600 mg once daily) and tenofovir-DF (300 mg once daily) was assessed in 23 HIV-negative subjects. Coadministration of rifampicin reduced tenofovir AUC by 12%, Cmax by 16% and Cmin by 15%. However, 90% confidence intervals for these PK parameters were within the limits required for pharmacokinetic equivalence. Rifampicin pharmacokinetic parameters were comparable to historical controls. The addition of rifampicin to tenofovir-DF was well tolerated and the small decrease in tenofovir exposure suggests that these drugs can be coadministered without the need for dose adjustments.