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.

Plasma pharmacokinetics of isoniazid were determined in 15 HIV/TB coinfected patients during a study investigating dose increase of rifabutin following commencement of efavirenz. When isoniazid (15 mg/kg twice weekly) was administered with rifabutin (300 mg twice weekly), geometric mean values for isoniazid AUC and Cmax were 29.9 µg/ml.h and 6.8 µg/ml, respectively. After the commencement of efavirenz (600 mg once daily) and an increase in rifabutin to 600 mg twice daily, there was no significant change in isoniazid exposure (AUC 28.6 µg/ml.h, Cmax 7.0 µg/ml).