No interaction between tipranavir/ritonavir and efavirenz

This study investigated the effect of steady-state efavirenz on steady-state tipranavir/ritonavir pharmacokinetics in 16 HIV negative adult female and male
volunteers.

After dosing with tipranavir/ritonavir (500/200 mg twice daily with food) for 10 days, efavirenz (600 mg once daily) was added to the regimen for 14 days. Intensive pharmacokinetic sampling was done on days 10 and 24. The geometric mean ratios (90% confidence intervals) for AUC, Cmax, and Cmin comparing TPV/r alone and in combination with EFV were 0.97 (0.87 to 1.09), 0.92 (0.81 to 1.03), and 1.19 (0.93 to 1.54) for tipranavir, and 1.03 (0.78 to 1.38), 0.92 (0.65 to 1.30), and 1.04 (0.72 to 1.48) for ritonavir.

With the exception of a 19% increase in tipranavir Cmin, which is considered not to be clinically relevant, efavirenz had no effect on the steady-state pharmacokinetics of tipranavir or ritonavir. Tipranavir/ritonavir can be safely coadministered with efavirenz and without the need for a dose adjustment.

Ref: la Porte CJ et al. Lack of effect of efavirenz on the pharmacokinetics of tipranavir-ritonavir in healthy volunteers. Antimicrob Agents Chemother, 2009, 53(11): 4840-4844.
http://www.ncbi.nlm.nih.gov/pubmed/19721063