Increased concentrations of atazanavir, saquinavir and ritonavir were reported in a patient taking Cat’s claw whilst being treated with atazanavir (300 mg once daily), saquinavir (2000 mg once daily), ritonavir (100 mg once daily), abacavir and lamivudine. Trough concentrations of the protease inhibitors were determined and found to be supratherapeutic (atazanavir 1.22 µg/ml; saquinavir 3.4 µg/ml; ritonavir 6.13 µg/ml), though no signs or symptoms of overdosage were observed. Concentrations were evaluated 15 days after stopping Cat’s claw and were found to have normalised (atazanavir 0.3 µg/ml; saquinavir 0.64 µg/ml; ritonavir 0.92 µg/ml). 
Interaction between cat's claw and protease inhibitors atazanavir, ritonavir and saquinavir. Lopez Galera RM, Ribera Pascuet E, Esteban Mur JI, et al. Eur J Clin Pharmacol. 2008, 64(12):1235-6.