Drug Interactions between cat's claw and ritonavir

GENERALLY AVOID: A case report suggests that concomitant use of cat's claw may increase the plasma concentrations of protease inhibitors. The exact mechanism of interaction is unknown, although cat's claw has been found in one study to inhibit CYP450 3A4 metabolism in vitro. The case patient was a 45-year-old woman with HIV and hepatitis C coinfection who was scheduled to receive a liver transplantation. Her antiretroviral regimen prior to transplantation consisted of abacavir (600 mg/day), lamivudine (300 mg/day), atazanavir (300 mg/day), ritonavir (100 mg/day), and saquinavir (2000 mg/day). In addition, she was receiving sildenafil and epoprostenol for pulmonary hypertension. When serum protease inhibitor levels were measured before the transplantation, trough levels (Cmin) were 1.22 mcg/mL for atazanavir, 6.13 mcg/mL for ritonavir, and 3.4 mcg/mL for saquinavir. No signs or symptoms of overdosage were observed. Subsequent questioning of the patient revealed that she had been taking a cat's claw preparation for the past two months, which was the only relevant change according to the authors. The patient was instructed to discontinue the herbal product. Two weeks later, Cmin values normalized to 0.3 mcg/mL for atazanavir, 0.92 mcg/mL for ritonavir, and 0.64 mcg/mL for saquinavir. The patient continued on the same antiretroviral regimen thereafter without further incident.

MANAGEMENT: Although data are limited, use of cat's claw preparations should preferably be avoided in patients treated with protease inhibitors. Otherwise, clinicians should consider monitoring serum protease inhibitor levels, especially following initiation or discontinuation of any cat's claw product. Patients should consult a healthcare provider before taking any herbal or alternative medicine.