Pharmacokinetic Assessment of Atazanavir and Favipiravir Following Echinacea Supplementation: A Controlled Herb-Drug Interaction Investigation.

Echinacea is a widely used herbal supplement and is frequently co-administered with antiviral drugs, raising concerns regarding potential herb-drug interactions. This study evaluated the effect of repeated Echinacea administration on the pharmacokinetics of favipiravir and atazanavir in rats. Male Sprague Dawley rats were administered Echinacea (250 mg/kg) or vehicle once daily for 10 days, followed by a single oral dose of favipiravir (70 mg/kg) or atazanavir (35 mg/kg). Plasma drug concentrations were quantified using validated LC-MS/MS methods, and pharmacokinetic parameters were determined by noncompartmental analysis. Echinacea co-administration did not significantly alter favipiravir exposure (Cmax: 39,677 ± 5385 vs. 36,364 ± 5379 ng/mL; AUC0-t: 144,457 ± 17,267 vs. 104,840 ± 27,001 ng h/mL) or atazanavir exposure (Cmax: 3274 ± 256 vs. 4004 ± 629 ng/mL; AUC0-t: 8962 ± 1667 vs. 10,645 ± 2949 ng h/mL). No relevant changes were observed in clearance, half-life, or mean residence time for either drug. These findings indicate that repeated Echinacea administration does not result in a pharmacokinetically relevant interaction with favipiravir or atazanavir under the investigated conditions.