To determine the influence of Echinacea purpurea on the pharmacokinetics of lopinavir-ritonavir, and on CYP3A and P-glycoprotein (P-gp) activity using the probe substrates midazolam, and fexofenadine, respectively.
Open label, single-sequence pharmacokinetic study.
Outpatient clinic in a Federal Government research hospital.
Thirteen (8 males) healthy volunteers (median age: 31 yrs).
Measurements and main results
Healthy volunteers received lopinavir-ritonavir (400/100 mg) twice daily for 30 days. On study day 16, subjects began taking Echinacea purpurea 500 mg three times daily, which they continued for four weeks, the first two weeks in combination with lopinavir-ritonavir. On days 15 and 30 of lopinavir-ritonavir administration (pre and post-Echinacea, respectively), serial blood samples were collected over 12 hrs to determine lopinavir and ritonavir concentrations and subsequent pharmacokinetic parameters using non-compartmental methods. Study subjects also received single doses of midazolam (8 mg orally) and fexofenadine (120 mg orally) before- and after 28 days of Echinacea purpurea to assess CYP3A and P-glycoprotein (P-gp) activity, respectively. Neither lopinavir nor ritonavir pharmacokinetics were significantly altered by 2 weeks of Echinacea coadministration. The geometric mean ratios (GMR, 90% CI) for lopinavir area under the concentration vs. time curve from zero to 12 hrs (AUC0–12) and maximum concentration (post-Echinacea/pre-Echinacea) were 0.96 (0.83, 1.10) and 1.00 (0.88, 1.12), respectively (P > 0.05). Conversely, GMRs (90% CIs) for midazolam AUC from time zero to infinity (AUC0-∞) and oral clearance were 0.73 (0.61, 0.85) (P = 0.008) and 1.37 (1.10, 1.63) (P = 0.02), respectively. Fexofenadine pharmacokinetics did not significantly differ pre- and post-echinacea administration (P > 0.05).
Echinacea purpurea induced CYP3A activity but did not alter lopinavir concentrations, most likely due to the presence of the potent CYP3A inhibitor, ritonavir. Echinacea purpurea is unlikely to alter the pharmacokinetics of ritonavir-boosted protease inhibitors but may cause modest decreases in plasma concentrations of other CYP3A substrates.