STUDY OBJECTIVE:

To determine if milk thistle (silymarin) alters the pharmacokinetics of indinavir.

DESIGN:

Sequential crossover trial.

SETTING:

General clinical research center.

SUBJECTS:

Ten healthy subjects.

INTERVENTION:

Indinavir 800 mg 3 times/day was given for four doses on days 1 and 2. Silymarin 160 mg 3 times/day was given on days 3-15. On day 16 and for one dose on day 17, both drugs were given at the same dosages.

MEASUREMENTS AND MAIN RESULTS:

Indinavir's pharmacokinetic parameters were evaluated at steady state both before and after administration of 14 days of silymarin. Blood samples were collected -0.25, 0.5, 1, 2, 3, 4, and 5 hours after indinavir dosing and assayed by high-performance liquid chromatography. The final pharmacokinetic model had first-order absorption after a lag time, and two compartments with first-order elimination from the central compartment. When given alone and combined with silymarin, respectively, the geometric mean (95% confidence interval [CI]) steady-state indinavir area under the plasma concentration-time curve was 20.7 hr x mg/L (15.3-28.2 hr x mg/L) and 19.4 hr x mg/L (15.8-23.6 hr x mg/L) and the trough plasma concentration was 0.340 mg/L (0.232-0.497 mg/L) and 0.232 mg/L (0.129-0.419 mg/L).

CONCLUSION:

Silymarin has no apparent effect on indinavir plasma concentrations.