Grapefruit juice enhances the bioavailability of the HIV protease inhibitor saquinavir in man.

AIMS: Saquinavir is a potent HIV protease inhibitor whose effectiveness is limited in vivo by its low bioavailability. Since saquinavir is metabolized by CYP3A4, the effect of grapefruit juice, an inhibitor of CYP3A4, was investigated on its bioavailability. METHODS: After an overnight fast, eight healthy volunteers were treated with either 400 ml grapefruit juice or water before intravenous (12 mg) or oral saquinavir (600 mg) was administered. Serial blood samples were obtained over the following 24 h and standardized meals were served 5 and 10 h after the administration of saquinavir. The plasma concentrations of saquinavir were determined by high-performance liquid chromatography and pharmacokinetic parameters were calculated by routine methods. RESULTS: The AUC was not affected by grapefruit juice after intravenous administration, but it increased significantly from 76+/-96 (water, mean (s.d.) to 114+/-70 (microg l[-1] h) (grapefruit juice) after oral saquinavir. Similarly, the oral bioavailability of saquinavir increased by a factor of 2 with grapefruit juice (from 0.7% to 1.4%). In contrast, clearance, volume of distribution and elimination half-life of saquinavir were not affected by grapefruit juice. After oral, but not after intravenous administration, the plasma concentration-time curve showed a second peak after lunch irrespective of pretreatment, suggesting enhancement of absorption by food. CONCLUSIONS: The studies demonstrate that grapefruit juice increases the bioavailability of saquinavir without affecting its clearance, suggesting that inhibition of intestinal CYP3A4 may contribute. Since the antiretroviral effect of saquinavir is dose-dependent, inhibition of CYP3A4 may represent a way to enhance its effectiveness without increasing the dose.

Interaction between grapefruit juice and midazolam in humans.

OBJECTIVE: To investigate the effects of grapefruit juice on the pharmacokinetics and dynamics of midazolam. METHODS: Eight healthy male subjects participated in this open crossover study. Intravenous (5 mg) or oral (15 mg) midazolam was administered after pretreatment with water or grapefruit juice. We measured the pharmacokinetics and pharmacodynamics (reaction time, Digit Symbol Substitution Test [DSST], general impression judged by the investigators, and drug effect judged by the subjects) of midazolam and the pharmacokinetics of alpha-hydroxymidazolam. RESULTS: In comparison to water, pretreatment with grapefruit juice did not change the pharmacokinetics or pharmacodynamics of intravenous midazolam. After oral administration, pretreatment with grapefruit juice led to a 56% increase in peak plasma concentration (Cmax), a 79% increase in time to reach Cmax (tmax), and a 52% increase in the area under the plasma concentration-time curve (AUC) of midazolam, which was associated with an increase in the bioavailability from 24% +/- 3% (water) to 35% +/- 3% (Grapefruit juice; mean +/- SEM, p < 0.01) After oral administration of midazolam, pretreatment with grapefruit juice was associated with a 105% increase in tmax and with a 30% increase in the AUC of alpha-hydroxymidazolam. For oral midazolam, pretreatment with grapefruit juice led to significant increases in tmax for all dynamic parameters and in the AUC values for the reaction time and DSST, whereas the maximal dynamic effects remained unchanged. CONCLUSIONS: Pretreatment with grapefruit juice is associated with increased bioavailability and changes in the pharmacodynamics of midazolam that may be clinically important, particularly in patients with other causes for increased midazolam bioavailability such as advanced age, cirrhosis of the liver, and administration of other inhibitors of cytochrome P450.