INTERACTIONS OF GRAPEFRUIT WITH MEDICATIONS

Lovastatin (Mevacor)

Kantola T et al. ( Clin Pharmacol Ther 1998; 63: 397-402) studied ten healthy subjects in an open randomized crossover trial to determine how grapefruit juice interacts with lovastatin. The subjects drank 200 mL double strength grapefruit juice or water for two days before being given a single 80 mg dose of lovastatin ( 2-4 times the usual dosage).

The authors advised that co-administration of lovastatin with grapefruit juice be avoided.

To keep these results in perspective, the study employed double strength grapefruit juice and higher than normal dosage of lovastatin. However, a 15-fold increase in AUC and a 12-fold increase in peak levels as a result of interaction with grapefruit juice should be of serious concern. 

A group of researchers from Merck (the manufacturer of Mevacor) conducted their own research to determine the effect of grapefruit juice on normal dosage of lovastatin. Sixteen healthy subjects received either 8 ounces of single-strength GJ or water with breakfast for 3 consecutive days. The subjects then received a single 40mg dose of lovastatin in the evening of the third day. The AUC and Cmax of all active HMG-CoA reductase inhibitors increased by approximately 40% each in the GJ group. The AUC and Cmax values for lovastatin approximately doubled in the GJ patients, and lovastatin acid AUC and Cmax increased 1.6 fold. The authors explained the lower interaction in their experiment by the fact that they used a normal dose of lovastatin (40mg daily in the evening) and a normal amount of grapefruit juice (one regular strength glass daily with breakfast). They concluded that daily consumption of a glass of regular-strength GJ has a minimal effect on plasma concentrations of HMG-CoA reductase inhibitors after a 40mg evening dose of lovastatin. 

Simvastatin (Zocor)

Ten healthy volunteers received either 200 mL water or double strength grapefruit juice three times daily for 2 days before receiving a single 60mg dose of simvastatin (Note: 3-6x the usual dosage), in a randomized crossover fashion. Lilja, JJ, Kivisto KT, Neovonen PJ. ( Clin Pharmacol Ther 1998; 64: 477-83), who conducted the clinical trial reported that grapefruit juice increased:

Time to peak concentration of simvastatin was increased from 1 hour to 2.5 hours. 

Again, to keep things in perspective, double-strength grapefruit juice was used, and a higher than usual dose of simvastatin was used in the study. But the grapefruit juice interaction is quite  dramatic on the simvastatin blood levels. The authors recommended that you do not use grapefruit juice and simvastatin simultaneously, or to use substantially lower dosage of simvastatin when used in combination with grapefruit juice. 

Atorvastatin (Lipitor)

Lilja JJ, and co-investigators ( Clin Pharmacol Ther 1999; 66: 118-27) reported the results of clinical trials conducted to determine how grapefruit juice intracts with atorvastatin and provastatin.

Twelve healthy volunteers received either 200 mL water or double strength grapefruit juice three times daily for two days before receiving a single 40 mg dose of atorvastatin with either 200 mL water or grapefruit juice in a randomized crossover fashion. Subjects took an additional 200 mL water or grapefruit juice three times daily on day 4 and 5 as well. 

Grapefruit juice increased:

Atorvastatin has two active metabolites: atorvastatin lactone and 2-hydroxyatorvastatin acid which were also affected by GJ, with the AUC of active and total HMG-CoA reductase inhibitors being increased 1.3 fold and 1.5 fold respectively. 

Grapefruit juice interacts with atorvastatin (lipitor) by a much less extent than its effect on lovastatin and simvastatin. The authors concluded that grapefruit juice, at least in large amounts, should not be used concomitantly with atorvastatin, or the dosage of atorvastatin should be reduced accordingly.

Pravastatin (Pravachol)

Eleven healthy volunteers received either 200 mL water or double strength grapefruit juice three times daily for two days before receiving a single 40mg dose of pravastatin with either 200 mL water or grapefruit juice in a randomized crossover fashion. Grapefruit juice had no significant effects on the pharmacokinetics of pravastatin, other than the tmax of active HMG Co-A reductase inhibitors was significantly prolonged from 1 hour to 2 hours. The authors concluded that pravastatin is not susceptible to interaction with grapefruit juice and other CYP3A4 inhibitors.

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