INTERACTIONS OF GRAPEFRUIT WITH MEDICATIONS
Grapefruit Juice and Calcium Channel Blockers
Several studies recorded the effect of grapefruit juice on calcium channel blockers. The grapefruit juice seems to affect mainly the dihydropyridine family of calcium-channel blockers. Most studies used healthy persons. It is expected that people with existing hypertension or cardiac condition may be more adversely affected by the grapefruit juice interaction.
The following is a summary of clinical findings on how grapefruit juice affects the bio-availability and side reactions of calcium channel blockers.
Felodipine (Plendil, Renedil)
Felodipine was given with double-strength grapefruit juice to six hypertensive patients.
Nifedipine (Adalat, Procardia)
Patients taking nifedipine experienced an increase in AUC by 34%.
In 12 healthy subjects amlodipine AUC was increased by 16% and patients experienced a slight reduction in diastolic blood pressure when amlodipine was given with single-strength grapefruit juice.
In nine patients, nitrendipine AUC was increased by 106% when given with grapefruit juice.
In 12 patients, nisoldipine AUC was increased by 98% when given with grapefruit juice, and peak concentrations were increased by 406%. There was marked variation within individuals as to how they reacted to the grapefruit juice. Only minor effects on blood pressure and heart rate were noted.
Verapamil (Isoptin, Calan)
In a crossover study of 24 volunteers, verapamil and norverapamil AUCs were increased 43% and 28%, while the maximum plasma concentration of verapamil and norverapamil were increased 60% and 32%. Four subjects in the grapefruit juice-verapamil phase had a PR interval prolongation to greater than 0.24 seconds.
Diltiazem (Cardizem, Tiazac)
Nine healthy male subjects received 120mg diltiazem with either 200 mL of water or single-strength grapefruit juice.
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