Interaction of citrus juices with felodipine and nifedipine Six men with borderline hypertension took felodipine 5 mg with water, grapefruit juice, or orange juice. The mean felodipine bioavailability with grapefruit juice was 284 (range 164-469)% of that with water. The dehydrofelodipine/felodipine AUC ratio was lower, diastolic blood pressure lower, and heart rate higher with grapefruit juice than with water. Vasodilatation-related side-effects were more frequent. Orange juice had no such effects. Six healthy men took nifedipine 10 mg with water or grapefruit juice; the bioavailability with grapefruit juice was 134 (108-169)% of that with water. 