Felodipine (FDP)

Felodipine is a calcium channel blocker (calcium antagonist), a drug used to control hypertension (high blood pressure). Studies dating back to 1989 have suggested that felodipine in combination with grapefruit juice can cause toxic effects. Contraindicated with allergy to felodipine or other calcium channel blockers, sick sinus syndrome, heart block (second and third degree), lactation. Use cautiously with pregnancy, impaired hepatic function.

Oral administration of felodipine is first metabolized in the gastrointestinal tract and liver by the enzyme CYP3A4. Grapefruit juice contains bergamottin which is found to have an inhibiting effect over this enzyme and as a result the bioavailability of the drug increases, raising the risk for abnormal side effects.