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As with other calcium-channel blockers, amlodipine may enhance the antihypertensive effects of other drugs for hypertension. Combination with β-blockers, however, is said to be well tolerated.
Concomitant use of Amlokard with aldesleukin and antipsychotics that cause hypotension may enhance its antihypertensive effect. Amlodipine also show additive effect when used with diuretics, β-blockers and angiotensin-converting enzyme inhibitors.
In hypertensive patients with diabetes, the use of amlodipine 5 mg/day with quinapril 20 mg/day was found to be more effective in lowering blood pressure than with quinapril 40 g/day alone.
Amlodipine may be used in combination with atorvastatin in the treatment of cardiovascular risk.
Amlodipine, being mainly metabolized in the liver, may cause interaction with other drugs eg, quinidine which has the same metabolic pathway.
The effects of amlodipine may be reduced by rifampicin and enzyme-inducing antiepileptic drugs eg, carbamazepine, phenobarbital and phenytoin. Enzyme inhibitors eg, cimetidine, erythromycin and HIV-protease inhibitors may interfere with the metabolism of amlodipine and other calcium-channel blockers.
In general, the bioavailability of orally administered calcium-channel blockers is significantly increased when taken with grapefruit juice. However, in a study done in 20 normal men, co-administration of grapefruit juice with amlodipine did not change the pharmacokinetic and pharmacodynamic properties of Amlokard. Therefore, in clinical practice, no significant change is expected to be seen in the profile of response of patients taking amlodipine with grapefruit juice.
