Calcium antagonists block calcium entry into cells, resulting in relaxation of smooth muscle and limitation of the cytotoxic effects of ischaemia in various organ systems. They are most frequently used for clinical conditions requiring vasodilatation, i.e. hypertension and Raynaud's phenomenon, and this also suggests that the most common adverse effect of these drugs for noncardiovascular indications is an unwanted decline in blood pressure.
Other uses include treatment of supraventricular arrhythmias and angina. There is some evidence that these drugs retard the development of atherosclerosis. Calcium channel blockers also improve renal reperfusion and may reduce renal insufficiency due to various nephrotoxins, and are particularly useful in renal transplantation for protection against cyclosporin toxicity and post-transplant acute tubular necrosis. These drugs are also useful in pregnancy-induced hypertension and unwanted uterine contraction. Affective disorders and malignancies may be other conditions which benefit from calcium antagonist therapy.
Calcium antagonists, in particular nimodipine which is most selective for the cerebral vasculature, have been approved for treating vasospasm after subarachnoid haemorrhage. They are probably also effective for treatment of migraine. Calcium channel blockers may be effective for treating acute cerebral infarction, but results of clinical trials to date have been equivocal, largely because it has been difficult to recruit patients within the short interval after the onset of stroke when these drugs would be most effective, and because of the unwanted hypotensive effect of high doses.