Clinical pharmacological aspects of calcium antagonists and their therapeutic role in hypertension.
Calcium antagonists are effective antihypertensive drugs as monotherapy or in combination with other drugs. Unlike beta-blockers and diuretics, there may be a closer correlation between drug levels in plasma and fall in blood pressure, at least in individuals. Pharmacokinetic factors are likely to be more important for this group of drugs. Both nifedipine and verapamil are subject to considerable and variable "first pass" metabolism by the liver resulting in wide interindividual differences in plasma levels. Nifedipine as capsules has a short duration of effect corresponding to its short half-life. Verapamil appears to modify its own clearance and metabolism with a prolongation of half-life after chronic dosing. Verapamil influences the pharmacokinetics of other coadministered drugs such as prazosin with increased plasma levels and a greater blood pressure response. A clearer understanding of the acute and chronic pharmacokinetics will allow the clinician to use calcium antagonists more effectively and safely.