Pharmacokinetics of calcium-entry blockers.

Effective use of drugs in therapy depends not only on clinical acumen but also on the availability of relevant pharmacokinetic and pharmacodynamic data. Such information assists in development of safe dosing regimens, prediction of abnormal handling of drugs in states of disease and disorder and anticipation of drug interactions. For the calcium-entry blocking agents now available in the United States (verapamil, nifedipine and diltiazem), these data appeared well after clinical patterns of use evolved. Nonetheless, their relevance continues to be demonstrated by the dependence of each agent on intact liver blood flow and function for normal rates of elimination; by the nonlinear kinetic characteristics for verapamil and diltiazem (and probably for nifedipine, as well) and the derivative implications for decreased dosing frequency requirements; and by observations now appearing on the relation between plasma drug levels and drug effects, both therapeutic and toxic. Such data are discussed herein, with emphasis on those aspects that impact on the clinical use of the calcium-entry antagonists.