[Principles of the pharmacokinetics and pharmacodynamics of calcium antagonists]

Today calcium antagonists (Ca-antagonists) are widely used agents in the management of various diseases of the circulatory system. More than 20 years ago the Ca-antagonists of the so-called 1st generation (Verapamil, Diltiazem, Nifedipine) were introduced for treatment of angina pectoris and later of essential hypertension. In the last decade an increasing number of agents structurally related to dihydropyridines were developed for the treatment of hypertension and/or coronary heart disease or cerebral disorders; the main target was to reduce side effects and to guarantee once or at least twice daily administration. Therefore the Ca-antagonists of the so-called 2nd generation (e.g. Amlodipine, Felodipine, Isradipine, Nitrendipine, Nicardipine, Nimodipine, Nisoldipine) tend to longer elimination-half-lives; Amlodipin is an exception with an elimination-half-life of 30 hours on the average. Apart from elimination rates, however, the biopharmaceutical and pharmacokinetic characteristics of all Ca-antagonists are similar: they are highly cleared drugs and are relatively highly protein bound. As they are subject to significant hepatic first-pass-metabolism old age and hepatic disease will increase their plasma-concentrations. Renal impairment affects little their pharmacokinetics since the fraction eliminated unchanged by the kidneys is small. For most agents, plasma-concentration-response relationships have been described. With exception of nicardipine a linear pharmacokinetic in all Ca-antagonists was demonstrated. Drugs and food affecting hepatic blood flow and drug metabolising capacity have predictable interaction potential. With regard to the acute pharmacodynamic effects the Ca-antagonists show similar qualitative effects, though there are quantitative differences. Orally administered dihydropyridine-derivatives induce acute hypotensive effects, whereas the other compounds show clinically relevant hypotensive effects only when administered chronically per os or less pronounced when given as intravenous infusion.