Clinical pharmacology of calcium antagonists.

The pharmacokinetics of the different calcium antagonists has many similarities and is characterized by incomplete bioavailability due to first-pass metabolism, predominant hepatic biotransformation with negligible amounts of unchanged renal excretion, and a high protein binding. Several of the newer dihydropyridine derivatives have prolonged half-lives allowing once-daily administration. Pharmacological effects usually depend on serum drug concentrations, but the presence of stereoisomers and active metabolites may influence the concentration-effect relationships. In patients with liver disease, the clearance of some calcium antagonists is markedly decreased, whereas in renal failure the elimination rate is not reduced. Calcium antagonists also participate in various drug interactions, in particular with digoxin.