Pharmacokinetics of diltiazem and other calcium entry blockers

Diltiazem, as well as other calcium entry blockers, is widely prescribed for the treatment of various types of angina. This review summarizes the current state of knowledge of the pharmacokinetics of diltiazem and of two other calcium entry blockers: verapamil and nifedipine. Although unrelated in their chemical structure, these three drugs have common features. They are highly lipophilic and have a large volume of distribution, are mainly cleared by metabolism and undergo an extensive first-pass extraction. On the other hand, as expected from their quite dissimilar structures, they have their own particular kinetic characteristics. For example, metabolism of diltiazem and verapamil gives rise to active metabolites; repeated administration influences the kinetic profile of verapamil but not those of diltiazem and nifedipine. Absorption, distribution and elimination of these three drugs are differently affected by age and pathological conditions. The possible drug interactions involving diltiazem and the other calcium entry blockers are discussed, particularly that with digoxin. Due to its large therapeutic index, there is no need for treatment monitoring of diltiazem. Nevertheless, this procedure may provide useful information for optimizing the dosage regimen of each patient as the pathological condition and drug therapy may be quite complex.