The pharmacokinetics of angiotensin converting enzyme inhibitors in patients with renal impairment.

The clearance of drugs excreted entirely unchanged by the kidneys is assumed to relate directly to renal function. The clearance of drugs which are entirely metabolized is usually not altered in patients with renal impairment, although there are examples of both increased and decreased metabolic clearance rates. The clearance of metabolites which are excreted unchanged through the kidneys is also directly related to renal function. The angiotensin converting enzyme (ACE) inhibitors enalapril, ramipril, cilazapril and quinapril are prodrugs that are rapidly converted to active metabolites which are excreted unchanged through the kidneys. Studies have consistently demonstrated reduction in the apparent oral clearance of the active metabolites, in proportion to the degree of impairment of renal function. In addition, for quinapril at least, the metabolic clearance of the parent drug is slightly reduced in renal impairment. The activity of captopril and lisinopril lies in the parent molecule itself. Lisinopril is excreted renally unchanged, while captopril is both metabolized and excreted renally unchanged. The duration of ACE inhibition after administration of any of the ACE inhibitors is prolonged in proportion to the degree of renal impairment. From these pharmacokinetic and pharmacodynamic properties, it follows that the dose rate of the ACE inhibitors should be reduced in direct proportion to the degree of reduction in renal function. Reducing the dose, rather than prolonging the dose interval, is more logical for compliance and for maintaining a consistent degree of ACE inhibition over 24 h.