Pentopril-cimetidine interaction caused by a reduction in hepatic blood flow

Clinical pharmacokinetics and selective pharmacodynamics of new angiotensin converting enzyme inhibitors: an update

The angiotensin converting enzyme (ACE) inhibitors are widely used in the management of essential hypertension, stable chronic heart failure, myocardial infarction (MI) and diabetic nephropathy. There is an increasing number of new agents to add to the nine ACE inhibitors (benazepril, cilazapril, delapril, fosinopril, lisinopril, pentopril, perindopril, quinapril and ramipril) reviewed in this journal in 1990. The pharmacokinetic properties of five newer ACE inhibitors (trandolapril, moexipril, spirapril, temocapril and imidapril) are reviewed in this update. All of these new agents are characterised by having a carboxyl functional groups and requiring hepatic activation to form pharmacologically active metabolites. They achieve peak plasma concentrations at similar times (t(max)) to those of established agents. Three of these agents (trandolapril, moexipril and imidapril) require dosage reductions in patients with renal impairment. Dosage reductions of moexipril and temocapril are recommended for elderly patients, and dosages of moexipril should be lower in patients who are hepatically impaired. Moexipril should be taken 1 hour before meals, whereas other ACE inhibitors can be taken without regard to meals. The pharmacokinetics of warfarin are not altered by concomitant administration with trandolapril or moexipril. Although imidapril and spirapril have no effect on digoxin pharmacokinetics, the area under the concentration-time curve of imidapril and the peak plasma concentration of the active metabolite imidaprilat are decreased when imidapril is given together with digoxin. Although six ACE inhibitors (captopril, enalapril, fosinopril, lisinopril, quinapril and ramipril) have been approved for use in heart failure by the US Food and Drug Administration, an overview of 32 clinical trials of ACE inhibitors in heart failure showed that no significant heterogeneity in mortality was found among enalapril, ramipril, quinapril, captopril, lisinopril, benazepril, perindopril and cilazapril. Initiation of therapy with captopril, ramipril, and trandolapril at least 3 days after an acute MI resulted in all-cause mortality risk reductions of 18 to 27%. Captopril has been shown to have similar morbidity and mortality benefits to those of diuretics and beta-blockers in hypertensive patients. Captopril has been shown to delay the progression of diabetic nephropathy, and enalapril and lisinopril prevent the development of nephropathy in normoalbuminuric patients with diabetes. ACE inhibitors are generally characterised by flat dose-response curves. Lisinopril is the only ACE inhibitor that exhibits a linear dose-response curve. Despite the fact that most ACE inhibitors are recommended for once-daily administration, only fosinopril, ramipril, and trandolapril have trough-to-peak effect ratios in excess of 50%.

Pharmacokinetic drug interactions with anti-ulcer drugs

The safety profile of any pharmacological agent is defined on the basis of its toxicity, tolerability and potential for pharmacokinetic and/or pharmacodynamic interactions with other compounds, which may belong to the same or to a different pharmacological class. Drug-drug interactions are important in clinical practice because short and long term therapeutic regimens frequently require coadministration of different drugs. The pharmacological treatment of gastric and duodenal ulcers (and of related syndromes) includes older and newer compounds, which have different mechanisms of action and exert different therapeutic effects. These compounds are widely prescribed in combination with other drugs being given for the treatment of concomitant diseases. This article reviews pharmacokinetic interactions with anti-ulcer drugs, paying particular attention to those which have clinically relevant adverse effects. Drugs mentioned in the literature as causing any pharmacokinetic interaction with anti-ulcer compounds are considered in this article.

Pharmacokinetic optimisation of angiotensin converting enzyme (ACE) inhibitor therapy

Angiotensin converting enzyme (ACE) inhibitors are increasingly used to treat hypertension and congestive heart failure. Recently, several new ACE inhibitors with pharmacokinetic features different from earlier agents such as captopril or enalapril have come into use. This review discusses the use of pharmacokinetics to optimise ACE inhibitory therapy in various patient groups. Among the pharmacokinetic characteristics of ACE inhibitors the route of excretion and to a lesser degree the half-life appear to be the most clinically relevant. There is no evidence that being a prodrug offers a significant clinical advantage. The importance of varying tissue penetration also remains to be determined. Knowledge of ACE inhibitor pharmacokinetics is particularly important in patients with renal or hepatic dysfunction in whom the major route of excretion of these agents is impaired. This might also be the case in elderly patients or those with severe congestive heart failure. However, for most ACE inhibitors, major changes in the drug dosage (amount or interval) are necessary only when the glomerular filtration rate falls below 30 ml/min (1.80 L/h). The occurrence of adverse effects due to overdosage or drug interactions may be prevented by adapting the prescription of an ACE inhibitor to its pharmacokinetic characteristics.

Clinical pharmacokinetics of the newer ACE inhibitors. A review

The orally active angiotensin-converting inhibitors (ACE inhibitors) such as captopril and enalapril represent a significant therapeutic advance in the treatment of hypertension and congestive heart failure. Enalapril differs from captopril in several respects. It is a prodrug converted by hepatic esterolysis to the active (but more poorly absorbed) diacid, enalaprilat. Enalaprilat is more potent than captopril, more slowly eliminated and does not possess a sulfhydryl (SH) group. Enalapril was rapidly followed by a number of newer ACE inhibitors, the majority of which are similar to enalapril in that they are prodrugs, converted by hepatic esterolysis to a major active but poorly absorbed diacid metabolite. In one case (delapril) there are 2 active metabolites; in another (alacepril) the prodrug is converted in vivo to captopril. Lisinopril is an exception in that it is an enalaprilat-like diacid but with acceptable oral bioavailability, so that the prodrug route is not employed. The newer ACE inhibitors are at widely different stages of development, and it is not yet clear how many will reach regular clinical use. Of these newer drugs, lisinopril is the longest established and is the subject of the widest published literature. For a number there is as yet little published pharmacokinetic information. A variety of assay methods have been employed to characterise the pharmacokinetics of the ACE inhibitors, including enzymatic techniques, radioimmunoassay and chromatography. The peak plasma concentrations of the prodrugs are generally observed at around 1 hour and those of the diacid metabolites at about 2 to 4 hours. However, there is considerable variation within and between drugs, with benazepril and benazeprilat reaching peak concentrations early and enalapril and enalaprilat typical of later times to peak. Absorption of the active diacids is generally poor, and moderate (typically 30 to 70%) for the prodrugs. The bioavailability of lisinopril is about 25%. It is difficult to talk meaningfully about half-lives of the active drugs. The declines in their plasma concentrations are polyphasic and, if analytical sensitivity allows, active drug may be found at 48 hours or more following administration. This may reflect binding to ACE in plasma. Half-lives of accumulation are of the order of 12 hours; protein binding varies from little (lisinopril) to 90% (benazeprilat). Elimination is mostly renal but there may be biliary elimination for some, such as benazeprilat and fosinopril. The half-lives of the prodrugs are short. Impaired renal function decreases the elimination rate of the diacids.(ABSTRACT TRUNCATED AT 400 WORDS)