The pharmacokinetics of enalapril in hospitalized patients with congestive heart failure

Simultaneously Predicting the Pharmacokinetics of CES1-Metabolized Drugs and Their Metabolites Using Physiologically Based Pharmacokinetic Model in Cirrhosis Subjects

Hepatic carboxylesterase 1 (CES1) metabolizes numerous prodrugs into active ingredients or direct-acting drugs into inactive metabolites. We aimed to develop a semi-physiologically based pharmacokinetic (semi-PBPK) model to simultaneously predict the pharmacokinetics of CES1 substrates and their active metabolites in liver cirrhosis (LC) patients. Six prodrugs (enalapril, benazepril, cilazapril, temocapril, perindopril and oseltamivir) and three direct-acting drugs (flumazenil, pethidine and remimazolam) were selected. Parameters such as organ blood flows, plasma-binding protein concentrations, functional liver volume, hepatic enzymatic activity, glomerular filtration rate (GFR) and gastrointestinal transit rate were integrated into the simulation. The pharmacokinetic profiles of these drugs and their active metabolites were simulated for 1000 virtual individuals. The developed semi-PBPK model, after validation in healthy individuals, was extrapolated to LC patients. Most of the observations fell within the 5th and 95th percentiles of simulations from 1000 virtual patients. The estimated AUC and Cmax were within 0.5-2-fold of the observed values. The sensitivity analysis showed that the decreased plasma exposure of active metabolites due to the decreased CES1 was partly attenuated by the decreased GFR. Conclusion: The developed PBPK model successfully predicted the pharmacokinetics of CES1 substrates and their metabolites in healthy individuals and LC patients, facilitating tailored dosing of CES1 substrates in LC patients.

Enalapril and Enalaprilat Pharmacokinetics in Children with Heart Failure Due to Dilated Cardiomyopathy and Congestive Heart Failure after Administration of an Orodispersible Enalapril Minitablet (LENA-Studies)

Angiotensin-converting enzyme inhibitors (ACEI), such as enalapril, are a cornerstone of treatment for pediatric heart failure which is still used off-label. Using a novel age-appropriate formulation of enalapril orodispersible minitablets (ODMTs), phase II/III open-label, multicenter pharmacokinetic (PK) bridging studies were performed in pediatric patients with heart failure due to dilated cardiomyopathy (DCM) and congenital heart disease (CHD) in five participating European countries. Children were treated for 8 weeks with ODMTs according to an age-appropriate dosing schedule. The primary objective was to describe PK parameters (area under the curve (AUC), maximal concentration (Cmax), time to reach maximal concentration (t-max)) of enalapril and its active metabolite enalaprilat. Of 102 patients, 89 patients (n = 26, DCM; n = 63 CHD) were included in the primary PK endpoint analysis. Rate and extent of enalapril and its active metabolite enalaprilat were described and etiology and age could be identified as potential PK modifying factors. The dosing schedule appeared to be tolerated well and did not result in any significant drug-related serious adverse events. The PK analysis and the lack of severe safety events supports the applied age-appropriate dosing schedule for the enalapril ODMTs.

Clinical Pharmacokinetics of Enalapril and Enalaprilat in Pediatric Patients-A Systematic Review

Purpose: Enalapril has an established safety and efficacy in adults and is used in hypertension, heart failure, and renal failure. In pediatric patients, enalapril is labeled for children with hypertension and used off label in children with heart failure. The systematic literature search aims to assess the current knowledge about enalapril and its active metabolite enalaprilat pharmacokinetics in children as a basis for dose delineation for pediatric patients with heart failure. Methods: A systematic literature review was performed in the PubMed database using relevant keywords. Dose normalization of relevant pharmacokinetic parameters of the identified studies was done for comparison between different diseases and pediatric age groups. Results: The literature search has resulted in three pediatric pharmacokinetic studies of enalapril out of which Wells et al. reported about children with hypertension and Nakamura et al., and Llyod et al. presented data for pediatric heart failure patients. The area under the curve values of enalaprilat in hypertensive pediatric patients increased with respect to the age groups and showed maturation of body functions with increasing age. Dose normalized comparison with the heart failure studies revealed that although the pediatric heart failure patients of > 20 days of age showed the area under the curve a similar to that of hypertensive patients, two pediatric patients of very early age (<20 days) were presented with 5-6-fold higher area under the curve values. Conclusion: Data related to the pharmacokinetics of enalapril and enalaprilat in hypertensive patients and few data for young heart failure children are available. Comparison of dose normalized exposition of the active metabolite enalaprilat indicated similarities between heart failure and hypertensive patients and a potentially high exposition of premature patients but substantially more pharmacokinetic studies are required to have reliable and robust enalapril as well as enalaprilat exposures especially in pediatric patients with heart failure as a basis for any dose delineation.

Just how prevalent are peptide therapeutic products? A critical review

How prevalent are peptide therapeutic products? How innovative are the formulations used to deliver peptides? This review provides a critical analysis of therapeutic peptide products and the formulations approved by the United States Food and Drug administration (FDA), the European Medicines Agency (EMA), and the Japanese Pharmaceuticals and Medical Devices Agency (PMDA). This review also provides an in-depth analysis of dosage forms and administration routes for delivering peptide therapeutics, including injectables, oral dosage forms, and other routes of administration. We discuss the function of excipients in parenteral formulations in detail, since most peptide therapeutics are parenterally administered. We provide case studies of alternate delivery routes and dosage forms. Based on our analysis, therapeutic peptides administered as injectables remain the most commonly used dosage forms, particularly in the form of subcutaneous, intravenous, or intramuscular injections. In addition, therapeutic peptides are formulated to achieve prolonged release, often through the use of polymer carriers. The limited number of oral therapeutic peptide products and their poor absorption and subsequent low bioavailability indicate a need for new technologies to broaden the formulation design space. Therapeutic peptide products may also be delivered through other administration routes, including intranasal, implant, and sublingual routes. Therefore, an in-depth understanding of how therapeutic peptides are now formulated and administered is essential to improve peptide delivery, improve patient compliance, and reduce the healthcare burden for these crucial therapeutic agents.

Pharmacology of enalapril in children: a review

Enalapril is an angiotensin-converting enzyme (ACE) inhibitor that is used for the treatment of (paediatric) hypertension, heart failure and chronic kidney diseases. Because its disposition, efficacy and safety differs across the paediatric continuum, data from adults cannot be automatically extrapolated to children. This review highlights paediatric enalapril pharmacokinetic data and demonstrates that these are inadequate to support with certainty an age-related effect on enalapril/enalaprilat pharmacokinetics. In addition, our review shows that evidence to support effective and safe prescribing of enalapril in children is limited, especially in young children and heart failure patients; studies in these groups are either absent or show conflicting results. We provide explanations for observed differences between age groups and indications, and describe areas for future research.

Acute effects of angiotensin-converting enzyme inhibition versus angiotensin II receptor blockade on cardiac sympathetic activity in patients with heart failure

The beneficial effects of angiotensin-converting enzyme (ACE) inhibitors and angiotensin II (ANG II) receptor antagonists in patients with heart failure secondary to reduced ejection fraction (HFrEF) are felt to result from prevention of the adverse effects of ANG II on systemic afterload and renal homeostasis. However, ANG II can activate the sympathetic nervous system, and part of the beneficial effects of ACE inhibitors and ANG II antagonists may result from their ability to inhibit such activation. We examined the acute effects of the ACE inhibitor captopril (25 mg, n = 9) and the ANG II receptor antagonist losartan (50 mg, n = 10) on hemodynamics as well as total body and cardiac norepinephrine spillover in patients with chronic HFrEF. Hemodynamic and neurochemical measurements were made at baseline and at 1, 2, and 4 h after oral dosing. Administration of both drugs caused significant reductions in systemic arterial, cardiac filling, and pulmonary artery pressures (P < 0.05 vs. baseline). There was no significant difference in the magnitude of those hemodynamic effects. Plasma concentrations of ANG II were significantly decreased by captopril and increased by losartan (P < 0.05 vs. baseline for both). Total body sympathetic activity increased in response to both captopril and losartan (P < 0.05 vs. baseline for both); however, there was no change in cardiac sympathetic activity in response to either drug. The results of the present study do not support the hypothesis that the acute inhibition of the renin-angiotensin system has sympathoinhibitory effects in patients with chronic HFrEF.

High inter-individual variability of vardenafil pharmacokinetics in patients with pulmonary hypertension

PURPOSE

To evaluate the pharmacokinetic parameters of a single oral dose of vardenafil in patients with pulmonary hypertension (PH).

METHODS

Sixteen patients with PH received vardenafil in single oral doses (20, 10 or 5 mg), and repeated blood sampling for up to 9 h was performed. Vardenafil plasma concentration was determined using liquid chromatography tandem mass spectrometry. Pharmacokinetic parameters were calculated using model-independent analysis.

RESULTS

The plasma vardenafil concentration increased rapidly and exhibited a median time to maximum plasma concentration (t(max)) of 1 h and a mean elimination half-life (t(1/2)) of 3.4 h. The geometric mean and standard deviation of (1) the peak plasma concentration (C(max)) was 21.4 ± 1.7 μg/L, (2) the normalized C(max) (C(max, norm)) 79.1 ± 1.6 g/L, (3) the area under the time-concentration curve (AUC) 71.5 ± 1.6 μg · h/L and (4) the normalized AUC (AUC(norm)) 261.6 ± 1.7 g · h/L. Patients co-medicated with bosentan reached t(max) later and had a 90% reduction of C(max), C(max, norm), AUC and AUC(norm).

CONCLUSION

The pharmacokinetic profile of vardenafil overall revealed considerable inter-individual variability in patients with PH. Co-medication with bosentan resulted in a pharmacokinetic drug interaction, leading to significantly decreased plasma concentrations of vardenafil. Therapeutic drug monitoring for individual dose optimization may be warranted.

Drug Absorption in the Management of Congestive Heart Failure: Loop Diuretics

Congestive heart failure is a disease state distinguished by the regular presence of both renal and hepatic abnormalities in drug handling. One such abnormality involves flaws in the process of drug absorption. In most instances, congestive heart failure-related abnormalities in drug absorption are of inconsequential significance. However, this is not the case with loop diuretics. Loop diuretic action ordinarily tracks the rate and extent of absorption if a sufficient amount of diuretic has been given to exceed the threshold for diuretic effect. In congestive heart failure, both the rate and absolute amount of loop diuretic absorbed can be reduced as a function of the heart failure state itself. In this setting, drug dissolution characteristics can assume added significance. Furosemide is the loop diuretic with the widest intra- and interpatient variability of absorption. Alternatively, the loop diuretic torsemide is rapidly and fairly completely absorbed independent of the heart failure state. This pattern of absorption establishes it as the preferred loop diuretic in the otherwise diuretic-resistant heart failure patient. However, the exact role of torsemide in the outpatient management of congestive heart failure remains to be determined.

Determination of enalapril and enalaprilat by enzyme linked immunosorbent assays: application to pharmacokinetic and pharmacodynamic analysis

We have developed two enzyme linked immunosorbent assay (ELISA) methods for determining enalapril and enalaprilat in plasma. In this study, 48 healthy subjects received an oral dose of either 10 or 20 mg of enalapril and plasma concentrations of enalapril and enalaprilat were determined by their specific ELISA methods. These plasma concentrations and blood pressure measurements were applied to evaluate the pharmacokinetic (PK) and pharmacodynamic (PD) parameters of both enalapril and enalaprilat. The enalapril values for the area under the curve (AUC(0)--> infinity ) were 480 +/- 216 and 832 +/- 325 ngh/mL, maximum plasma concentrations (C(max)) were 310 +/- 187 and 481 +/- 185 ng/mL, and times required to reach the maximum concentration t(max) were 1.13 +/- 0.22 and 1.09 +/- 0.33 h for 10 and 20 mg doses, respectively. The enalaprilat values for AUC(0)--> infinity were 256 +/- 122 and 383 +/- 158 ngh/mL, C(max) values were 57 +/- 29 and 72.9 +/- 33.6 ng/mL and t(max) values were 4.28 +/- 1.45 and 4.05 +/- 01.22 h for 10 and 20 mg doses, respectively. The C(max) values of enalapril were approximately 10 times higher than those in the literature, which were determined by angiotensin converting enzyme (ACE) inhibition assays following alkaline hydrolysis, but similar to those of enalaprilat. The PD profiles revealed a significant correlation between enalaprilat concentrations in plasma and the decrease in systolic and diastolic blood pressures (r = -0.95 with P < 0.001 and r = -0.95 with P < 0.001), respectively, following a single oral dose of enalapril. These ELISA methods have the advantage of being simple, accurate, sensitive, and do not depend on enalaprilat binding to ACE. Such methods can be used for analysis and kinetic testing of enalapril and enalaprilat in biological fluids.

A simple HPLC method for quantitation of enalaprilat

A reversed-phase high performance liquid chromatography (HPLC) method with UV-detection has been developed for the determination of enalaprilat. The method produced linear response over the wide concentration range of 1-200 microg/ml, with an average accuracy of 97.35 +/- 4.93%, as well as average intra- and iter-day variations of 3.72 and 5.18%, respectively. The limits of detection and quantitation of the method were 0.125 and 0.5 microg/ml, respectively. The method was selective with respect to resolution of the peaks of enalaprilat and enalapril maleate.

[Conversion from oral ACE inhibitor to intravenous quinaprilat administration in mild to moderate essential hypertension]

AIM

This study was designed to evaluate the efficacy of intravenous quinaprilat in maintaining blood pressure control and to assess the safety of directly switching from oral angiotensin-converting enzyme (ACE) inhibitors to intravenous quinaprilate.

PATIENTS AND METHOD

Following an initial 1-day open-label phase, patients with essential mild to moderate hypertension controlled by ACE inhibitor monotherapy were randomly assigned to treatment with intravenous quinaprilate (n = 36) or oral quinapril (n = 19) for a 3-day double-blind period. Quinaprilate (2.5, 5, or 10 mg BID) and quinapril (10, 20, or 40 mg OD) dosages were based on the patient's previous ACE inhibitor doses. The intravenously used dosages were half the dosages of orally administered enalapril, lisinopril and quinapril. Patients returned to their previous ACE inhibitor therapy during a second 1-day open-label phase.

RESULTS

Quinaprilate and quinapril maintained diastolic blood pressure control at levels comparable to those during the initial open-label ACE inhibitor treatment. The mean difference between quinaprilate and quinapril treatment groups in diastolic blood pressure showed no clinically relevant differences between treatment groups with regard to mean changes from baseline. Mean reductions in systolic blood pressure were similar to those of diastolic blood pressure.

CONCLUSION

Quinaprilate, at half the dose of quinapril, administered BID maintains blood pressure control, is well tolerated, and allows for safe conversion from previously applied oral ACE inhibitors. This finding is important for the antihypertensive treatment of patients in intensive care units or peri/post-operatively who cannot swallow orally administered drugs.

Use of angiotensin-converting enzyme inhibitors as monotherapy and in combination with diuretics and calcium channel blockers

Angiotensin-converting enzyme (ACE) inhibitors have earned an important place in medical therapy since their discovery about two decades ago. This family of drug has grown tremendously since the introduction of captopril in 1981. There are currently more than 14 ACE inhibitors in the world and 9 are available in the United States. Although these agents share many similarities, they differ in their pharmacokinetic properties, approved indications, and cost. This paper provides guidance for selection of ACE inhibitors by examining the pharmacokinetics, pharmacodynamics, drug interactions, adverse effects, and cost of these agents. Combination products of ACE inhibitors with either diuretics or calcium channel blockers also are reviewed.

Pharmacokinetic-pharmacodynamic model relating spiraprilat plasma concentrations to systemic and regional hemodynamic effects in congestive heart failure

The aim of this study was to investigate the relations between the plasma concentrations of spiraprilat (the active metabolite of the angiotensin-converting enzyme inhibitor spirapril) and its effects on plasma converting enzyme activity (PCEA), pulmonary capillary wedge pressure (PCWP), and brachial blood flow (BBF), after a single oral administration of 6 mg of spirapril in eight patients with severe congestive heart failure (CHF). Concentrations and effects were determined before and repeatedly during 48 h after drug intake. A sigmoid model was fitted to individual observations. Maximal effects, concentrations inducing half-maximal effects, and Hill coefficients were -99 +/- 2%, 3.9 +/- 1.9 ng/ml, and 2.4 +/- 0.7 for PCEA inhibition, -15 +/- 8 mm Hg, 11.8 +/- 9.2 ng/ml, and 2.6 +/- 1.3 for PCWP decrease, and 36 +/- 19 ml/min, 13.8 +/- 7.6 ng/ml, and 3.3 +/- 1.0 for BBF increase. In severe CHF, although a 14 ng/ml plasma concentration of spiraprilat may induce a 95% inhibition of PCEA, a 30 ng/ml plasma concentration is mandatory to normalize PCWP and BBF. This concentration corresponds to the peak achieved after a 6-mg oral dose of spirapril.

Cardiorespiratory effects of continuous i.v. administration of the ACE inhibitor enalaprilat in the critically ill

1. Cardiorespiratory effects of long-term, continuous i.v. administration of the ACE inhibitor enalaprilat were studied. 2. Forty-five consecutive critically patients suffering from trauma or postoperative complications were randomly separated into three groups (15 patients in each group) receiving either 0.25 mg h-1 or 0.50 mg h-1 enalaprilat, respectively, or saline solution as placebo (= control group). The infusion was continued for 5 days. 3. Haemodynamic and respiratory parameters were intensively monitored on admission to the intensive care unit (= 'baseline' values) and daily during the next 5 days. 4. Mean arterial blood pressure (MAP) decreased significantly only in the enalaprilat-treated patients, whereas heart rate (HR) remained unchanged in these patients. 5. Pulmonary capillary wedge pressure (PCWP) and pulmonary artery pressure (PAP) were decreased by enalaprilat (0.50 mg h-1: PAP (mean +/- s.d.) decreased from 28.0 +/- 4.1 to 24.0 +/- 3.0 mm Hg) and remained significantly lower than in the control group. In the untreated control group, cardiac index (CI), oxygen consumption (VO2I) and oxygen delivery (DO2I) significantly decreased, which was blunted by enalaprilat infusion. Oxygen extraction (O2-extr) increased in both enalaprilat groups (0.25 mg h-1: from 26.1 +/- 5.5 to 30.4 +/- 4.0%; 0.50 mg h-1: 25.2 +/- 5.6 to 30.9 +/- 4.4%) and decreased in the control patients. 6. Right ventricular haemodynamics improved by enalaprilat infusion (0.50 mg h-1: RVEF increased from 40.0 +/- 3.5 to 45.5 +/- 4.0%). Lactate plasma concentrations decreased in the group with 0.50 mg h-1 enalaprilat (from 1.9 +/- 1.0 to 1.3 +/- 0.3 mg dl-1) and increased in the control patients. 7. Continuous infusion of the ACE inhibitor enalaprilat exerted beneficial cardiorespiratory effects in the critically ill. The widespread common risk of altered perfusion with decreased CI, DO2, VO2, O2-extr and increased lactate concentration was blunted by enalaprilat infusion. 8. Although 0.5 mg h-1 enalaprilat was most effective, a dose of 0.25 mg h-1 also showed beneficial haemodynamic effects in the critically ill.

Pharmacokinetic changes in patients with oedema

The pharmacokinetics of furosemide (frusemide) in patients with oedema have been relatively well studied, but in many studies it is unclear whether the disease or the oedema per se has the major effect. The rate of absorption of oral furosemide in patients with oedema was decreased, but total bioavailability was almost unchanged. The peak serum concentration (Cmax) and time taken to achieve Cmax were either decreased or unchanged. Binding of furosemide to plasma proteins is lower in patients with congestive heart failure (CHF), decompensated liver cirrhosis (DLC) and nephrotic syndrome, probably as a result of hypoalbuminaemia. The elimination half-life (t1/2) can be unchanged (CHF, DLC) or prolonged (chronic renal failure: CRF). Plasma and renal clearance are reduced in patients with CRF and nephrotic syndrome, but are almost unchanged in CHF and DLC. Disease-induced disorders are mainly responsible for the alterations of furosemide pharmacokinetics in oedematous conditions, while the influence of oedema per se is probably not clinically relevant. The pharmacokinetics of digoxin have been studied in a small number of studies only. In patients with CHF, considerable interindividual differences have been found. Because digoxin has a narrow therapeutic window, this drug should be administered cautiously to oedematous patients. Theophylline has higher bioavailability in patients with oedema, with a significantly higher Cmax in patients with hepatic cirrhosis and CHF than in healthy volunteers (29 and 22%, respectively). Furthermore, clearance decreases and t1/2 increases in these patients. Angiotensin converting enzyme (ACE) inhibitors are often administered as prodrugs, and their pharmacokinetic profile could be influenced by the diseases that accompany oedematous states. However, the effect of oedema is difficult to discriminate from that of the disease. Individual ACE inhibitors are affected differently, but importantly the dosage of perindopril should be reduced in patients with CHF, while for most other ACE inhibitors the changes in pharmacokinetic parameters are clinically irrelevant. In conclusion, studies on pharmacokinetic changes in oedema are limited. Besides affecting absorption (after oral administration) and conversion of the prodrug to the active form, probably as a result of the associated disease, oedema has not been proven to cause any clinically relevant changes in pharmacokinetic parameters for individual drugs. However, further studies of this aspect of pharmacokinetics are needed.

Isolated circulatory response to intravenous administration of the ACE inhibitor enalaprilat

The isolated vascular effects of intravenous administration of the angiotensin converting enzyme (ACE) inhibitor enalaprilat were investigated. Thirty male patients undergoing cardiopulmonary bypass (CPB) were studied. According to a randomized sequence, 0.04 mg kg-1 enalaprilat (low-dose, n = 10), 0.08 mg kg-1 (high-dose, n = 10) enalaprilat or saline solution as placebo (control group, n = 10) was given as an i.v. bolus during CPB. Changes in mean arterial pressure (MAP) and venous reservoir (RV) of the extracorporeal circulation were studied as indices of arterial resistance and venous capacitance. Mean arterial blood pressure (MAP) and peripheral vascular resistance (SVR) were significantly more reduced in the high-dose enalaprilat group (MAP: -36 mm Hg after 9 min; SVR: -836 dyn s cm-5) than in the low-dose group (MAP: -13 mm Hg after 10 min). Volume of the reservoir (RV) decreased in both enalaprilat treated groups indicating additional (dose-dependent) venous pooling effects of the substance (low-dose: -300 ml; high-dose: -520 ml; control group: -100 ml). Skin capillary blood flow measured by laser Doppler flowmetry (LDF) increased after injection of 0.04 mg kg-1 enalaprilat, whereas it decreased significantly when MAP fell markedly in patients treated with high-dose enalaprilat. I.v. enalaprilat had dose-dependent vasodilating properties in the arterial and venous vessel system indicating reduction in pre- and afterload. Microcirculation in both enalaprilat treated groups improved as long as reduction in blood pressure was not limited.

The pharmacokinetics of quinapril and quinaprilat in patients with congestive heart failure

The pharmacokinetics of quinapril and its active metabolite quinaprilat were studied in 12 patients with congestive heart failure (CHF) after multiple oral doses of 10 mg quinapril twice daily. Six patients had an ejection fraction of < 35% and six had an ejection fraction between 35%-50%. Increases in the apparent elimination half-life and in AUC(0, 12h) values of quinaprilat were associated with smaller ejection fractions, decreased creatinine clearance, and increased patient age. Comparison with data from age-matched controls having comparable renal function suggests that creatinine clearance is the major determinant of quinaprilat clearance. CHF per se appears to have minimal effect. Dosing of quinapril in patients with CHF should be based on their renal function.

Enalapril clinical pharmacokinetics and pharmacokinetic-pharmacodynamic relationships. An overview

The conventional pharmacokinetic profile of the angiotensin converting enzyme (ACE) inhibitor, enalapril, is a lipid-soluble and relatively inactive prodrug with good oral absorption (60 to 70%), a rapid peak plasma concentration (1 hour) and rapid clearance (undetectable by 4 hours) by de-esterification in the liver to a primary active diacid metabolite, enalaprilat. Peak plasma enalaprilat concentrations occur 2 to 4 hours after oral enalapril administration. Elimination thereafter is biphasic, with an initial phase which reflects renal filtration (elimination half-life 2 to 6 hours) and a subsequent prolonged phase (elimination half-life 36 hours), the latter representing equilibration of drug from tissue distribution sites. The prolonged phase does not contribute to drug accumulation on repeated administration but is thought to be of pharmacological significance in mediating drug effects. Renal impairment [particularly creatinine clearance < 20 ml/min (< 1.2 L/h)] results in significant accumulation of enalaprilat and necessitates dosage reduction. Accumulation is probably the cause of reduced elimination in healthy elderly individuals and in patients with concomitant diabetes, hypertension and heart failure. Conventional pharmacokinetic approaches have recently been extended by more detailed descriptions of the nonlinear binding of enalaprilat to ACE in plasma and tissue sites. As a result of these new approaches, there have been significant improvements in the characterisation of concentration-time profiles for single-dose administration and the translation to steady-state. Such improvements have further importance for the accurate integration of the pharmacokinetic and pharmacodynamic responses to enalapril(at) in a concentration-effect model.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug-patient interactions and their relevance in the treatment of heart failure

The effects of congestive heart failure (CHF) on drug disposition and elimination are many and varied. Indeed, the pharmacokinetics of many of the drugs used to treat CHF are significantly altered by the patient's underlying condition. Reduced gastric emptying in CHF delays absorption and decreases the peak plasma concentrations of furosemide, bumetanide, and digoxin. Moreover, drugs that have a high hepatic extraction ratio (organic nitrates, morphine, prazosin, and hydralazine) achieve higher than expected plasma concentrations in patients with CHF. In contrast, drugs requiring biotransformation to active forms, e.g., angiotensin-converting enzyme (ACE) inhibitors such as enalapril, perindopril, quinapril, and ramipril, generally have lower than expected plasma concentrations. Nevertheless, ACE inhibitors can impair renal function in CHF, leading to an actual increase in plasma concentrations. However, decreases in absorption and first-pass metabolism are often offset by reduced hepatic and renal clearance. The overall absorption of lisinopril may be reduced in some CHF patients; consequently, the onset of effect is delayed but is often more prolonged.

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.

Renal toxicity of enalapril in very elderly patients with progressive, severe congestive heart failure

We evaluated the safety of enalapril administration in 20 very old (76 +/- 7 years) patients with rapidly progressive congestive heart failure (deteriorating from New York Heart Association class 2 to class 4 on admission). They were all given increasing doses of enalapril regardless of concomitant diuretic therapy and state of hydration. Renal function deteriorated in four patients (group A) and remained unchanged in 16 (group B). The mean pretreatment serum creatinine level in group A was significantly higher than that in group B (2.4 vs 1.3 mg/dl, p less than 0.001). No patient with a serum creatinine level less than 1.9 mg/dl on admission had further impairment of renal function. Groups A and B did not differ by age, concomitant diseases (including hypertension and diabetes mellitus), or medications (including diuretics) or by in-hospital serum electrolyte concentrations and blood pressure. Renal damage was noted during the initial four days of the study and was reversible following discontinuation of enalapril. Our data suggest that enalapril can be safely administered to very old patients with rapidly progressive congestive heart failure provided that the initial serum creatinine level is below 1.9 mg/dl. In patients with a higher serum creatinine level, careful monitoring and prompt discontinuation of enalapril administration can prevent irreversible renal damage.

Initial and steady state pharmacokinetics of cilazapril in congestive cardiac failure

Twenty one patients with NYHA class II-III congestive heart failure received single ascending doses of 0.5, 1.25 and 2.5 mg cilazapril daily followed by the minimum effective dose for six weeks. Fifteen patients completed the study, but the data from only 11 were sufficiently complete for kinetic evaluation. The pharmacokinetics of the metabolite, cilazaprilat, after a single dose of 0.5 mg cilazapril were similar to previous observations in healthy volunteers at identical dosage. Repeat administration, however, led to greater accumulation than previously observed in volunteers at the higher dosages of 1.25 or 5 mg given for 8 days. Seven patients experienced adverse events. Four were severe, leading to withdrawal of the patients from the study, but only one event was related to cilazapril. Of the other three, one suffered a myocardial infarction and subsequently died due to worsening congestive heart failure. One other patient was withdrawn with two adverse events probably related to cilazapril. No other deaths occurred amongst the study population, and there were no significant abnormalities in haematology or blood chemistry.

Short term haemodynamic effects of converting enzyme inhibition before and after eating in patients with moderate heart failure caused by dilated cardiomyopathy: a double blind study

The haemodynamic changes that follow a meal can mimic the response to a vasodilator drug. To avoid overestimating the beneficial effects of treatment in uncontrolled studies, measurements of haemodynamic function are usually performed with patients in the fasting postabsorptive state. But such recordings are not representative of the resting patient during daily life. In this double blind placebo controlled study the short term haemodynamic effects of enalapril were assessed during 12 hours in 19 patients with moderate heart failure caused by dilated cardiomyopathy. The patients ate lunch and dinner and were studied in the absorptive and postabsorptive phases. In the placebo group systemic vascular resistance, mean arterial pressure, and the rate-pressure product fell significantly (5-16%) after lunch. Four hours after lunch the haemodynamic function had returned to baseline--that is the postabsorptive state. Enalapril, accentuated the haemodynamic effects during the absorptive state producing a larger post-prandial fall in mean arterial blood pressure and rate-pressure product and changes in the absorptive phase were maintained into the post-absorptive phase. Pulmonary wedge pressure fell significantly after treatment with enalapril. These overall changes during the study period indicated that enalapril reduced the preload and afterload on the heart--over and above the reduction produced by eating. These findings suggest that the effects of enalapril given at rest to patients with moderate heart failure unload the heart and enhance the reduction of afterload induced by meals.

Perindopril. A review of its pharmacokinetics and clinical pharmacology

Perindopril is an orally active, non-thiol angiotensin-converting enzyme (ACE) inhibitor, which in doses of 4 to 8mg is effective in the control of essential hypertension. As monotherapy it is as effective as once-daily atenolol and possibly more effective than twice-daily captopril. A synergistic response has been noted when perindopril is combined with a thiazide diuretic. Maximal pharmacodynamic effects (ACE inhibition, increase in plasma renin activity and angiotensin I, reduction in aldosterone and angiotensin II and blood pressure) are seen 4 to 6 hours after dosing, with substantial effects still present at 24 hours. Perindopril is a prodrug which requires de-esterification to perindoprilat for useful ACE inhibition. Maximal plasma perindoprilat concentrations are reached 2 to 6 hours after oral administration of perindopril, and 70% of the active metabolite is cleared by the kidneys. The other major metabolite of perindopril is an inactive glucuronide. Ageing is associated with increased serum perindoprilat concentrations, which are probably caused by a combination of enhanced conversion to the active metabolite and diminished renal clearance. Compensated cirrhosis does not appear to have an independent effect. There is little published experience of the use of perindopril in patients with cardiac failure or other cardiac disease, but preliminary evidence would support the general value of this class of agent as adjunctive therapy.

The pharmacokinetics of lisinopril in hospitalized patients with congestive heart failure

1. The pharmacokinetics of the angiotensin converting enzyme inhibitor, lisinopril, were studied in an open, randomized, balanced, two-period, crossover design in 12 in-patients with stable, chronic congestive heart failure (CHF). 2. To evaluate the pharmacokinetics of lisinopril in CHF, lisinopril was administered orally (10 mg) and intravenously (5 mg) in each patient. Each dose was followed by a 72 h period with frequent blood sampling and fractional urine collections for radioimmunoassay of lisinopril. 3. Mean urinary recovery of lisinopril was 15 and 88% following oral and intravenous administration, respectively; absorption/bioavailability of lisinopril based on urinary recovery ratios was 16%, less than that found in normal subjects. 4. Serum concentrations of lisinopril following intravenous administration were higher in this study than those previously observed in normal subjects. 5. The results of this study suggest a reduced absorption of lisinopril in CHF and altered disposition, possibly associated with age as well as the disease state.

Enalapril. An update of its pharmacological properties and therapeutic use in congestive heart failure

Enalapril provides significant haemodynamic, symptomatic and clinical improvement when added to maintenance therapy with digitalis and diuretics in patients with congestive heart failure [NYHA (New York Heart Association) classes II to IV]. These effects are not attenuated during long term therapy. More significantly, a clinical study demonstrated that enalapril reduces mortality when added to established therapy in patients with severe congestive heart failure (NYHA class IV) refractory to digitalis, diuretics and other vasodilators. Thus, ACE inhibitors such as enalapril offer a significant advance in the treatment of congestive heart failure. Because these drugs improve symptoms in patients with classes II to IV failure, and reduce mortality in patients with severe heart failure, they should be considered as first choice adjuvant therapy when a vasodilator is needed in addition to conventional treatment with digitalis and diuretics.

A pharmacokinetic study of cilazapril in patients with congestive heart failure

1. The pharmacokinetics of cilazapril and the inhibition of angiotensin converting enzyme (ACE) were investigated in 10 patients with congestive heart failure, NYHA class II-III, receiving diuretics with or without digoxin. 2. Patients received 0.5 mg and 1 mg cilazapril on the first 2 days, followed by 0.5 mg or 1 mg daily for the next 8 weeks, in a single-blind study. Plasma cilazaprilat concentrations and plasma ACE activities were measured by radioenzymatic methods up to 24 h after the first and last doses. 3. After the initial 0.5 mg dose of cilazapril, a mean maximum plasma concentration of cilazaprilat of 6.8 ng ml-1 was observed at 2.3 h. Concentrations declined up to 8 h with a mean half-life of 5.8 h, followed by slower decrease to 24 h. Total clearance, based on data to 24 h, was estimated at 8.5 l h-1, with three-fold inter-individual variation. Mean maximum plasma ACE inhibition was 87%, decreasing to 65% at 24 h. 4. In the multiple dose phase of the study, four patients received cilazapril 0.5 mg daily, and six patients 1 mg daily. Cilazapril accumulation for the 0.5 mg group averaged 77%, but steady state concentrations for the 1 mg group were less than double those of the 0.5 mg group. ACE inhibition profiles at steady state were similar for both groups, and they differed from first dose data only in a somewhat lower inhibition at 24 h. 5. Historical comparison of the first-dose data with those for healthy young volunteers at identical dosage revealed only minor differences in kinetic parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-converting enzyme inhibitors. Relationship between pharmacodynamics and pharmacokinetics

The inter-relationship between the pharmacokinetic and pharmacodynamic behaviour of ACE inhibitors is reviewed. First, some of the methods which have been used to assess the pharmacodynamics of ACE inhibitors in humans are presented. They include humoral assays (e.g. ACE activity in plasma, renin activity, etc.), haemodynamic changes (blood pressure, total peripheral resistance, etc.) and agonist challenges (angiotensin I infusions). Subsequently a pharmacokinetic-dynamic model is described, based on biochemical processes obtained after ACE inhibition, which seems to be useful for the interpretation of the complex processes. The various correlations between plasma drug concentration on the one hand and plasma ACE activity, angiotensin II concentration in plasma or blood pressure on the other, are discussed on the basis of this model. From the model obtained it becomes obvious that under many circumstances the release of the inhibitor from ACE binding is the step which in fact determines the pharmacodynamically relevant elimination rate of the drug at low concentrations, whereas at high concentrations the elimination of the drug is mainly dependent on kidney (and/or liver) elimination rate. The dynamic-kinetic correlations are then presented for some ACE inhibitors in various disease states: arterial hypertension, heart failure, old age, renal failure, liver disease. In a final section the kinetic and dynamic relevance of interactions of ACE inhibitors with food and other drugs is described (e.g. prostaglandin inhibitors, diuretics, digoxin and cimetidine). Despite the great body of literature which deals with the kinetic and/or dynamic properties of ACE inhibitors, precise knowledge of the relationship between their kinetic and dynamic behaviour is rather limited and there is a clear need for further studies to elucidate this complex topic, thereby improving therapeutic possibilities with these useful new compounds.

Clinical pharmacokinetics in heart failure. An updated review

Pharmacokinetics is the study of the effect that the body has on drug absorption, distribution, metabolism and excretion. The pharmacokinetics of a specific drug are assessed by the volume of distribution, bioavailability, clearance and elimination half-life. Elimination half-life is directly related to the volume of distribution and inversely related to clearance. Any 1 or more of these parameters may be altered by physiological changes such as ageing, or disease states such as congestive heart failure. Congestive heart failure is associated with hypoperfusion to various organs including the sites of drug clearance, i.e. the liver and kidneys. It also leads to organ congestion as seen in the liver and gut. The main changes in drug pharmacokinetics seen in congestive heart failure are a reduction in the volume of distribution and impairment of clearance. The change in elimination half-life consequently depends on whether both clearance and the apparent volume of distribution change, and the extent of that change. Pharmacokinetic changes are not always predictable in congestive heart failure, but it seems that the net effect of reduction in the volume of distribution and impairment of clearance is that plasma concentrations of drugs are usually higher in patients with congestive heart failure than in healthy subjects. The changes in pharmacokinetics assume importance only in the case of drugs with a narrow therapeutic ratio (e.g. digoxin) and some of the antiarrhythmics such as lignocaine (lidocaine), procainamide and disopyramide. This necessitates reduction in both the loading and maintenance doses. Prolongation of the elimination half-life leads to delay in reaching steady-state, and therefore dose increments must be made more gradually. Plasma concentration measurements of the drugs concerned are a good guide to therapy and help to avoid toxicity. Pharmacokinetic changes are of less importance in the case of drugs with immediate clinical response, e.g. diuretics and intravenous vasodilators such as nitrates and phosphodiesterase inhibitors. The dose in the latter group can be titrated to the desired effect. Not all adverse reactions to drugs that may occur in heart failure are the result of alterations in pharmacokinetics; rather, some may be due to important drug interactions. An interaction may occur directly e.g. reduction of renal clearance of digoxin by captopril and quinidine; or indirectly, e.g. through diuretic-induced hypokalaemia, which exacerbate arrhythmias associated with digoxin and antiarrhythmics such as quinidine and procainamide.

Evaluation of the safety of enalapril in the treatment of heart failure in the very old

We have introduced enalapril, in doses equal to or less than the 2.5 mg currently recommended, as an adjuvant to digoxin and diuretics in 17 patients of mean (SD) age 83 (5) years with severe heart failure. Only eleven patients tolerated its introduction. Unlike those reported in younger patients, all but one of the adverse drug reactions occurred 8 h or more after the first dose. Aged patients started on ACE inhibitors should be observed in hospital until stabilized on a maintenance dose. Three patients had an adverse reaction which differed in nature from those previously reported: acute confusional state, ataxia and mesenteric ischaemia. Ten patients were discharged on 5 mg or 10 mg maintenance doses of enalapril. In nine of them improvement on triple therapy was sustained for a minimum of three months. ACE inhibition was lost in the other patient when her compliance with enalapril therapy fell to around 75%: monitoring compliance is essential when ACE inhibitors are used in low dosages. Enalapril was withdrawn during follow up in three patients because of symptoms of mesenteric ischaemia and in four because of dramatic deterioration of renal function. One of the latter was found subsequently to have severe bilateral atheromatous renal artery stenosis. When isosorbide dinitrate was substituted for enalapril, symptoms of mesenteric ischaemia resolved and renal function returned to baseline. Continuing surveillance for adverse effects is essential in patients of this age group with severe heart failure, and the risk of occult renal artery stenosis requires regular biochemical screening during follow up.(ABSTRACT TRUNCATED AT 250 WORDS)