Pharmacokinetics of the angiotensin converting enzyme inhibitor benazepril.HCl (CGS 14 824 A) in healthy volunteers after single and repeated administration

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.

Benefit and risk evaluation of quinapril hydrochloride

INTRODUCTION

Angiotensin-converting enzyme (ACE) inhibitors are a mainstay of antihypertensive therapy. Quinapril hydrochloride, a less commonly used, and less-studied ACE inhibitor has been approved for its primary use in hypertension. Studies also indicate its off-label use for congestive heart failure and diabetic nephropathy. The ANDI and TREND trials have been pivotal in demonstrating the effectiveness of quinapril.

AREAS COVERED

The authors conducted a review of the literature analyzing the clinical efficacy and safety profile of quinapril. This review discusses the development of quinapril, provides an updated summary of the indications and contraindications, and presents a comparison with other ACE inhibitors.

EXPERT OPINION

Quinapril is a safe and well-tolerated antihypertensive medication with a favorable safety profile compared to other ACE inhibitors. However, a lack of ample recent clinical trials and post-marketing data investigating the efficacy of quinapril in large cohorts has resulted in limited use in clinical practice. Quinapril may be an effective antihypertensive option for elderly populations as well as those who cannot tolerate the side effects profiles of other ACE inhibitors and as an additional treatment option for patients with heart failure with preserved ejection fraction.

Antihypertensive and organ-protective effects of benazepril

Benazepril is a nonsulfhydryl ACE inhibitor with favorable pharmacodynamic and pharmacokinetic properties, well-established antihypertensive effects and a good tolerability profile. Recent clinical studies have demonstrated that patients treated with benazepril alone or in combination with hydrochlorothiazide or amlodipine may achieve beneficial renal outcomes that extend beyond blood pressure control. Furthermore, the recent Avoiding Cardiovascular Events Through Combination Therapy in Patients Living with Systolic Hypertension (ACCOMPLISH) trial showed decreased cardiovascular morbidity and mortality with benazepril when administered as a cotreatment. An additional novel therapeutic area for benazepril is atrial fibrillation. Differences between combination therapies have implications for which patients may be best suited to particular interventions, and further studies are required to fully ascertain this potential.

Development and validation of a liquid chromatographic/electrospray ionization mass spectrometric method for the determination of benazepril, benazeprilat and hydrochlorothiazide in human plasma

A new method was developed and fully validated for the quantitation of benazepril, benazeprilat and hydrochlorothiazide in human plasma. Sample pretreatment was achieved by solid-phase extraction (SPE) using Oasis HLB cartridges. The extracts were analysed by high-performance liquid chromatography (HPLC) coupled to a single-quadrupole mass spectrometer (MS) with an electrospray ionization interface. The MS system was operated in selected ion monitoring (SIM) modes. HPLC was performed isocratically on a reversed-phase porous graphitized carbon (PGC) analytical column (2.1 x 125.0 mm i.d., particle size 5 microm). The mobile phase consisted of 55% acetonitrile in water containing 0.3% v/v formic acid and pumped at a flow rate of 0.15 ml min(-1). Chlorthalidone was used as the internal standard (IS) for quantitation. The assay was linear over a concentration range of 5.0-500 ng ml(-1) for all the compounds analysed, with a limit of quantitation of 5 ng ml(-1) for all the compounds. Quality control (QC) samples (5, 10, 100 and 500 ng ml(-1)) in five replicates from three different runs of analyses demonstrated intra-assay precision (coefficient of variation (CV) < or =14.6%), inter-assay precision (CV < or = 5.6%) and overall accuracy (relative error less than -8.0%). The method can be used to quantify benazepril, benazeprilat and hydrochlorothiazide in human plasma, covering a variety of pharmacokinetic or bioequivalence studies.

Functional Half-Life is a Meaningful??Descriptor of Steady-State??Pharmacokinetics of??an??Extended-Release Formulation of??a??Rapidly Cleared Drug

BACKGROUND

For many drugs, steady-state concentration-time profiles are often not optimally characterised by the intrinsic terminal elimination half-life for various reasons, including multiexponential disposition with minimal contribution of the terminal phase to steady-state exposure or use of controlled-release formulations with extended zero- or mixed zero-/first-order absorption. In such cases, 'effective' or 'functional' half-life (t((1/2)F)) has often been used to characterise steady-state pharmacokinetics. Valproic acid, commonly used in neuropsychiatry, has an elimination half-life of 4-16 hours in different populations (children vs adults, enzyme-induced vs uninduced). Divalproex-ER, a once-daily extended- release divalproex sodium formulation, is designed to release valproic acid over >18 hours. Hence the steady-state divalproex-ER concentration-time profiles have small peak-trough fluctuations that are not optimally characterised by valproic acid elimination half-life. In this study, the value of t((1/2)F) was calculated to characterise divalproex-ER steady-state concentration-time profiles.

METHODS

The value of t((1/2)F), defined as the time taken for the concentration to drop by one-half during a dosing interval (tau) at steady state, was derived using steady-state maximum (C(max)) and minimum (C(min)) plasma concentration and tau values, and calculated as ln(2)/(ln [C(max)/C(min)]/tau). The t((1/2)F) values of valproic acid in adult hepatic enzyme-uninduced healthy subjects and enzyme-induced epilepsy patients were calculated from five pharmacokinetic studies in which divalproex-ER was administered once daily for 6-14 days.

RESULTS

The estimated geometric mean t((1/2)F) in uninduced adults was 40.0 hours versus the expected elimination half-life of 12-16 hours in this population (including patients on valproic acid monotherapy); for induced patients, t((1/2)F) was 26.9 hours versus the expected elimination half-life of 6-12 hours.

CONCLUSION

The t((1/2)F) of valproic acid optimally characterises the expected steady-state C(max) to C(min )decrease of 33% in uninduced and 45% in induced adults following once-daily administration of divalproex-ER.

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%.

Amlodipine/benazepril: fixed dose combination therapy for hypertension

Myocardial infarction, stroke, heart failure and end-stage renal disease have all been linked to inadequate control of blood pressure. Despite overwhelming evidence that uncontrolled hypertension is responsible for a sizeable number of adverse health-related outcomes, control of the disease remains considerably suboptimal. Available data demonstrate that in order to achieve adequate blood pressure control, a large number of patients require therapy with more than one medication. Fixed dose combination antihypertensive therapy has many advantages over other treatment options. Positive effects on blood pressure control, rates of adherence, adverse effects and cost have been identified. Amlodipine/benazepril (Lotrel), Novartis) is a fixed dose combination product indicated for the treatment of hypertension. Although not currently recommended as first-line therapy, studies confirm that this combination of a long-acting calcium antagonist and an angiotensin-converting enzyme (ACE) inhibitor possesses substantial blood pressure lowering capabilities. Whereas adverse events tend to become more frequent with increasing doses of antihypertensive monotherapy, the rate of adverse events attributed to amlodipine/benazepril in clinical trials often correlates with rates ascribed to placebo. Amlodipine/benazepril is capable of sustaining blood pressure control over a 24 h period and appears to be minimally affected by an occasional dose omission. Unlike the older calcium antagonists, amlodipine is unlikely to cause alterations in myocardial contractility. Additionally, the amlodipine/benazepril combination product costs less than the same therapy administered as the individual components. It is, therefore, reasonable to consider therapy with amlodipine/benazepril in appropriate patients after an adequate trial of antihypertensive monotherapy.

Plasma angiotensin converting enzyme activity and pharmacokinetics of benazepril and benazeprilat in cats after single and repeated oral administration of benazepril.HCl

The plasma pharmacokinetics of benazepril and its active metabolite, benazeprilat, were determined in cats after oral administration of benazepril.HCl at dosages of 0.25, 0.5 and 1.0 mg/kg as a single dose (n = 5 per group) and after once daily application for 8 days (n = 6 per group). Pharmacodynamics were assessed by measurement of plasma angiotensin converting enzyme (ACE) activity. After single administration of benazepril.HCl, maximum benazepril concentrations were recorded at the first sample (2 h) and declined relatively rapidly with an elimination half life (t1/2) of 1.4 h. Highest benazeprilat concentrations were recorded at the first sample (2 h) in most cats and declined biphasically with half lives of each phase of 2.4 and 27.7 h. With repeated administration, plasma benazeprilat concentrations accumulated slightly with accumulation ratios (R) of 1.46, 1.36 and 1.24 for the 0.25, 0.5 and 1.0 mg/kg dosages of benazepril.HCl, respectively (median value of 1.36 for all dosages). All three dosages of benazepril.HCl caused marked inhibition of plasma ACE activity in all cats. The maximum effect (Emax, % inhibition of ACE as compared to baseline) was > or = 98% after single and 100% with repeated administration. The duration of action of benazepril.HCl was long, with > 87% (single) and > 90% (repeat) inhibition of plasma ACE persisting 24 h after dosing. Benazepril.HCl was well tolerated in all animals. Dosages of 0.25-1.0 mg/kg benazepril.HCl once daily are recommended for clinical testing in cats.

A double-blind, placebo-controlled, ascending-dose evaluation of the pharmacokinetics and tolerability of modafinil tablets in healthy male volunteers

A randomized, double-blind, placebo-controlled, ascending-dose study was conducted to evaluate the pharmacokinetic and safety profiles of increasing modafinil doses (200 mg, 400 mg, 600 mg, 800 mg) administered orally over a 7-day period in normal healthy male volunteers. Eight subjects (six modafinil; two placebo) were randomized to each of the four dose groups. Modafinil or a placebo was administered once daily for 7 days. Serial blood samples were obtained following administration of the day 1 and day 7 doses for characterization of pharmacokinetics, and trough samples were obtained prior to dosing on days 2 through 6 to assess the time to reach the steady state. Pharmacokinetic parameters were calculated using noncompartmental methods. Modafinil steady state was reached after three daily doses. Modafinil pharmacokinetics were dose and time independent over the range of 200 mg to 800 mg. Steady-state pharmacokinetics of modafinil were characterized by a rapid oral absorption rate, a low plasma clearance of approximately 50 mL/min, a volume of distribution of approximately 0.8 L/kg, and a long half-life of approximately 15 hr. Modafinil was primarily eliminated by metabolism. Modafinil acid was the major urinary metabolite. Stereospecific pharmacokinetics of modafinil were demonstrated. The d-modafinil enantiomer was eliminated at a threefold faster rate than 1-modafinil. Modafinil 200 mg, 400 mg, and 600 mg doses were generally well tolerated. The modafinil 800 mg dose panel was discontinued after 3 days of treatment due to the observation of increased blood pressure and pulse rate. The safety data from this study suggest that the maximum tolerable single daily oral modafinil dose, without titration, may be 600 mg.

Pharmacokinetics of the angiotensin-converting-enzyme inhibitor, benazepril, and its active metabolite, benazeprilat, in dog

1. The pharmacokinetics of the angiotensin-converting-enzyme (ACE) inhibitor benazepril were evaluated in eight healthy Beagle dogs. Benazepril was administered orally at a dosage of 7.5 mg (about 0.5 mg/kg) both as a single dose and then once daily for 14 consecutive days. The prodrug, benazepril, and its active metabolite, benazeprilat, were measured in plasma using a gas chromatography mass-spectrometry method with mass-selective detection. 2. Benazepril appeared quickly in the plasma (tmax 0.5 h) and was rapidly eliminated by metabolism to benazeprilat. Peak benazeprilat concentrations were attained later (tmax 1.25 h) and declined biphasically with a rapid elimination phase (t1/2 lambda 1 1.1 and 1.7 h after single and the last repeated dose respectively) followed by a terminal elimination phase (t1/2 lambda z 11.7 and 19.0 h after single and repeated dose respectively). The mean residence time for benazeprilat was 15.2 h after the single dose and 17.4 h after the 14th dose. 3. Repeated administration of benazepril produced moderate bioaccumulation of benazeprilat; the ratio of AUC[0-->24 h]'s after the 14th dose as compared with the single dose was 1.47, equivalent to a half-life for accumulation (t1/2acc) of 14.6 h. Steady-state benazeprilat concentrations at peak (Cmax) and trough (Cmin) were reached within three doses. 4. The pharmacodynamics of benazepril were assessed by measurement of plasma ACE activity. After both single doses and at steady-state, benazepril produced inhibition of ACE activity in all dogs that was maximal at peak effect (Emax = 100%) and long-lasting (> 85% inhibition was present at 24 h). The long duration of action of benazepril on plasma ACE is due to the presence of the terminal elimination phase of benazeprilat, even though most of the metabolite is rapidly eliminated from the plasma.

The absence of a pharmacokinetic interaction between aspirin and the angiotensin-converting enzyme inhibitor benazepril in healthy volunteers

Potential effects of the coadministration of single doses of aspirin (325 mg) and of benazepril hydrochloride (20 mg) on the pharmacokinetics and the metabolism of these two drugs were evaluated in 12 healthy subjects. Plasma concentration profiles of benazepril, its active metabolite benazeprilat, and total salicylic acid were determined together with urinary excretion of benazeprilat, salicylic acid, salicyluric acid, and salicylate glucuronides. Almost superimposable plasma profiles of benazepril, benazeprilat, and total salicylic acid were achieved with the drugs given alone and concomitantly. The coadministration of benazepril hydrochloride and aspirin did not modify the pharmacokinetics or the metabolism of the two drugs.

Site-differential gastrointestinal absorption of benazepril hydrochloride in healthy volunteers

The absorption of benazepril-HCl (BZPH), an orally active angiotensin-converting enzyme (ACE) inhibitor, in various regions of the gastrointestinal (GI) tract was investigated using an intestinal intubation technique. Thirteen subjects completed this single-dose, three-phase sequential crossover study. The drug (20 mg) was administered either as a 4-hr colonic infusion (COLON) or as a small intestinal infusion (SI) in the first two phases and as an oral bolus solution (ORAL) in the third phase, with a 2-week washout between each treatment. Serial plasma and urine samples were collected for up to 4 days after dosing. BZPH and its active metabolite benazeprilat (BZPL) were determined using a gas chromatography/mass spectrometry method. BZPH was absorbed rapidly into the bloodstream (Tmax = 0.5 hr after ORAL). Absorption was also rapid for SI, with a postinfusion half-life (0.57 hr) nearly identical to that for ORAL (0.59 hr). The absorption rate after COLON was much slower (lower Cmax and longer Tmax) compared to that after SI, and the apparent half-life (1.7 hr) was prolonged. SI delivered 90%, whereas COLON delivered 23%, of the drug into the systematic circulation as compared to ORAL. BZPL was rapidly formed upon drug absorption. The metabolite-to-drug AUC ratios were comparable for SI and ORAL (8.9 vs 9.7), indicating that first-pass metabolism of BZPH was neither saturable nor input rate dependent. The metabolite-to-drug AUC ratio was reduced for COLON (5.0), indicating that the mechanism of absorption of BZPH in the colon may be different than that after SI and ORAL. Urinary recovery data were consistent with plasma data.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and pharmacodynamics of benazepril hydrochloride in patients with major proteinuria

We have investigated whether the pharmacokinetics and pharmacodynamics of the ACE inhibitor benazepril hydrochloride are altered with proteinuria by studying 8 patients with major proteinuria of different causes who were given a single dose of 10 mg p.o. The maximum plasma concentration of benazepril was found between 0.5 and 2 h after dosing (median 1 h). Its elimination was almost complete within 6 h. Peak plasma levels of benazeprilat, the active metabolite of benazepril, were observed between 1 and 6 h (median 2.5 h). The elimination of benazeprilat from plasma was biphasic, with mean initial and terminal half-lives of 3.0 and 17.3 h, respectively. On average, the pharmacokinetic parameters of benazepril and benazeprilat in the patients did not differ from those in a historical control group of healthy volunteers, but intersubject variability in the AUC and half-lives of benazeprilat was greater in the patients. Plasma ACE was completely inhibited from 1.5 to 6 h after dosing, and at 48 h the mean inhibition was still 42%. Plasma renin showed substantial intersubject variation. Mean supine blood pressure (systolic/diastolic) was reduced from baseline by a maximum of 18/13 mm Hg at 6 h. Proteinuria was diminished after benazepril in 7 patients. In conclusion, the results of this study suggest that proteinuria in the nephrotic range does not require a change in benazepril dosage.

Effects of the single and repeated administration of benazepril on systemic and forearm circulation and cardiac function in hypertensive patients

The hemodynamic and cardiac effects of the new angiotensin-converting enzyme inhibitor, benazepril, were studied in 28 hypertensives in a double blind, placebo-controlled, between-patient study. Hemodynamic studies were performed noninvasively by means of M-mode echo (central hemodynamics and left ventricular systolic function), 2-D echo-Doppler (left ventricular diastolic function), and pulsed Doppler flowmetry (forearm circulation). Examinations were done at the end of a placebo run-in period and 3 hours after benazepril administration, both on the first day and after 6 weeks of treatment (10 or 20 mg once daily, according to patient response). In comparison with placebo, benazepril reduced systolic (p = 0.04) and diastolic (p = 0.003) blood pressure, because of a significant reduction in systemic vascular resistance (p = 0.03), while cardiac output was unchanged. Forearm vascular resistance was reduced and brachial artery compliance increased, although not to a statistically significant level (both p = 0.07). Both systolic and diastolic left ventricular function were positively influenced by the afterload reduction: End-systolic stress was reduced by 12% (p = 0.07), as was the late diastolic peak flow velocity (p = 0.02). All hemodynamic changes were evident after acute benazepril administration, and no differences was observed between acute and repeated treatment. We conclude that, similar to other ACE-inhibitors, benazepril reduces blood pressure through a reduction in vascular resistance, while cardiac output and heart rate are unaffected. These hemodynamic effects occur as early as after the first administration and exert a favorable influence on left ventricular dynamics.

Clinical pharmacokinetics of angiotensin converting enzyme (ACE) inhibitors in renal failure

Arterial hypertension occurs frequently in patients with chronic renal failure. Antihypertensive treatment of arterial hypertension with angiotensin converting enzyme (ACE) inhibitors has been shown to be effective with a low incidence of adverse effects compared with other drug classes. Furthermore, treatment with ACE inhibitors may slow the progression of renal function impairment in certain groups of patients, such as those with diabetes. Most ACE inhibitors are prodrugs which are converted by hepatic esterolysis to an active diacid metabolite. Only captopril and lisinopril have sufficient oral bioavailability and are given as active drugs. ACE inhibitors can be subdivided into 3 classes with regard to the active group: the majority of ACE inhibitors are carboxyl-containing drugs, a new class of ACE inhibitors possess a phosphoryl-group and captopril and related compounds are sulfhydryl-containing drugs. The predominant elimination pathway of ACE inhibitors is excretion via the kidneys. Therefore, renal insufficiency is associated with reduced elimination of most ACE inhibitors and, thus, altered pharmacokinetic properties. This is most evident in chronic renal failure when glomerular filtration rates (GFR) are < 30 to 40 ml/min (1.8 to 2.4 L/h). As renal clearance decreases, the peak plasma concentration and area under the plasma concentration-time curve of the active drugs or diacids are increased and time to peak concentrations and half-life are prolonged. However, there are large between-drug differences in the changes in pharmacokinetic parameters, resulting in different degrees of drug accumulation after consecutive administration. This leads, for example, to high accumulation rates for drugs such as lisinopril, or cilazaprilat. In contrast, fosinopril, which is also excreted to a large extent by the hepatobiliary pathway, does not seem to accumulate in renal failure. In general, pharmacokinetics and conversion of prodrugs seem to be slightly affected in chronic renal failure; however, these changes do not appear to be clinically relevant. Efficiency of clearance for prodrugs or active drugs and their respective metabolites by haemodialysis or peritoneal dialysis varies considerably. For some ACE inhibitors, such as captopril or enalapril, the high elimination fraction by haemodialysis necessitates a supplemental dose after dialysis. Other ACE inhibitors, such as quinapril or cilazapril, are only poorly eliminated by haemodialysis or peritoneal dialysis. Dosage recommendations for treatment with ACE inhibitors in chronic renal failure depend on the specific pharmacokinetic properties of the various agents. For most ACE inhibitors, dosage adjustment is recommended in moderate and severe impairment of renal function, with resultant dosages being 25 to 50% of those recommended for patients with normal renal function.

The pharmacokinetics of benazepril relative to other ACE inhibitors

Benazepril is a prodrug that, following rapid conversion to benazeprilat, is a potent nonsulfhydryl inhibitor of angiotensin-converting enzyme. The absorption, bioactivation, distribution, and elimination of benazepril and benazeprilat have been evaluated in healthy subjects, hypertensive patients, and patients with characteristics known to alter the pharmacokinetic disposition of ACE inhibitors, such as renal impairment, hepatic impairment, and advanced age. Following oral administration, benazepril is absorbed and transformed into benazeprilat in the liver. Coadministration of benazepril with food delays absorption slightly but does not affect the ultimate bioavailability of benazeprilat. Severe hepatic impairment slows conversion of benazepril to benazeprilat but does not affect the overall bioavailability of benazeprilat; thus dosage adjustment is not necessary in the hepatically impaired population. Mild-to-moderate renal impairment (creatinine clearance greater than 30 ml/min) slightly increases benazeprilat concentrations; severe renal impairment (creatinine clearance less than 30 ml/min) reduces benazeprilat elimination and requires dosage reduction. In elderly patients, benazepril disposition is the same as in younger patients, although benazeprilat clearance is slightly reduced. No clinically significant drug-drug interactions occur with benazepril and many other medications commonly prescribed to elderly hypertensive patients. The pharmacokinetic characteristics of benazepril are stable over a wide range of conditions, and dosage adjustments for pharmacokinetic reasons are required infrequently.

Pharmacokinetics of newer drugs in patients with renal impairment (Part II)

Cardiovascular diseases occur frequently in patients with renal failure. Any pharmacokinetic impairment in these diseases should be considered when individualizing drug therapy. The pharmacokinetics of new cardiovascular drugs in uraemic patients are reviewed: alpha- and beta-blocking agents, ACE inhibitors, centrally acting antihypertensive agents, calcium antagonists, antiarrhythmic agents and inotropic agents. Guidelines are proposed for adjustment of dosage regimens as a function of renal impairment. Renal or extrarenal elimination of drugs and their metabolites, and the activity of the latter, are taken into account. The disposition of new drugs such as flestolol, alacepril, delapril, propafenone, milrinone or enoximone, is not well documented in patients with renal failure. Further characterizations of the elimination of these compounds are needed and the potential therapeutic or toxic effects of the metabolites require evaluation to determine whether the dosage needs to be adjusted. Until such investigations are performed, those drugs should not be used in uraemic patients; if no therapeutic alternative is available, clinical controls are necessary at regular intervals. Relationships between pharmacological or therapeutic effects and drug plasma concentrations should be evaluated for such long term use drugs. The knowledge of a plasma concentration therapeutic window is important to provide information which will be useful in determining appropriate drug dosage in renal failure.

The disposition of [14C]-labelled benazepril HCl in normal adult volunteers after single and repeated oral dose

1. The disposition of [14C]-labelled benazepril HCl, an ACE-inhibitor, was studied in four normal adult volunteers after a single oral dose of 20 mg and after repeated doses of 20 mg once daily for 5 days. Radioactivity was measured in plasma, urine and faeces. The prodrug ester benazepril and the pharmacologically active metabolite benazeprilat were determined quantitatively in plasma and urine by a g.c.-m.s. method. The pattern of metabolites in urine was analysed semiquantitatively by h.p.l.c.-radiometry. 2. After a single oral dose at least 37% was absorbed, as indicated by urinary recovery. The peak plasma concentration of benazepril (0.58 +/- 0.13 nmol/g (SD] was observed at 0.5h after dose, indicating rapid absorption. Peak concentrations of radioactivity (1.88 +/- 0.48 nmol/g) and of active benazeprilat (0.84 +/- 0.25 nmol/g) were observed at 1 h after dose, demonstrating rapid bioactivation. 3. The area under the plasma curve (AUC0-96 h) of total radioactivity amounted to 9.7 +/- 1.1 (nmol/g)h, 5% of which was accounted for by benazepril and about 50% by benazeprilat. 4. Over 9 days 96.8 +/- 0.5% of the dose was excreted in urine and faeces. Urinary excretion accounted for 37.0 +/- 6.0% of the dose, 80% of which was recovered in the first 8 h after dosing. 5. In urine, only 0.4% of the dose (1% of the radioactivity) was excreted as unchanged benazepril, indicating that the compound was extensively metabolized. Benazeprilat accounted for 17% of the dose (about half of the radioactivity; 0-96 h). Glucuronide conjugates of benazepril and benazeprilat constituting approximately 11% and 22% of the radioactivity (about 4% and 8% of the dose; 0-48 h) were tentatively identified. 6. Repeated oral treatment with benazepril HCl did not influence the pharmacologically relevant kinetics and disposition parameters.

The influence of hepatic cirrhosis on the pharmacokinetics of benazepril hydrochloride

The influence of hepatic disease on the pharmacokinetics of the new ACE inhibitor, benazepril hydrochloride, was evaluated in 12 male patients suffering from liver cirrhosis. The patients received a single oral 20 mg dose. The plasma concentrations and urinary excretion of unchanged benazepril and its active metabolite benazeprilat were determined. Compared with a historical control group of healthy volunteers treated with the same benazepril. HC1 dose, the plasma concentrations of benazepril were doubled in the cirrhotic patients. However, the time to reach maximum concentration (0.5 h) was not affected. The plasma kinetics and the urinary excretion of the metabolite benazeprilat were not significantly altered: Area under the curve and maximum concentration as well as time to maximum concentration (1.5 h) were comparable with those in the healthy subjects. There was also no significant difference between the two populations for the total urinary excretion and the renal clearance of benazeprilat. Both benazepril and benazeprilat were highly bound to serum proteins (96 and 94 per cent, respectively). In conclusion, the rate and the amount of bioactivation of the inactive prodrug benazepril to the active benazeprilat were virtually unaffected by hepatic cirrhosis. Thus, there seems to be no need for dosage adjustment of benazepril hydrochloride in patients suffering from cirrhosis of the liver.

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)

Pharmacokinetics and pharmacodynamics of the ace inhibitor benazepril hydrochloride in the elderly

The pharmacokinetics and pharmacodynamics of a single oral dose benazepril.HCl 10 mg have been studied in 15 healthy volunteers aged 65 to 80 y. The kinetics of unchanged benazepril and its active metabolite benazeprilat did not differ significantly in males and females, so the combined kinetic data from all 15 elderly subjects were compared with a historical control group of 19-32 year-old healthy men treated in the same way. The disposition of benazepril was not affected by age. The time to maximum plasma concentration, tmax (0.5 h) and elimination half-life (0.6 h) in the elderly were the same as in young subjects. The kinetics of benazeprilat was slightly changed in the elderly; although its tmax (1.5 h) was not affected, Cmax and the AUC were 20-40% greater. The elimination half-life of benazeprilat during the first 24 h after dosing in the elderly was increased by about 20% to 3.2 h. The renal plasma clearance of benazeprilat (18.1 ml.min-1) was about 20% smaller than in the young subjects. An average of 18.5% of the dose was recovered as benazeprilat in the 24 h urine from the elderly subjects, which was similar to the recovery in the young subjects. Both benazepril and benazeprilat were highly bound to serum proteins (96 and 95%, respectively). Mean systolic and diastolic blood pressures in the elderly were reduced by a maximum of 37/16 mm Hg at 6 h, in association with a small rise in pulse rate. Treatment was generally well tolerated.(ABSTRACT TRUNCATED AT 250 WORDS)