Efficacy of monotherapy with benazepril, an angiotensin converting enzyme inhibitor, in dogs with naturally acquired chronic mitral insufficiency

Management of Chronic Congestive Heart Failure Caused by Myxomatous Mitral Valve Disease in Dogs: A Narrative Review from 1970 to 2020

Simple Summary

Myxomatous mitral valve disease (MMVD) is the most common acquired cardiovascular disease in dogs. The progression of the disease and the increasing severity of valvular regurgitation cause a volume overload of the left heart, leading to left atrial and ventricular remodeling and congestive heart failure (CHF). The treatment of chronic CHF secondary to MMVD in dogs has not always been the same over time. In the last fifty years, the drugs utilized have considerably changed, as well as the therapeutic protocols. Some drugs have also changed their intended use. An analysis of the literature concerning the therapy of chronic heart failure in dogs affected by this widespread degenerative disease is not available; a synthesis of the published literature on this topic and a description of its current state of art are needed. To the authors’ knowledge, a review of this topic has never been published in veterinary medicine; therefore, the aim of this study is to overview the treatments of chronic CHF secondary to MMVD in dogs from 1970 to 2020 using the general framework of narrative reviews.

Abstract

The treatment of chronic congestive heart failure (CHF), secondary to myxomatous mitral valve disease (MMVD) in dogs, has considerably changed in the last fifty years. An analysis of the literature concerning the therapy of chronic CHF in dogs affected by MMVD is not available, and it is needed. Narrative reviews (NRs) are aimed at identifying and summarizing what has been previously published, avoiding duplications, and seeking new study areas that have not yet been addressed. The most accessible open-access databases, PubMed, Embase, and Google Scholar, were chosen, and the searching time frame was set in five decades, from 1970 to 2020. The 384 selected studies were classified into categories depending on the aim of the study, the population target, the pathogenesis of MMVD (natural/induced), and the resulting CHF. Over the years, the types of studies have increased considerably in veterinary medicine. In particular, there have been 43 (24.29%) clinical trials, 41 (23.16%) randomized controlled trials, 10 (5.65%) cross-over trials, 40 (22.60%) reviews, 5 (2.82%) comparative studies, 17 (9.60%) case-control studies, 2 (1.13%) cohort studies, 2 (1.13%) experimental studies, 2 (1.13%) questionnaires, 6 (3.40%) case-reports, 7 (3.95%) retrospective studies, and 2 (1.13%) guidelines. The experimental studies on dogs with an induced form of the disease were less numerous (49–27.68%) than the studies on dogs affected by spontaneous MMVD (128–72.32%). The therapy of chronic CHF in dogs has considerably changed in the last fifty years: in the last century, some of the currently prescribed drugs did not exist yet, while others had different indications.

Angiotensin-converting enzyme inhibitors in preclinical myxomatous mitral valve disease in dogs: systematic review and meta-analysis

To determine the efficacy and adverse events of the administration of angiotensin-converting enzyme inhibitors for the management of preclinical myxomatous mitral valve disease in dogs. A comprehensive search using Pubmed/MEDLINE, LILACS and CAB abstracts databases was performed. Randomised clinical trials that assessed efficacy and adverse events of angiotensin-converting enzyme inhibitors for the management of preclinical myxomatous mitral valve disease in dogs were included. Certainty of evidence was rated using GRADE methods. Four randomised clinical trials were included. While safe, angiotensin-converting enzyme inhibitors administration to dogs with myxomatous mitral valve disease and cardiomegaly results in little to no difference in the risk of development congestive heart failure (high certainty of evidence; relative risk: 1.03; 95% confidence interval: 0.87 to 1.23) and may result in little to no difference in cardiovascular-related (low certainty of evidence; relative risk: 1.01; 95% confidence interval: 0.54 to 1.89) and all-cause mortality (low certainty of evidence; relative risk: 0.93; 95% confidence interval: 0.63 to 1.36). Administration of angiotensin-converting enzyme inhibitors to dogs with myxomatous mitral valve disease without cardiomegaly may result in a reduced risk of congestive heart failure development. However, the range in which the actual effect for this outcome may be, the "margin of error," indicates it might also increase the risk of congestive heart failure development (low certainty of evidence; relative risk: 0.86; 95% confidence interval: 0.54 to 1.35). Administration of angiotensin-converting enzyme inhibitors to dogs with preclinical myxomatous mitral valve disease and cardiomegaly results in little to no difference in the risk of the development of congestive heart failure and may result in little to no difference in cardiovascular-related and all-cause mortality. The certainty of evidence of the efficacy of angiotensin-converting enzyme inhibitors administration to dogs without cardiomegaly was low.

Correction of serum chloride concentration in dogs with congestive heart failure

Background

Hypochloremia associated with congestive heart failure (CHF) in dogs is likely multifactorial. Loop diuretics cause 1:2 sodium [Na⁺]:chloride [Cl⁻] loss, whereas water retention causes a 1:1 [Na⁺]:[Cl⁻] dilution. Mathematical [Cl⁻] correction separates these effects on [Cl⁻].

Hypothesis

We hypothesized that corrected [Cl⁻] (c[Cl⁻]) would not differ from measured [Cl⁻] (m[Cl⁻]) in dogs with controlled CHF because of loop diuretics, and dogs with refractory CHF would have higher c[Cl⁻] than m[Cl⁻], indicating relative water excess.

Animals

Seventy‐one client‐owned dogs with acquired heart disease, without CHF (NO‐CHF), 76 with Stage C CHF and 24 with Stage D CHF.

Methods

Clinicopathological data from a previous study were retrospectively analyzed. Corrected [Cl⁻], m[Cl⁻], and differences were compared among NO‐CHF, Stage C CHF, and Stage D CHF, using the formula: c[Cl⁻] = (mid‐reference range [Na⁺]/measured [Na⁺]) × m[Cl⁻].

Results

Corrected [Cl⁻] and m[Cl⁻] were lower in Stage D vs Stage C and NO‐CHF (all P < .0001). The c[Cl⁻] was higher than m[Cl⁻] in Stage D (P < .0001) but not Stage C or NO‐CHF. Median difference between c[Cl⁻] and m[Cl⁻] was higher for Stage D vs Stage C (P = .0003). No hypochloremic Stage D dogs had normal c[Cl⁻], but 11/24 had [Cl⁻] that was increased by >2 mmol/L.

Conclusions and Clinical Importance

Serum [Cl⁻] increased after mathematical correction in Stage D CHF dogs but not in Stage C and NO‐CHF dogs. Although c[Cl⁻] was higher than m[Cl⁻] in Stage D dogs supportive of relative water excess, hypochloremia persisted, consistent with concurrent loop diuretic effects on electrolytes. Future study correlating c[Cl⁻] to antidiuretic hormone concentrations is warranted.

The effect of enalapril on furosemide-activated renin-angiotensin-aldosterone system in healthy dogs

Studies in our laboratory have revealed that furosemide-induced RAAS activation, evaluated via the urine aldosterone-to-creatinine ratio (UAldo:C), was not attenuated by the coadministration of benazepril, while enalapril successfully suppressed amlodipine-induced urinary aldosterone excretion. This study was designed to evaluate the efficacy of enalapril in suppressing ACE activity and furosemide-induced circulating RAAS activation. Failure to do so would suggest that this failure may be a drug class effect. We hypothesized that enalapril would suppress ACE activity and furosemide-induced circulating RAAS activation. Sixteen healthy hound dogs. The effect of furosemide (2 mg/kg PO, q12 h; Group F) and furosemide plus enalapril (0.5 mg/kg PO, q12 h; Group FE) on circulating RAAS was determined by plasma ACE activity, 4-6 h post-treatment, and urinary A:C on days -1, -2, 1, 4, and 7. There was a significant increase in the average urine aldosterone-to-creatinine ratio (UAldo:C) after administration of furosemide (P < 0.05). Enalapril inhibited ACE activity (P < 0.0001) but did not significantly reduce aldosterone excretion. A significant (P < 0.05) increase in the UAldo:C was maintained for the 7 days of the study in both groups. Enalapril decreased plasma ACE activity; however, it did not suppress furosemide-induced RAAS activation, as determined by the UAldo:C. While enalapril blunts ACE activity, the absence of circulating RAAS suppression may be due to angiotensin II reactivation, alternative RAAS pathways, and furosemide overriding concurrent ACE inhibition, all indicating the existence of aldosterone breakthrough (ABT). Along with similar findings with benazepril, it appears that failure to suppress aldosterone suppression with furosemide stimulation may be a drug class effect. The discrepancy between the current data and the documented benefits of enalapril likely reflects the efficacy of this ACE inhibitor in suppressing tissue RAAS, variable population responsiveness to ACE-inhibition, and/or providing additional survival benefits, possibly through as yet unknown mechanisms.

Aldosterone breakthrough with benazepril in furosemide-activated renin-angiotensin-aldosterone system in normal dogs

Pilot studies in our laboratory revealed that furosemide-induced renin-angiotensin-aldosterone system (RAAS) activation was not attenuated by the subsequent co-administration of benazepril. This study was designed to evaluate the effect of benazepril on angiotensin-converting enzyme (ACE) activity and furosemide-induced circulating RAAS activation. Our hypothesis was that benazepril suppression of ACE activity would not suppress furosemide-induced circulating RAAS activation, indicated by urinary aldosterone concentration. Ten healthy hound dogs were used in this study. The effect of furosemide (2 mg/kg p.o., q12h; Group F; n = 5) and furosemide plus benazepril (1 mg/kg p.o., q24h; Group FB; n = 5) on circulating RAAS was determined by plasma ACE activity, 4-6 h posttreatment, and urinary aldosterone to creatinine ratio (UAldo:C) on days -1, -2, 1, 3, and 7. There was a significant increase in the average UAldo:C (μg/g) after the administration of furosemide (Group F baseline [average of days -1 and -2] UAldo:C = 0.41, SD 0.15; day 1 UAldo:C = 1.1, SD 0.56; day 3 UAldo:C = 0.85, SD 0.50; day 7 UAldo:C = 1.1, SD 0.80, P < 0.05). Benazepril suppressed ACE activity (U/L) in Group FB (Group FB baseline ACE = 16.4, SD 4.2; day 1 ACE = 3.5, SD 1.4; day 3 ACE = 1.6, SD 1.3; day 7 ACE = 1.4, SD 1.4, P < 0.05) but did not significantly reduce aldosterone excretion (Group FB baseline UAldo:C = 0.35, SD 0.16; day 1 UAldo:C = 0.79, SD 0.39; day 3 UAldo:C 0.92, SD 0.48, day 7 UAldo:C = 0.99, SD 0.48, P < 0.05). Benazepril decreased plasma ACE activity but did not prevent furosemide-induced RAAS activation, indicating aldosterone breakthrough (escape). This is particularly noteworthy in that breakthrough is observed at the time of initiation of RAAS suppression, as opposed to developing after months of therapy.

The influence of enalapril and spironolactone on electrolyte concentrations in Doberman pinschers with dilated cardiomyopathy

The combination of an angiotensin-converting enzyme inhibitor (ACEI) with an aldosterone receptor antagonist can increase serum potassium and magnesium and lower serum sodium concentrations. The objective of this study was to retrospectively determine whether an ACEI and spironolactone can be co-administered to Doberman pinschers with occult dilated cardiomyopathy without serious adverse influences on serum electrolyte concentrations. Between 2001 and 2007, 26 client-owned Doberman pinschers were given enalapril, spironolactone, and carvedilol and followed for at least 6 months. Most dogs had been prescribed mexiletine for ventricular tachyarrhythmia suppression. Dogs were treated with pimobendan when congestive heart failure was imminent. Baseline and follow-up (3-10 visits) color-flow Doppler echocardiograms, serum urea nitrogen (SUN), creatinine, sodium, potassium, and magnesium concentration data were tabulated. Compared to baseline data, there were no significant changes in serum sodium or serum creatinine concentrations. Serum magnesium (P = 0.003), serum potassium (P = 0.0001), and SUN (P = 0.0001) concentrations increased significantly with time. Although the combination of ACEI and spironolactone was associated with significant increases in magnesium, potassium, and SUN concentrations, these changes were of no apparent clinical relevance. At the dosages used in this study, this combination of drugs appears safe.

The effect of benazepril on survival times and clinical signs of dogs with congestive heart failure: Results of a multicenter, prospective, randomized, double-blinded, placebo-controlled, long-term clinical trial

OBJECTIVE

To test the efficacy and tolerability of long-term administration of the angiotensin converting enzyme inhibitor, benazepril, in dogs with heart failure.

METHODS

The study was a prospective, randomized, double-blind, placebo-controlled clinical trial involving 16 centers in France, Italy, Switzerland and UK. A total of 162 dogs with class II and III (ISACHC classification) heart failure caused by chronic valvular disease (CVD) or dilated cardiomyopathy (DCM) were enrolled. Benazepril (minimum dosage, 0.25 mg/kg) or placebo were administered orally once daily for up to 34 months, either alone or as add-on therapy to "standard therapy" i.e. diuretics and/or digoxin and/or anti-arrhythmic drugs.

RESULTS

The mean survival time (to death or withdrawal from the study due to worsening of heart failure) was 2.7 times longer in the benazepril treated group (428 days) as compared with the placebo group (158 days). Differences reached statistical significance (p<0.05 Cox proportional hazards model, 44% reduction in risk). The survival rate after one year was 49% with benazepril and 20% with placebo. Benazepril produced a statistically significant (p<0.05) reduction (by 46%) in the risk of worsening of heart failure (to ISACHC class III) when therapy was initiated early (in ISACHC class II). In sub-group analyses, a statistically significant (p<0.05) benefit of benazepril was reached for both survival and worsening endpoints for dogs with CVD (n=125), but not for the small sample of dogs with DCM (37). Benazepril also improved the exercise tolerance and global clinical condition at day 28 (p<0.05). As compared to the placebo group, dogs treated with benazepril presented with the same frequency of undesirable clinical events and fewer biochemical disturbances (less frequent increases in plasma urea or creatinine and decreases in plasma potassium).

CONCLUSIONS

Benazepril extended the useful life-span of dogs with ISACHC class II and III heart failure (due to CVD) and was well tolerated.

Development and evaluation of a questionnaire for assessment of health-related quality of life in cats with cardiac disease

OBJECTIVE

To develop, validate, and evaluate a questionnaire (Cats' Assessment Tool for Cardiac Health [CATCH] questionnaire) for assessing health-related quality of life in cats with cardiac disease.

DESIGN

Prospective study.

ANIMALS

275 cats with cardiac disease.

PROCEDURES

The questionnaire was developed on the basis of clinical signs of cardiac disease in cats. A CATCH score was calculated by summing responses to questionnaire items; possible scores ranged from 0 to 80. For questionnaire validation, owners of 75 cats were asked to complete the questionnaire (10 owners completed the questionnaire twice). Disease severity was assessed with the International Small Animal Cardiac Health Council (ISACHC) classification for cardiac disease. Following validation, the final questionnaire was administered to owners of the remaining 200 cats.

RESULTS

Internal consistency of the questionnaire was good, and the CATCH score was significantly correlated with ISACHC classification. For owners that completed the questionnaire twice, scores were significantly correlated. During the second phase of the study, the CATCH score ranged from 0 to 74 (median, 7) and was significantly correlated with ISACHC classification.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that the CATCH questionnaire is a valid and reliable method for assessing health-related quality of life in cats with cardiac disease. Further research is warranted to test the tool's sensitivity to changes in medical treatment and its potential role as a clinical and research tool.

Clinical evaluation of imidapril in congestive heart failure in dogs: results of the EFFIC study

OBJECTIVES

The clinical efficacy and safety of imidapril were evaluated in dogs that presented with mild to severe congestive heart failure (New York Heart Association stage II to IV) by comparing the success rate of imidapril with a positive control by a non-inferiority approach.

METHODS

This good, clinical practice compliant, multicentre study (EFFIC study) enrolled 142 client-owned dogs and was conducted in 20 locations in France, Belgium and Germany. Dogs of various breed, age and weight were included in the study. These dogs were randomised into two groups that were treated for 84 days with either the test product, imidapril, or the positive control, benazepril, and followed up in parallel over this period. Both treatments were administered at a dose of 0.25 mg/kg once a day with the possibility of doubling this dose to 0.5 mg/kg if considered necessary from a clinical point of view. In addition, concomitant treatment was given to dogs presenting with pulmonary oedema and/or ascites, supraventricular tachyarrhythmia and/or dilated cardiomyopathy. The evolution of the New York Heart Association stage and the "functional signs" score were evaluated as primary efficacy criteria.

RESULTS

The success rate in the imidapril group was 66 compared with 68 per cent in the benazepril group. Regarding safety, 35 dogs in each group experienced at least one adverse event. Nine dogs in each group experienced at least one serious adverse event. The difference between these results was not statistically significant.

CLINICAL SIGNIFICANCE

Imidapril is as efficacious and safe as the reference product, benazepril.

Tratamento de insuficiência cardíaca com benazepril em cães com cardiomiopatia dilatada e endocardiose

Foram avaliados os efeitos clínicos do benazepril, um inibidor da enzima de conversão da angiotensina de ação prolongada, em cães com insuficiência cardíaca congestiva (ICC) secundária à endocardiose de mitral ou cardiomiopatia dilatada. O medicamento foi administrado na dose de 0,25 a 0,5mg/kg/dia. Diuréticos, digitálicos e fármacos antiarrítmicos foram usados de acordo com a necessidade de cada paciente. Exames físico, radiográfico e eletrocardiográfico foram realizados nos dias 0, 7, 28 e 56. A gasometria arterial e a bioquímica sérica foram avaliadas nos dias 0 e 56. Os sinais de dispnéia e o estado geral dos pacientes melhoraram em todos os cães após o início do tratamento. Houve diminuição na freqüência da tosse e não houve alterações no eletrocardiograma, exceto pela diminuição na amplitude e na duração da onda P. Nenhum efeito colateral foi observado. Conclui-se que o benazepril é um inibidor da enzima de conversão da angiotensina, eficaz e bem tolerado no tratamento da ICC no cão.

Development and evaluation of a questionnaire for assessing health-related quality of life in dogs with cardiac disease

OBJECTIVE

To develop and evaluate a questionnaire (functional evaluation of cardiac health [FETCH] questionnaire) for assessing health-related quality of life in dogs with cardiac disease.

DESIGN

Prospective study.

ANIMALS

360 dogs with cardiac disease

PROCEDURE

The questionnaire was developed on the basis of widely accepted clinical signs of cardiac disease in dogs. A FETCH score was calculated by summing responses to questionnaire items; possible scores ranged from 0 to 85. For questionnaire validation, owners of 60 dogs were asked to complete the questionnaire and provide an overall assessment of their dogs' quality of life (16 owners completed the questionnaire twice). Disease severity was assessed with the International Small Animal Cardiac Health Council (ISACHC) classification for cardiac disease. Following validation, the final questionnaire was administered to owners of the remaining 300 dogs.

RESULTS

Internal consistency of the questionnaire was good, and the FETCH score was significantly correlated with the owner-reported quality-of-life score and with ISACHC classification. For owners that completed the questionnaire twice, scores were significantly correlated. During the second phase of the study, the FETCH score ranged from 0 to 70 (median, 7) and was significantly correlated with ISACHC classification, but did not vary significantly with underlying disease. For dogs examined twice, the change in FETCH score was significantly greater for dogs in which ISACHC classification improved than for dogs in which ISACHC classification was unchanged.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that the FETCH questionnaire is a valid and reliable method for assessing health-related quality of life in dogs with cardiac disease.

Angiotensin-converting enzyme inhibitors in the therapy of renal diseases

Renal diseases, especially chronic renal failure (CRF), are common in canine and feline medicine. The renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in these conditions in the development of renal lesions and the progression of kidney dysfunction. Angiotensin-converting enzyme inhibitors (ACEI) are currently considered as the most efficient agents in therapeutic strategies. The benefit of an ACEI treatment can be explained by at least three mechanisms: ACEI limit systemic and glomerular capillary hypertension, have an antiproteinuric effect, and retard the development of glomerulosclerosis and tubulointerstitial lesions. These effects have been studied in dogs and cats, and there is now some evidence to support the recommendation of ACEI therapy in dogs and cats with CRF. Nevertheless the prescription of ACEI in such patients should take into account the potential influence of renal impairment on ACEI disposition, and adverse effects on the renal function itself (especially hypotension and acute reductions in glomerular filtration rate). The risk of drug interaction with diuretics, nonsteroidal anti-inflammatory drugs and anesthetics, should not be overestimated. Furthermore, hypotension may occur in patients on a low sodium diet.

Creatinine in the Dog: A Review

Creatinine is the analyte most frequently measured in human and veterinary clinical chemistry laboratories as an indirect measure of glomerular filtration rate (GFR). Although creatinine metabolism and the difficulties of creatinine measurement have been reviewed in human medicine, similar reviews are lacking in veterinary medicine. The aim of this review is to summarize information and data about creatinine metabolism, measurement, and diagnostic significance in the dog. Plasma creatinine originates from the degradation of creatine and creatine phosphate, which are present mainly in muscle and in food. Creatinine is cleared by glomerular filtration with negligible renal secretion and extrarenal metabolism, and its clearance is a good estimate of GFR. Plasma and urine creatinine measurements are based on the nonspecific Jaffé reaction or specific enzymatic reactions; lack of assay accuracy precludes proper interlaboratory comparison of results. Preanalytical factors such as age and breed can have an impact on plasma creatinine (P-creatinine) concentration, while many intraindividual factors of variation have little effect. Dehydration and drugs mainly affect P-creatinine concentration in dogs by decreasing GFR. P-creatinine is increased in renal failure, whatever its cause, and correlates with a decrease in GFR according to a curvilinear relationship, such that P-creatinine is insensitive for detecting moderate decreases of GFR or for monitoring progression of GFR in dogs with severely reduced kidney function. Low sensitivity can be obviated by determining endogenous or exogenous clearance rates of creatinine. A technique for determining plasma clearance following IV bolus injection of exogenous creatinine and subsequent serial measurement of P-creatinine does not require urine collection and with additional studies may become an established technique for creatinine clearance in dogs.

An angiotensin converting enzyme inhibitor, benazepril can be transformed to an active metabolite, benazeprilat, by the liver of dogs with ascitic pulmonary heartworm disease

To examine whether an angiotensin converting enzyme (ACE) inhibitor, benazepril, can be transformed to the active metabolite, benazeprilat, by severely injured liver of dogs with ascitic heartworm disease, benazepril hydrochloride was administered orally to dogs once daily for 7 consecutive days at a dose rate of 0.29 mg/kg to 0.63 mg/kg of body weight, and plasma benazepril and benazeprilat concentrations were determined on the 1st and 7th administration days. In 7 dogs with ascitic pulmonary heartworm disease, plasma benazeprilat concentrations tended to be higher than in 7 control dogs both on the 1st and 7th administration days. The peak concentration and area under the concentration-time curve tended to be greater in dogs of the ascites group than in control dogs, but the statistics could not detect significant differences in the time to peak concentration and t(1/2) between the control and ascites groups. Plasma ACE activities decreased after administration of benazepril. In dogs with ascitic heartworm disease, benazepril was readily transformed to benazeprilat by the liver, and was effective for suppression of plasma ACE activity.

Treatment of congestive heart failure a neuroendocrine disorder

The understanding of heart failure is no longer based on a supply and demand model of pump failure. Rather, heart failure is seen as a complex pathophysiological process with activation of various neuroendocrine systems. The goals of treatment have changed towards modifying these counterproductive neuroendocrine systems and slowing myocardial maladaptation. Angiotensin converting enzyme inhibitors are the only licensed drugs in veterinary practice that have a direct effect on neurohormones in heart failure. The range of drug options in human medicine is greater and some of these drugs are also increasingly being used in veterinary cardiology practice. This review describes the neuroendocrine systems involved in heart failure and discusses the range of drugs available in human and veterinary medicine. In doing so, it concentrates on the evidence available from good quality randomised trials in both the veterinary field and, where relevant, the human medical field.

Spectral analysis of heart rate variability in dogs with mild mitral regurgitation

OBJECTIVE

To assess autonomic function in dogs with mild mitral regurgitation (MR) that did not have clinical signs of the condition.

ANIMALS

6 healthy adult Beagles.

PROCEDURE

Mild MR was experimentally induced. A 24-hour ambulatory ECG was recorded before and after induction of MR. Heart rate variability was analyzed in frequency domains by use of the ambulatory ECG. Low-frequency (LF) and high-frequency (HF) power were calculated by integrating over their frequency intervals, and the ratio of LF to HF was also calculated. Measurements of frequency domains were analyzed for 4 time periods (midnight to 6 AM, 6 AM to noon, noon to 6 PM, and 6 PM to midnight).

RESULTS

Dogs with experimentally induced MR were classified as International Small Animal Cardiac Health Council class Ia. The HF power of dogs with MR was significantly decreased between 6 AM and noon. The ratio of LF to HF in dogs with MR was significantly increased for the periods between midnight and 6 AM, 6 AM and noon, and noon and 6 PM.

CONCLUSIONS AND CLINICAL RELEVANCE

Compensatory response through autonomic modulation was observed in dogs with mild MR that did not have abnormalities, except for cardiac murmur, during clinical examination. This result suggests that treatment during the early stages of mild MR may be beneficial. Additional studies are necessary to determine whether such treatment will delay the onset of congestive heart failure and prolong survival in dogs affected with mild MR.

Plasma concentrations of an angiotensin-converting enzyme inhibitor, benazepril, and its active metabolite, benazeprilat, after repeated administrations of benazepril in dogs with experimental kidney impairment

In order to examine the safety of an angiotensin-converting enzyme (ACE) inhibitor in dogs with impaired renal excretion route, benazepril was administered orally, and plasma concentrations of benazeprilat, the active metabolite of benazepril, were determined in dogs with renal mass reduction (1/4th kidney) created by right-side nephrectomy and ligation of branches of the left renal arteries. Five dogs were administered benazepril orally at a given dose (0.5 mg/kg body weight) and 4 other dogs received 20 times that dose (10 mg/kg body weight) once daily for 15 consecutive days before (intact kidney period) and after (1/4th kidney period) creation of kidney impairment. Six control dogs received surgical treatment, but no drug. After creating a 1/4th kidney, plasma urea nitrogen and creatinine concentrations increased to approximately 30 mg/dl and 2.0 mg/dl, respectively, and renal plasma flow and glomerular filtration rate decreased to 37% and 30% of pre-treatment values, respectively. However, these parameters did not change significantly during the 1/4th kidney period both in the 0.5 mg/kg and 10 mg/kg groups. In the 0.5 mg/kg group, plasma benazeprilat concentrations increased to approximately 20 ng/ml to 340 ng/ml 2 hr after each administration, and there were no significant differences between the plasma benazeprilat concentrations during the intact and 1/4th kidney periods. In the 10 mg/kg group, plasma benazeprilat concentrations varied in the individual dog, but did not increase with the days of administration, and were not significantly different on each administration day between the intact and 1/4th kidney periods in either dose group. The AUCs(0-24) of plasma benazeprilat concentrations determined on the 15th administration day were not different between the intact and 1/4th kidney periods in dogs of either dose group. Plasma ACE activities decreased after drug administration in dogs of both groups. Benazepril seemed to have a high safety, and the adjustment of dosage regimen might not be needed in dogs with mild to moderate renal function impairment because the drug was excreted both from the kidneys and liver.