Single-dose pharmacokinetics and cardiovascular effects of oral pimobendan in healthy cats

A pilot study of the proarrhythmic effects of pimobendan injection in clinically healthy cats

Pimobendan is not currently approved for use in cats, although its usefulness in feline hypertrophic cardiomyopathy has been suggested. Reports indicate an increase in arrhythmic events following oral administration to healthy cats. Given the greater potency of intravenous administration compared to oral intake, it is conceivable that the incidence of arrhythmias may be increased following pimobendan injection. Therefore, this study aimed to investigate the proarrhythmic effects of pimobendan injection in cats. Five clinically healthy cats underwent physical examination, echocardiography, blood pressure measurements, and 24-hour Holter electrocardiography immediately before and after receiving pimobendan as an intravenous bolus dose of 0.15 mg/kg twice daily for 3 days. Additionally, a 24-hour Holter electrocardiography recording was conducted on the third day of pimobendan or placebo IV administration to assess heart rate, arrhythmias, and heart rate variability. Following pimobendan administration, there was a significant increase in total 24-hour heart rate. Echocardiography revealed a significant increase in mitral valve annulus systolic velocity (S') on the ventricular septal wall side, indicative of enhanced contractility. Only one cat exhibited paroxysmal ventricular tachycardia and an increase in the frequency of arrhythmic events. Conversely, in the remaining cats, a decreasing trend in the number of arrhythmias was observed. These findings indicate that intravenous administration of pimobendan may not be implicated in the onset of arrhythmias. Nevertheless, further research is warranted to explore the effects of intravenous pimobendan administration in cats with myocardial disease.

Aortic annular plane systolic excursion in cats with hypertrophic cardiomyopathy

BACKGROUND

Impairment of left ventricular (LV) longitudinal function is an early marker of systolic dysfunction in hypertrophic cardiomyopathy (HCM). Aortic annular plane systolic excursion (AAPSE) is a measure of LV longitudinal function in people that has not been evaluated in cats.

HYPOTHESIS

Aortic annular plane systolic excursion is lower in cats with HCM compared to control cats, and cats in stage C have the lowest AAPSE.

ANIMALS

One hundred seventy-five cats: 60 normal, 61 HCM stage B and 54 HCM stage C cats.

MATERIALS

Multicenter retrospective case-control study. Electronic medical records from 4 referral hospitals were reviewed for cats diagnosed with HCM and normal cats. HCM was defined as LV wall thickness ≥6 mm and normal cats ≤5 mm. M-mode bisecting the aorta in right parasternal short-axis view was used to measure AAPSE.

RESULTS

Aortic annular plane systolic excursion was lower in HCM cats compared to normal cats (3.9 ± 0.9 mm versus 4.6 ± 0.9 mm, P < .001) and was lowest in HCM stage C (2.4 ± 0.6 mm, P < .001). An AAPSE <2.9 mm gave a sensitivity of 83% (95% CI 71%-91%) and specificity of 92% (95% CI 82%-97%) to differentiate HCM stage C from stage B. AAPSE correlated with mitral annular plane systolic excursion (r = .6 [.4-.7], P < .001), and atrial fractional shortening (r = .6 [.5-.7], P < .001), but showed no correlation with LV fractional shortening.

CONCLUSIONS AND CLINICAL IMPORTANCE

Aortic annular plane systolic excursion is an easily acquired echocardiographic variable and might be a new measurement of LV systolic performance in cats with HCM.

Pharmacokinetics of pimobendan after oral administration to dogs with myxomatous mitral valve disease

BACKGROUND

Pimobendan is an important therapy for dogs with myxomatous mitral valve disease (MMVD). The pharmacokinetics are reported in healthy dogs but not in dogs with heart disease.

HYPOTHESIS/OBJECTIVES

To determine if dog characteristics such as age, breed, body condition score, ACVIM stage of heart disease or biochemical laboratory value alter the pharmacokinetics of orally administered pimobendan and its metabolite in a cohort of dogs with naturally occurring MMVD.

ANIMALS

Fifty-seven client-owned dogs with MMVD ACVIM Stage B2, C, or D and administered pimobendan to steady state blood concentrations.

METHODS

Prospective, observational study. Samples were collected using a sparse-sampling protocol at specific intervals after administration of pimobendan. Plasma pimobendan and the active metabolite (O-desmethyl-pimobendan, ODMP) concentrations were determined via high-pressure liquid chromatography and fluorescence detection. Data was analyzed via a population pharmacokinetic approach and nonlinear mixed effects modeling (NLME). Numerous covariates were examined in the NLME model.

RESULTS

The absorption and elimination half-lives (t1/2 ) were approximately 1.4 and 1 hour for pimobendan and 1.4 and 1.3 hours for ODMP, respectively. Pharmacokinetic parameters were highly variable, especially the values for pimobendan absorption and elimination rate, and absorption rate of ODMP with coefficients of variation of 147.84%, 64.51% and 64.49%, respectively. No covariate evaluated was a significant source of variability.

CONCLUSIONS AND CLINICAL IMPORTANCE

The pharmacokinetic parameters were highly variable among this group of dogs with MMVD. The variability was not associated with the dog's age, body weight or condition score, stage of heart disease, dose, serum creatinine, or alkaline phosphatase.

Pimobendan prevents cardiac dysfunction, mitigates cardiac mitochondrial dysfunction, and preserves myocyte ultrastructure in a rat model of mitral regurgitation

BACKGROUND

Pimobendan has been proven to delay the onset of congestive heart failure (CHF) in dogs with mitral regurgitation (MR); however, molecular underlying mechanisms have not been fully elucidated. This study aimed to investigate (1) the effects of pimobendan on cardiac function, cardiac mitochondrial quality and morphology, and cardiac ultrastructure in a rat model of chronic MR and (2) the direct effect of pimobendan on intracellular reactive oxygen species (ROS) production in cardiac cells. MR was surgically induced in 20 Sprague-Dawley rats, and sham procedures were performed on 10 rats. Eight weeks post-surgery, the MR rats were randomly divided into two groups: the MR group and the MR + pimobendan group. Pimobendan (0.15 mg/kg) was administered twice a day via oral gavage for 4 weeks, whereas the sham and MR groups received equivalent volumes of drinking water. Echocardiography was performed at baseline (8 weeks post-surgery) and at the end of the study (4 weeks after treatment). At the end of the study protocol, all rats were euthanized, and their hearts were immediately collected, weighed, and used for transmission electron microscopy and mitochondrial quality assessments. To evaluate the role of pimobendan on intracellular ROS production, preventive or scavenging properties were tested with H2O2-induced ROS generation in rat cardiac myoblasts (H9c2).

RESULTS

Pimobendan preserved cardiac functions and structure in MR rats. In addition, pimobendan significantly improved mitochondrial quality by attenuating ROS production and depolarization (P < 0.05). The cardiac ultrastructure and mitochondrial morphology were significantly preserved in the MR + pimobendan group. In addition, pimobendan appeared to play as a ROS scavenger, but not as a ROS preventer, in H2O2-induced ROS production in H9c2 cells.

CONCLUSIONS

Pimobendan demonstrated cardioprotective effects on cardiac function and ultrastructure by preserving mitochondrial quality and acted as an ROS scavenger in a rat model of MR.

Effects of Intravenous Pimobendan on Cardiovascular Parameters in Healthy Sedated Cats

This study aimed to investigate the effects of intravenous pimobendan on cardiovascular function and to determine the appropriate dose for clinical usage in cats. Six purpose-bred cats received one of the following treatments: intravenous pimobendan at a single dose of 0.075 mg/kg (low dose [LD] group), 0.15 mg/kg (middle dose [MD] group), 0.3 mg/kg (high dose [HD] group), or saline at 0.1 mL/kg (placebo group). Echocardiography and blood pressure measurements were performed before and 5, 15, 30, 45, and 60 minute after drug administration for each treatment. In the MD and HD groups, the fractional shortening, peak systolic velocity, cardiac output, and heart rate increased significantly. There were no significant differences in blood pressure among the groups. Intravenous pimobendan at 0.15-0.3 mg/kg increased the fractional shortening, peak systolic velocity, cardiac output in healthy cats.

Repeated-Dose Pharmacodynamics of Pimobendan in Healthy Cats

Simple Summary

The dosing of pimobendan in cats is determined with reference to the effects of a single dose, although pimobendan is normally administered in repeated doses. In this study, the pharmacodynamics of repeated and multiple-dose pimobendan in healthy cats was investigated. Data were collected from five cats. Cardiac systolic function increased after repeated-dose pimobendan administration and correlated well with plasma concentrations of the drug. The results of this study suggest that a higher dose of pimobendan is effective.

Abstract

The aims of this study were to investigate the effects of repeated and multiple-dose pimobendan on cardiac systolic function and the correlations between changes in cardiac systolic function and plasma concentrations of pimobendan and O-desmethylpimobendan (ODMP). Five clinically healthy cats were subjected to four different medication protocols for 14 days, with a washout period of at least 1 month between each protocol. The protocols were pimobendan 0.5 mg/kg q12h (high dosage [HD] group); pimobendan 0.25 mg/kg q12h (standard dosage [SD] group); pimobendan 0.125 mg/kg q12h (low dosage group); and Biofermin R, one tablet q12h (placebo group). Echocardiography and measurement of plasma concentrations of pimobendan and ODMP were performed prior to medication administration (baseline) and 20, 40, 60, 120, 240, 360, and 480 min after administration, and the correlation between the changes in cardiac systolic function and plasma concentration of pimobendan, ODMP, or the sum of both were examined. The cardiac systolic function increased in the HD and SD groups, and there were significant correlations between the lateral peak systolic myocardial velocity (S′) changes and plasma pimobendan, plasma ODMP, and the sum of both. Repeated doses of pimobendan in healthy cats increased cardiac systolic function, and there were significant correlations between cardiac function and plasma concentrations of pimobendan and ODMP. The results of this study highlight the effectiveness of a higher dose of pimobendan.

Preliminary Bioequivalence of an Oral Pimobendan Solution Formulation with Reference Solution Formulation in Beagle Dogs

Oral capsule and tablet formulations of pimobendan are widely used but may present difficulties for accurately dosing small patients. This study aimed to compare the pharmacokinetic (PK) characteristics, bioequivalence, and cardiovascular effects of a custom-made oral pimobendan solution (PS) formulation compared to a reference solution (RS) formulation in conscious, healthy dogs. A randomized crossover design was performed on dogs that received RS and PS formulations at a dose of 0.3 mg/kg. Blood samples were collected at 0, 0.083, 0.167, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 8, and 24 h after oral administration for PK analysis; bioequivalence was also calculated. Echocardiography was also performed to assess the cardiovascular effects. The results revealed that the plasma concentrations of pimobendan and o-desmethyl-pimobendan (active metabolite) in the case of both formulations were comparable. The relative ratios of geometric mean concentrations for all significant parameters of PK were within a range of 80–125%, indicating bioequivalence. In addition, both formulations increased cardiac contraction significantly when compared with the baseline, and no differences in cardiac contractility were detected between the formulations. The PS formulation can be used as alternative to the RS formulation for the management of congestive heart disease because of the bioequivalence between the two formulations.

Pharmacokinetics of pimobendan following oral administration to New Zealand White rabbits (Oryctolagus cuniculus)

OBJECTIVE

To determine the pharmacokinetics and potential adverse effects of pimobendan after oral administration in New Zealand White rabbits (Ocytolagus cuniculi).

ANIMALS

10 adult sexually intact (5 males and 5 females) rabbits.

PROCEDURES

2 pilot studies were performed with a pimobendan suspension or oral tablets. Eight rabbits received 7.5 mg of pimobendan (mean 2.08 mg/kg) suspended in a critical care feeding formula. Plasma concentrations of pimobendan and O-demethylpimobendan (ODMP) were measured, and pharmacokinetic parameters were calculated for pimobendan by noncompartmental analysis. Body weight, food and water consumption, mentation, urine, and fecal output were monitored.

RESULTS

Mean ± SD maximum concentration following pimobendan administration was 15.7 ± 7.54 ng/mL and was detected at 2.79 ± 1.25 hours. The half-life was 3.54 ± 1.32 hours. Plasma concentrations of pimobendan were detectable for up to 24 hours. The active metabolite, ODMP, was detected in rabbits for 24 to 36 hours. An adverse event occurred following administration of pimobendan in tablet form in 1 pilot study, resulting in death secondary to aspiration. No other adverse events occurred.

CLINICAL RELEVANCE

Plasma concentrations of pimobendan were lower than previously reported for dogs and cats, despite administration of higher doses, and had longer time to maximum concentration and half-life. Based on this study, 2 mg/kg of pimobendan in a critical care feeding formulation should maintain above a target plasma concentration for 12 to 24 hours. However, further studies evaluating multiple-dose administration as well as pharmacodynamic studies and clinical trials in rabbits with congestive heart failure are needed to determine accurate dose and frequency recommendations.

The Feline Cardiomyopathies: 2. Hypertrophic cardiomyopathy

Practical relevance:

Hypertrophic cardiomyopathy (HCM) is the most common form of feline cardiomyopathy observed clinically and may affect up to approximately 15% of the domestic cat population, primarily as a subclinical disease. Fortunately, severe HCM, leading to heart failure or arterial thromboembolism (ATE), only occurs in a small proportion of these cats.

Patient group:

Domestic cats of any age from 3 months upward, of either sex and of any breed, can be affected. A higher prevalence in male and domestic shorthair cats has been reported.

Diagnostics:

Subclinical feline HCM may or may not produce a heart murmur or gallop sound. Substantial left atrial enlargement can often be identified radiographically in cats with severe HCM. Biomarkers should not be relied on solely to diagnose the disease. While severe feline HCM can usually be diagnosed via echocardiography alone, feline HCM with mild to moderate left ventricular (LV) wall thickening is a diagnosis of exclusion, which means there is no definitive test for HCM in these cats and so other disorders that can cause mild to moderate LV wall thickening (eg, hyperthyroidism, systemic hypertension, acromegaly, dehydration) need to be ruled out.

Key findings:

While a genetic cause of HCM has been identified in two breeds and is suspected in another, for most cats the cause is unknown. Systolic anterior motion of the mitral valve (SAM) is the most common cause of dynamic left ventricular outflow tract obstruction (DLVOTO) and, in turn, the most common cause of a heart murmur with feline HCM. While severe DLVOTO is probably clinically significant and so should be treated, lesser degrees probably are not. Furthermore, since SAM can likely be induced in most cats with HCM, the distinction between HCM without obstruction and HCM with obstruction (HOCM) is of limited importance in cats. Diastolic dysfunction, and its consequences of abnormally increased atrial pressure leading to signs of heart failure, and sluggish atrial blood flow leading to ATE, is the primary abnormality that causes clinical signs and death in affected cats. Treatment (eg, loop diuretics) is aimed at controlling heart failure. Preventive treatment (eg, antithrombotic drugs) is aimed at reducing the risk of complications (eg, ATE).

Conclusions:

Most cats with HCM show no overt clinical signs and live a normal or near-normal life despite this disease. However, a substantial minority of cats develop overt clinical signs referable to heart failure or ATE that require treatment. For most cats with clinical signs caused by HCM, the long-term prognosis is poor to grave despite therapy.

Areas of uncertainty:

Genetic mutations (variants) that cause HCM have been identified in a few breeds, but, despite valiant efforts, the cause of HCM in the vast majority of cats remains unknown. No treatment currently exists that reverses or even slows the cardiomyopathic process in HCM, again despite valiant efforts. The search goes on.

Effect of a single dose of pimobendan on right ventricular and right atrial function in 11 healthy cats

OBJECTIVES

The objective of this study was to investigate the effect of pimobendan on echocardiographic parameters of right ventricular and atrial function in healthy cats.

ANIMALS

Eleven privately owned, healthy adult cats.

MATERIAL AND METHODS

Each cat underwent five echocardiographic examinations: the first and second examinations were performed 1 h apart on day 0. On day 1, the third examination served as baseline, whereas the fourth and fifth examinations were performed one and 6 h after administration of a single oral dose of pimobendan (1.25 mg/cat), respectively. Parameters of right ventricular and atrial morphology and function were collected and compared among time points.

RESULTS

Pimobendan administration produced a change in some echocardiographic variables. Specifically, heart rate, right ventricular fractional shortening and peak velocity of systolic lateral tricuspid annular motion increased (P = 0.032, P = 0.002 and P < 0.001, respectively), whereas right ventricular end-systolic internal diameter and right atrial maximum and minimum internal diameters decreased (P = 0.004, P = 0.025 and P = 0.01, respectively). Right ventricular fractional area change and tricuspid annular plane systolic excursion did not change.

CONCLUSIONS

This novel study showed that pimobendan had positive effects on right ventricular and right atrial function in healthy cats. Further studies are needed to determine whether pimobendan has similar effects in cats with cardiac diseases.

A pilot study investigating the effect of pimobendan on the cardiac rhythm and selected echocardiographic parameters of healthy cats

INTRODUCTION

The effects of pimobendan on the heart rhythm in cats are unknown. The purpose of this pilot study was to evaluate the effect of pimobendan on the cardiac rhythm and selected echocardiographic parameters of cats.

ANIMALS, MATERIALS, AND METHODS

Six clinically healthy cats received each of four medication protocols for 15 days, with a washout period of at least one month between each protocol. The protocols were, pimobendan 0.5 mg/kg twice daily (high dosage group), pimobendan 0.25 mg/kg twice daily (standard dosage group), pimobendan 0.125 mg/kg twice daily (low dosage group), and Biofermin R, one tablet twice daily (placebo group). Twenty-four-hour ambulatory electrocardiogram recordings, blood pressure measurements, and echocardiographic examinations were performed after two weeks of each medication protocol. Electrocardiographic, echocardiographic, and blood pressure parameters were compared between the four groups.

RESULTS

The total number of escape/idioventricular/idiojunctional complexes in the high dosage group was significantly higher compared with the placebo, low dosage, and standard dosage groups (p < 0.001). The blood pressure; total number of heart beats per day; and mean, minimum, and maximum heart rates were not significantly different between the groups. The longitudinal strain rate and calculated cardiac output were significantly increased in the high and standard dosage groups.

CONCLUSIONS

The administration of pimobendan, especially at high doses, was associated with increased numbers of escape/idioventricular/idiojunctional complexes in some cats and echocardiographic parameters. Further studies are warranted to investigate both the mechanism underlying the observed changes and what, if any, clinical implications these changes might have in cats with heart disease.

P-Wave Terminal Force in Dogs With Myxomatous Mitral Valve Disease

P-wave terminal force (PTF) is accepted as an electrocardiographic criteria to assess left atrial abnormalities in humans. In this study, the applicability of PTF in dogs with myxomatous mitral valve disease (MMVD) was evaluated, and compared its ability to identify left atrial dilatation with 4 other P-wave derived parameters. Seventy-four dogs with echocardiographically diagnosed MMVD were recruited for this prospective cross-sectional study. Also, 47 healthy dogs were included to serve as controls. All dogs underwent physical, electrocardiographic and standard echocardiographic examinations prior to enrollment. Electrocardiographic measurements were obtained from simultaneous recordings at three different locations for precordial lead V₁. PTF was defined as the deflection following the second half of the P-wave, and was best documented at the first and third right intercostal spaces. In those locations, the P-wave was negative and P-wave terminal force was recognized as a positive undulation in baseline following P-wave. P-wave terminal force and P-wave duration measured from recordings obtained at either the first or third right intercostal spaces had poor to weak correlations (P < .05) with echocardiographic surrogates of cardiac remodeling and congestion. In dogs with MMVD, only P-wave duration and P-wave area distinguished normal and dilated left atria (P < .05). In conclusion, PTF had positive polarity and was best recorded when precordial lead V₁ electrode was placed at the most cranial right intercostal locations. PTF failed to reliably identify left atrial enlargement in dogs with MMVD.

Acute pharmacodynamic effects of pimobendan in client-owned cats with subclinical hypertrophic cardiomyopathy

BACKGROUND

Prior studies have suggested that pimobendan is associated with several positive effects in cats, including improved survival in cats with congestive heart failure and improved left atrial function in research colony cats with hypertrophic cardiomyopathy (HCM) and normal cats. However, there is still a paucity of pharmacodynamic data refuting or supporting the use of pimobendan in a clinical cat population. This clinical trial aimed to evaluate the pharmacodynamic effects and tolerability of a single dose of pimobendan in cats with HCM. Echocardiograms and Doppler-derived systolic blood pressures were performed in 21 client-owned cats with subclinical HCM at baseline and 90-min after oral administration of 1.25 mg of pimobendan (Vetmedin). Seven additional cats were evaluated post-placebo administration to account for intra-day variability.

RESULTS

Heart rate, systolic blood pressure, and murmur grade were not significantly different between baseline and post-pimobendan evaluations. Left auricular blood flow velocity, left atrial size, and left ventricular fractional shortening were not significantly different between baseline and post-pimobendan evaluations. Mean (± standard deviation) tissue Doppler peak systolic velocity of the mitral annulus was significantly higher following pimobendan (7.4 cm/s ± 1.5 vs 8.5 ± 1.6; p = 0.02). Median (min, max) left-ventricular outflow tract maximum velocity was significantly higher following pimobendan [1.9 m/sec (1.5, 3.4) vs 2.6 m/sec (2.0, 4.0); p = 0.01]. Mean right-ventricular outflow tract maximum velocity was also significantly higher following pimobendan (1.5 m/s ± 0.51 vs 2.0 ± 0.53; p = 0.004). Mean left atrial fractional shortening was significantly higher following pimobendan (28% ± 6 vs 32% ± 7; p = 0.02). No adverse events were observed following pimobendan administration. Right ventricular outflow tract velocity was significantly higher following placebo in control cats (1.02 ± 0.21 versus 1.31 ± 0.31; p = 0.01). No other significant differences were detected.

CONCLUSIONS

In client-owned cats with HCM, pimobendan acutely increased left atrial function and mildly increased left ventricular systolic function. Left ventricular outflow tract velocity was increased after pimobendan. Pimobendan was well tolerated in the acute setting in cats with HCM. The findings of this prospective, acute-dosing study confirm previous findings in research animals and retrospective analyses and suggest that chronic dosing studies are safe and warranted.

Effects of pimobendan in cats with hypertrophic cardiomyopathy and recent congestive heart failure: Results of a prospective, double-blind, randomized, nonpivotal, exploratory field study

Background

The benefits of pimobendan in the treatment of congestive heart failure (CHF) in cats with hypertrophic cardiomyopathy (HCM) have not been evaluated prospectively.

Hypothesis/Objectives

To investigate the effects of pimobendan in cats with HCM and recent CHF and to identify possible endpoints for a pivotal study. We hypothesized that pimobendan would be well‐tolerated and associated with improved outcome.

Animals

Eighty‐three cats with HCM and recently controlled CHF: 30 with and 53 without left ventricular outflow tract obstruction.

Methods

Prospective randomized placebo‐controlled double‐blind multicenter nonpivotal field study. Cats received either pimobendan (0.30 mg/kg q12h, n = 43), placebo (n = 39), or no medication (n = 1) together with furosemide (<10 mg/kg/d) with or without clopidogrel. The primary endpoint was a successful outcome (ie, completing the 180‐day study period without a dose escalation of furosemide).

Results

The proportion of cats in the full analysis set population with a successful outcome was not different between treatment groups (P = .75). For nonobstructive cats, the success rate was 32% in pimobendan‐treated cats versus 18.2% in the placebo group (odds ratio [OR], 2.12; 95% confidence interval [CI], 0.54‐8.34). For obstructive cats, the success rate was 28.6% and 60% in the pimobendan and placebo groups, respectively (OR, 0.27; 95% CI, 0.06‐1.26). No difference was found between treatments for the secondary endpoints of time to furosemide dose escalation or death (P = .89). Results were similar in the per‐protocol sets. Adverse events in both treatment groups were similar.

Conclusions and Clinical Importance

In this study of cats with HCM and recent CHF, no benefit of pimobendan on 180‐day outcome was identified.

Effects of pimobendan on left atrial transport function in cats

BACKGROUND

Arterial thromboembolism is a sequela of hypertrophic cardiomyopathy (HCM) in cats related to left atrial (LA) enlargement and dysfunction.

HYPOTHESIS

Pimobendan improves LA transport function in cats.

ANIMALS

Twenty-two client-owned cats with HCM and 11 healthy cats.

METHODS

Prospective, double-blind, randomized, placebo-controlled clinical cohort study. Cats were randomized to receive either pimobendan (0.25 mg/kg PO q12h) or placebo for 4 to 7 days. Nineteen echocardiographic variables of LA size and function were evaluated. Statistical comparisons included t tests, analysis of variance, and multivariable analyses.

RESULTS

Peak velocity of left auricular appendage flow (LAapp peak; mean ± SD, 0.85 ± 0.20 vs 0.71 ± 0.22 m/s; P = .01), maximum LA volume (P = .03), LA total emptying volume (P = .03), peak velocity of late diastolic transmitral flow (A peak velocity; 0.77 ± 0.12 vs 0.62 ± 0.17 m/s; P = .05), and A velocity time integral (A VTI; 3.05 ± 0.69 vs 3.37 ± 0.49; P = .05) were increased after pimobendan. Mean change after pimobendan was larger in cats with HCM compared to healthy cats for LA fractional shortening (2.1% vs -2.1%; P = .05), A VTI (0.58 vs 0.01 cm; P = .01), LAapp peak (0.20 vs 0.02 m/s; P = .02), LA kinetic energy (3.51 vs -0.10 kdynes-cm; P = .05), and LA ejection force (1.93 vs -0.07 kdynes; P = .01) in the multivariable model. The stronger effect of pimobendan in cats with HCM was independent of LA size.

CONCLUSIONS AND CLINICAL IMPORTANCE

We identified positive, albeit minor, effects of pimobendan on LA function in cats with HCM. Whether or not treatment with pimobendan decreases the risk of cardiogenic embolism deserves further study.

Retrospective evaluation of the safety and tolerability of pimobendan in cats with obstructive vs nonobstructive cardiomyopathy

BACKGROUND

Pimobendan is frequently used off-label for treatments of cats with congestive heart failure (CHF). Concern exists regarding the safety of pimobendan in cats with outflow tract obstruction (OTO).

OBJECTIVES

In cats treated with pimobendan, incidence of adverse effects will not differ between cats with OTO vs cats with nonobstructive cardiomyopathy.

ANIMALS

Two-hundred sixty cats with CHF (57 with OTO, 203 with nonobstructive disease).

METHODS

Retrospective medical record review. Groups were compared using 2-sample t-tests, Wilcoxon rank-sum tests, and Fisher exact tests.

RESULTS

Compared to cats with nonobstructive cardiomyopathy, cats with OTO were younger (8.9 [interquartile range (IQR) 6.6] vs 10.8 [6.3] years, P = .0036), more likely to have a heart murmur (51/57 [90%] vs 76/203 [37.8%] cats, P < .0001), more likely to manifest CHF as pulmonary edema (53/57 [83%] vs 144/203 [70.9%] cats, P = .0004), and less likely to have pleural effusion (19/57 [33%] vs 122/203 [60.1%] cats, P = .0005). Adverse effects suspected to be related to pimobendan administration occurred in 12/260 cats (4.6%), including 11/203 cats (5.4%) with nonobstructive cardiomyopathy and 1/57 cat (2%) with OTO (P = .7). Pimobendan was discontinued due to adverse effects in 4/260 cats (1.5%), 3 with nonobstructive disease and 1 with OTO (P = 1.0). Acute adverse hemodynamic effects after pimobendan administration were not detected in any cats.

CONCLUSIONS AND CLINICAL IMPORTANCE

Pimobendan is well tolerated in cats with cardiomyopathy and CHF, regardless of the presence of OTO.

Pharmacokinetics of Pimobendan and Its Metabolite O-Desmethyl-Pimobendan Following Rectal Administration to Healthy Dogs

Objective: This study describes the pharmacokinetics of parent pimobendan (PIM) and its active metabolite, o-desmethyl-pimobendan (ODMP), after oral and rectal administration of pimobendan to healthy dogs.

Animals: A total of eight healthy privately owned dogs were used in this study.

Procedures: The dogs received a single dose (0.5 mg/kg) of a commercially available pimobendan tablet per os (PO). Twelve blood samples were collected over a 12-h period for pharmacokinetic analysis. After a 24-h washout period, the dogs received the same dose of pimobendan solution per rectum (PR), and samples were obtained at the same time for analysis.

Results: For PIM, PO vs. PR, respectively, the mean maximum plasma concentration (C_max, ng/ml) was 49.1 ± 28.7 vs. 10.1 ± 2, the time to reach a maximum concentration (T_max, h) was 2.1 ± 0.9 vs. 1 ± 0.4, the disappearance half-life (t_1/2, h) was 1.8 ± 0.8 vs. 2.2 ± 0.6, and the area under the concentration–time curve (AUC, ng^*h/ml) was 148.4 ± 71.6 vs. 31.1 ± 11.9, with relative bioavailability (F, %) of 25 ± 8. For ODMP, PO vs. PR, respectively, C_max was 30.9 ± 10.4 vs. 8.8 ± 4.8, T_max was 3.2 ± 1.6 vs. 1.7 ± 1.1, and t_1/2 was 5.0 ± 2.7 vs. 8.3 ± 4.8, with AUC of 167.8 ± 36.2 vs. 50.1 ± 19.2 and F of 28 ± 6. The differences between PO and PR were significant (P < 0.03) for AUC and C_max for both PIM and ODMP.

Conclusions and Clinical Relevance: The pharmacokinetics of PIM and ODMP were described following PO and PR administration. The findings suggest that pimobendan PR might achieve effective concentrations and, as such, warrant future studies of clinical effectiveness in treating dogs with congestive heart failure and which are unable to receive medication PO.

Effect of pimobendan on left atrial function: an echocardiographic pilot study in 11 healthy cats

OBJECTIVES

- To evaluate the effect of a single dose of pimobendan on left atrial (LA) function in healthy cats.

ANIMALS

- Eleven client owned healthy cats.

MATERIAL AND METHODS

- Standardized and repeated echocardiographic examinations were performed on healthy and conscious cats before and after a single dose of orally administered pimobendan (1.25 mg/cat). Left atrial systolic functional parameters were assessed.

RESULTS

- Some of the tested parameters of LA function showed significant improvement after pimobendan administration, whereas no significant effect on left ventricular function was observed. In particular, LA minimal diameters obtained from M-mode images in short (p=0.018) and long (p=0.009) axis reduced after pimobendan administration, whereas LA fractional shortening from short (p=0.027) and long (p=0.042) axis and LA appendage emptying velocity (p<0.001) significantly increased. A mild increase in heart rate (p=0.001), and a transient increase on the peak systolic wave pulmonary vein velocity (p=0.008) were also recorded as a possible effect.

CONCLUSIONS

- A single dose of pimobendan appears to impact LA function in healthy cats. However, because of the small number of cats included, and the absence of a placebo group, these results cannot be definitively separated from the effect of time. Additional studies are needed to understand if similar effects are observed in cats with cardiomyopathy and LA dilatation.

Left atrial size and volume in cats with primary cardiomyopathy with and without congestive heart failure

INTRODUCTION/OBJECTIVES

Myocardial diseases are the most common acquired cardiac diseases in cats and may result in left atrial enlargement and congestive heart failure (CHF). Volume calculations have replaced linear measurements for chamber quantification in humans but are not commonly measured in cats. The aims of this retrospective study were to compare the left atrial (LA) size by two-dimensional linear measurements to two-dimensional LA volumes (LAV).

ANIMALS

One hundred sixty-two client-owned cats were included.

MATERIALS AND METHODS

Cats with complete echocardiographic examinations were included and categorized into one of the three groups: healthy, cardiomyopathy (CM), and CHF. Seven measurements of the LA size were performed including minimal and maximal LA-to-aortic ratio (LA:Ao) and LAV and also maximal left atrial diameter (LAD).

RESULTS

Cats were classified as healthy (n = 56), CM (n = 62), and CHF (n = 44). The minimal LA:Ao (LA:Ao_min) and minimal LAV from the left apical view (LAV_min-LAP) best differentiated the CM and CHF groups. The LA:Ao_min value with the optimal sensitivity and specificity to distinguish CM and CHF cats was 1.64 (sensitivity 84% and specificity 75%).

CONCLUSIONS

Left atrial volumes were not superior to linear measurements of LA size in distinguishing CM and CHF cats in this study. Minimal LA size and volumes resulted in a larger area under the curve than each corresponding maximal value. Minimum LA size may be a better prognostic factor of CHF in cats with CM.

Cardiac Effects of a Single Dose of Pimobendan in Cats With Hypertrophic Cardiomyopathy; A Randomized, Placebo-Controlled, Crossover Study

Background: Pimobendan has been shown to impart a significant survival benefit in cardiomyopathic cats who receive it as part of heart failure therapy. However, use of pimobendan remains controversial in cats with hypertrophic cardiomyopathy (HCM) due to lack of pharmacodynamic data for pimobendan in cats with HCM and due to theoretical concerns for exacerbating left ventricular outflow tract obstructions. Hypothesis/Objectives: Our objective was to investigate the cardiac effects of pimobendan in cats with HCM. We hypothesized that pimobendan would not exacerbate left ventricular outflow tract obstructions and that it would improve echocardiographic measures of diastolic function. Animals: Thirteen purpose-bred cats were studied from a research colony with naturally-occurring HCM due to a variant in myosin binding protein C. Methods: Cats underwent two examinations 24 h apart with complete standard echocardiography. On their first day of evaluation, they were randomized to receive oral placebo or 1.25 mg pimobendan 1 h prior to exam. On their second examination, they were crossed over and received the remaining treatment. Investigators were blinded to all treatments. Results: The pimobendan group had a significant increase in left atrial fractional shortening (pimobendan group 41.7% ± 5.9; placebo group 36.1% ± 6.0; p = 0.04). There was no significant difference in left ventricular outflow tract (LVOT) velocities between the groups (pimobendan group 2.8 m/s ± 0.8; placebo group 2.6 m/s ± 1.0). There were no significant differences between the number of cats with LVOT obstructions between groups (12 in pimobendan group; 11 in placebo group; p = 1.00). There were no detectable differences in any systolic measures, including left ventricular fractional shortening, mitral annular plane systolic excursion, and tricuspid annular plane systolic excursion. Doppler-based diastolic function assessment was precluded by persistent tachycardia. Conclusions: Improved left atrial function in the pimobendan group could explain some of the reported survival benefit for HCM cats in CHF. Pimobendan did not exacerbate LVOT obstructions and thus may not be contraindicated in HCM cats with LVOT obstructions. Future studies are needed to better characterize other physiologic effects, particularly regarding diastolic function assessment, and to better assess safety of pimobendan over a longer time-course.

Cardiac Effects of a Single Dose of Pimobendan in Cats With Hypertrophic Cardiomyopathy; A Randomized, Placebo-Controlled, Crossover Study

Background: Pimobendan has been shown to impart a significant survival benefit in cardiomyopathic cats who receive it as part of heart failure therapy. However, use of pimobendan remains controversial in cats with hypertrophic cardiomyopathy (HCM) due to lack of pharmacodynamic data for pimobendan in cats with HCM and due to theoretical concerns for exacerbating left ventricular outflow tract obstructions.

Hypothesis/Objectives: Our objective was to investigate the cardiac effects of pimobendan in cats with HCM. We hypothesized that pimobendan would not exacerbate left ventricular outflow tract obstructions and that it would improve echocardiographic measures of diastolic function.

Animals: Thirteen purpose-bred cats were studied from a research colony with naturally-occurring HCM due to a variant in myosin binding protein C.

Methods: Cats underwent two examinations 24 h apart with complete standard echocardiography. On their first day of evaluation, they were randomized to receive oral placebo or 1.25 mg pimobendan 1 h prior to exam. On their second examination, they were crossed over and received the remaining treatment. Investigators were blinded to all treatments.

Results: The pimobendan group had a significant increase in left atrial fractional shortening (pimobendan group 41.7% ± 5.9; placebo group 36.1% ± 6.0; p = 0.04). There was no significant difference in left ventricular outflow tract (LVOT) velocities between the groups (pimobendan group 2.8 m/s ± 0.8; placebo group 2.6 m/s ± 1.0). There were no significant differences between the number of cats with LVOT obstructions between groups (12 in pimobendan group; 11 in placebo group; p = 1.00). There were no detectable differences in any systolic measures, including left ventricular fractional shortening, mitral annular plane systolic excursion, and tricuspid annular plane systolic excursion. Doppler-based diastolic function assessment was precluded by persistent tachycardia.

Conclusions: Improved left atrial function in the pimobendan group could explain some of the reported survival benefit for HCM cats in CHF. Pimobendan did not exacerbate LVOT obstructions and thus may not be contraindicated in HCM cats with LVOT obstructions. Future studies are needed to better characterize other physiologic effects, particularly regarding diastolic function assessment, and to better assess safety of pimobendan over a longer time-course.