Pharmacokinetics and cardiovascular effects following a single oral administration of a nonaqueous pimobendan solution in healthy dogs

Changes in echocardiographic indices and left ventricular strain values by two-dimensional speckle-tracking echocardiography following pre-anesthetic oral pimobendan administration compared with intravenous pimobendan in dogs

Introduction

The effects of pre-anesthetic single-dose oral pimobendan during inhalational anesthesia, including the comparison with the effects of single intravenous pimobendan under anesthesia, remain unexplored. Therefore, this study aimed to determine changes in hemodynamic and echocardiographic parameters induced by pre-anesthetic administration of oral pimobendan under isoflurane general anesthesia and to compare them with those induced by intravenous pimobendan.

Methods

Thirteen clinically normal dogs (4 laboratory and 9 client-owned dogs) with no clinical signs and not on any medical treatment were included. Anesthesia was performed three times: no pimobendan (Control), oral pimobendan (PIMO PO, 0.3 mg/kg), and intravenous pimobendan (PIMO IV, 0.15 mg/kg). Echocardiographic and hemodynamic parameters were monitored at 30-min intervals in all groups.

Results

Compared to the Control group, end-systolic volume index (ESVI) and normalized left ventricular internal diameter at end-systole (LVIDSN) were significantly lower, and fractional shortening (FS) and ejection fraction (EF) were significantly higher in the PIMO PO and IV groups (p < 0.001). Global radial strain (GRS) was significantly higher in the PIMO PO and IV groups (p = 0.015).

Conclusion

Under general anesthesia, oral pimobendan preserved LV systolic and myocardial function in a manner comparable to intravenous pimobendan. Pre-anesthetic administration of oral pimobendan can be used to compensate for cardiac systolic function in dogs who require therapeutic and diagnostic procedures under general anesthesia with potential risk of circulatory failure.

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.

No impact of polymorphism in the phosphodiesterase 5A gene in Cavalier King Charles Spaniels on pimobendan-induced inhibition of platelet aggregation response

BACKGROUND

A variant in the canine phosphodiesterase (PDE) 5A gene (PDE5A:E90K) is associated with decreased concentrations of circulating cyclic guanosine monophosphate (cGMP) and response to PDE5 inhibitor treatment. Pimobendan is a PDE inhibitor recommended for medical treatment of certain stages of myxomatous mitral valve disease (MMVD) in dogs.

HYPOTHESIS

PDE5A:E90K polymorphism attenuates the inhibitory effect of pimobendan on in vitro platelet aggregation and increases basal platelet aggregation in Cavalier King Charles Spaniels (CKCS). Selected clinical variables (MMVD severity, sex, age, hematocrit, platelet count in platelet-rich plasma [PRP], and echocardiographic left ventricular fractional shortening [LV FS]) will not show an association with results.

ANIMALS

Fifty-two privately owned CKCS with no or preclinical MMVD.

METHODS

Using blood samples, we prospectively assessed PDE5A genotype using Sanger sequencing and adenosine diphosphate-induced platelet aggregation response (area under the curve [AUC], maximal aggregation [MaxA], and velocity [Vel]) with and without pimobendan using light transmission aggregometry. Dogs also underwent echocardiography.

RESULTS

Pimobendan inhibited platelet function as measured by AUC, MaxA, and Vel at a concentration of 10 μM (P < .0001) and Vel at 0.03 μM (P < .001). PDE5A:E90K polymorphism did not influence the inhibitory effect of pimobendan or basal platelet aggregation response.

CONCLUSIONS AND CLINICAL IMPORTANCE

The PDE5A:E90K polymorphism did not influence in vitro basal platelet aggregation response or the inhibitory effect of pimobendan on platelet aggregation in CKCS. Dogs with the PDE5A:E90K polymorphism did not appear to have altered platelet function or response to pimobendan treatment.

MANAGEMENT OF SUSPECTED DILATED CARDIOMYOPATHY WITH PIMOBENDAN IN TWO LEOPARD SHARKS (TRIAKIS SEMIFASCIATA)

Two adult male leopard sharks (Triakis semifasciata) under managed care were diagnosed with suspected dilated cardiomyopathy. Clinical signs included lethargy, inappetence, and regurgitation. On cardiac ultrasound, fractional shortening was 14% and 10%, respectively (versus 21%-31% in four healthy conspecifics). Ventricular end-diastolic diameter to body weight ratio was 1.72 cm/kg in Case 1 (versus 0.52-1.24 cm/kg in four conspecifics). These results collectively suggested a dilated cardiomyopathy. Treatment was implemented with oral pimobendan at 0.3 mg/kg q48h for 1 mon. The pimobendan dose was increased to 0.5 mg/kg 3/wk, following plasmatic dosage of pimobendan and its metabolite. After 3 mon, fractional shortening increased to 38% and 20%, respectively, sharks regained a normal appetite, and body weight increased by 50% in one individual. After 2 yr, both individuals remained clinically normal, and no adverse effect was noted with pimobendan administration. Pimobendan plasma concentration suggested that this medication was well absorbed in this species.

Hemodynamic effect of pimobendan following intramuscular and intravenous administration in healthy dogs: A pilot study

Background

Pimobendan is widely used for the treatment of dogs with heart failure via the oral route. A new injectable form of pimobendan is now available and its potential usefulness via intravenous route has been recently demonstrated in dogs. However, the cardiovascular effects of intramuscular (IM) administration of injectable pimobendan have not been investigated yet.

Hypothesis

IM administration of pimobendan may have the same hemodynamic effect as the IV route.

Methods

Six healthy Beagle dogs underwent a placebo-controlled double-blind crossover study. The early cardiovascular effects after a single dose of IM and IV injections of pimobendan (0.2 ml/kg; Pimo IM and Pimo IV, respectively) were compared to the same volume of IM placebo (Saline IM) in anesthetized dogs. Clinical [heart rate (HR) and blood pressure (BP)] and echocardiographic hemodynamic parameters [left ventricular (LV) inflow waveforms of diastolic early wave (eV), atrial systolic wave (aV), diastolic early mitral ring velocity (e′), peak velocity (pV), stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR)] were monitored with 15 min intervals for 120 min.

Results

Diastolic BP decreased significantly at 30 min in Pimo IM compared to Saline IM. Mean eV and CO values significantly increased from 75 min, e′ from 60 min, pV from 75 min, and SV from 15 to 120 min, whereas SVR significantly decreased at 30–60 min in Pimo IM compared to those of Saline IM (P < 0.05). Compared with the Pimo IV, eV and pV were significantly lower at 30–60 min (P < 0.05) while SV was significantly higher at 90–105 min in Pimo IM (P < 0.05). Other hemodynamic parameters (BP, HR, SVR, CO, e′, and E/e′) did not significantly change between Pimo IM and IV.

Conclusions

The hemodynamic effect of pimobendan following IM and IV injection was described. Our results suggested that IM administration of pimobendan is equally comparable and possibly interchangeable with IV administration. This warrant further studies to investigate the clinical effectiveness of IM pimobendan in treating dogs with congestive heart failure or in heart failure cases unable to receive IV or oral administration.

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.

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.

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.

Pharmacodynamics and Pharmacokinetics of Injectable Pimobendan and Its Metabolite, O-Desmethyl-Pimobendan, in Healthy Dogs

Objectives: This study was designed to thoroughly evaluate the effects of bolus pimobendan at a dose of 0.15 mg/kg on cardiac functions, hemodynamics, and electrocardiographic parameters together with the pharmacokinetic profile of pimobendan and its active metabolite, o-desmethyl-pimobendan (ODMP), in anesthetized dogs.

Methods: Nine beagle dogs were anesthetized and instrumented to obtain left ventricular pressures, aortic pressures, cardiac outputs, right atrial pressures, pulmonary arterial pressures, pulmonary capillary wedge pressures, electrocardiograms. After baseline data were collected, dogs were given a single bolus of pimobendan, and the pharmacodynamic parameters were obtained at 10, 20, 30, 60, and 120 min. Meanwhile, the venous blood was collected at baseline and 2, 5, 10, 20, 30, 60, 120, 180, 360, and 1,440 min after administration for the determination of pharmacokinetic parameters.

Results: Compared with baseline measurements, the left ventricular inotropic indices significantly increased in response to intravenous pimobendan, as inferred from the maximum rate of rise in the left ventricular pressure and the contractility index. Conversely, the left ventricular lusitropic parameters significantly decreased, as inferred from the maximum rate of fall in the left ventricular pressure and the left ventricular relaxation time constant. Significant increases were also noted in cardiac output and systolic blood pressure. Decreases were observed in the systemic vascular resistance, pulmonary vascular resistance, left ventricular end-diastolic pressure, pulmonary capillary wedge pressure, right atrial pressure, and pulmonary arterial pressure. The heart rate increased, but the PQ interval decreased. There was no arrhythmia during the observed period (2 h). The mean maximum plasma concentration (in μg/L) for ODMP was 30.0 ± 8.8. Pimobendan exerted large volume of distribution ~9 L/kg.

Conclusions: Intravenous pimobendan at the recommended dose for dogs increased cardiac contraction and cardiac output, accelerated cardiac relaxation but decreased both vascular resistances. These mechanisms support the use of injectable pimobendan in acute heart failure.

Acute Effects of Pimobendan on Cardiac Function in Dogs With Tachycardia Induced Dilated Cardiomyopathy: A Randomized, Placebo-Controlled, Crossover Study

Background: Pimobendan provides a significant survival benefit in dogs with cardiac disease, including degenerative mitral valve disease and dilated cardiomyopathy (DCM). Its positive inotropic effect is well-known, however, it has complex effects and the mechanisms behind the survival benefit are not fully characterized. Secondary hemodynamic effects may decrease mitral regurgitation (MR) in DCM, and the benefits of pimobendan may extend to improved cardiac relaxation and improved atrial function. Hypothesis/Objectives: Our objective was to investigate the acute cardiac effects of pimobendan in dogs with a DCM phenotype. We hypothesized that pimobendan would increase left atrial (LA) contractility, reduce mitral regurgitation, improve diastolic function, and lower circulating NT-ProBNP levels. Animals: Seven purpose-bred Beagles were studied from a research colony with tachycardia induced DCM phenotype. Methods: The effects of pimobendan were studied under a placebo-controlled single-blinded cross-over design. In short, dogs underwent baseline and 3 h post-dose examinations 7 days apart with echocardiography and a blood draw. Dogs were randomized to receive oral placebo or 0.25 mg/kg pimobendan after their baseline exam. Investigators were blinded to treatments until all measurements were compiled. Results: When treated with pimobendan, the dogs had significant increases in systolic function and decreases in MR, compared to when treated with placebo. There were no detectable differences in left atrial measures, including LA size, LA emptying fraction, LA functional index or mitral A wave velocity. Heart rate decreased significantly with pimobendan compared to placebo. There was also a decrease in isovolumetric relaxation time normalized to heart rate. NT-proBNP levels had a high degree of variability. Conclusions: Improved mitral regurgitation severity and improved lusitropic function may contribute to the reported survival benefit for dogs with cardiac disease administered pimobendan. Pimobendan did not overtly improve LA function as assessed by echocardiography, and NT-proBNP was not significantly changed with a single dose of this medication. Further studies are needed to better characterize LA effects with other imaging modalities, to better quantify the total improvement of MR severity, and to assess chronic use of pimobendan on diastolic function in DCM.

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.

Inotropic effects of a single intravenous recommended dose of pimobendan in healthy dogs

We investigated the effects of an injectable pimobendan solution (0.15 mg/kg) on cardiac function in healthy dogs. Fifteen dogs were divided into placebo, intravenous pimobendan injection, and subcutaneous pimobendan injection groups. In the placebo, the heart rate, systolic and end-diastolic left ventricular pressure (LVPs and LVEDP), and peak positive (max dP/dt) and negative (min dP/dt) first derivatives of the left ventricular pressure did not change for 60 min. After the intravenous pimobendan injection, LVEDP decreased significantly within 5 min, while the max dP/dt increased, and the effects continued until 60 min. In comparison, there were no hemodynamic changes after the subcutaneous pimobendan injection. This study demonstrates that injectable pimobendan induced a rapid inotropic effect and decreased the LVEDP in dogs.