A multicenter prospective evaluation of owner medication adherence for feline cardiovascular disease in the referral setting.

OBJECTIVE: The aim of this paper is to evaluate owners' chronic medication adherence for management of feline cardiovascular disease in the small animal referral setting. ANIMALS, MATERIALS AND METHODS: A questionnaire-based study of owners at five multispecialty, small animal referral centers was conducted. Owners completed a written survey evaluating demographics, degree of medication adherence, and difficulties encountered for medication adherence. Owners were free to decline participation in the study. RESULTS: Fifty-four questionnaires were available for review. The most common diagnosis was hypertrophic cardiomyopathy (n = 31, 57.4%). Clopidogrel was the most cited medication that was difficult to administer consistently (n = 13, 24.0%) although twenty owners (37.0%) reported no difficulty consistently administering medications. "Taste of medication" (n = 14, 25.9%) was the most reported reason for difficulty medicating their cat, and most owners (n = 36, 66.7%) stated twice daily was the highest frequency of heart medications they feel they can consistently administer. Fifty owners (92.6%) met the criteria for medication adherence. CONCLUSIONS: Chronic medication adherence in this study population was high. Clopidogrel was the most difficult medication to consistently administer, and twice a day dosing was the highest frequency of medication administration most owners could achieve. Cardiologists should be aware of these factors when determining optimal treatment protocols for the management of cardiovascular disease in cats.

Two-dimensional, long-axis echocardiographic ratios for assessment of left atrial and ventricular size in dogs.

INTRODUCTION: Left ventricular (LV) and left atrial (LA) enlargement affect management and outcome of dogs with cardiac disease. Short-axis, two-dimensional echocardiographic (2DE) images, indexed to the aorta (Ao), are frequently used to identify cardiomegaly. Long-axis images offer complementary views of the left heart. ANIMALS: Eighty healthy dogs and 25 dogs with MMVD. METHODS: Healthy dogs were prospectively recruited to determine reference intervals (Clinical Laboratory Standards Institute methodology) for long-axis ratios. Measurement variability and repeatability were quantified by intraclass correlation coefficient and coefficient of variation. Mean long-axis ratios from dogs with MMVD were compared with healthy dogs (unpaired t-test). In addition, the proportion of MMVD dogs exceeding the 97.5 percentile by LV/Ao and a conventional, allometric method were compared (McNemar's test). RESULTS: Two-dimensional echocardiographic long-axis reference intervals were as follows: left ventricular to aortic dimension (LV/Ao) 1.8-2.5; left atrial to aortic dimension (LA/Ao) 1.8-2.4, and left atrial to left ventricular dimension (LA/LV) 0.9-1.1. Intraobserver and interobserver measurement agreement was good-to-excellent (intraclass correlation coefficients ≥0.84), and day-to-day variability was low (coefficient of variations <4%). Left ventricular to aortic dimension, LA/Ao, and LA/LV were significantly greater in canine MMVD compared with healthy dogs (p<0.001). The percentages of MMVD dogs demonstrating LV dilatation by LV/Ao and conventional method were 68% and 36%, respectively (p=0.043, 95% confidence interval for difference 7.9%, 56.1%). CONCLUSIONS: Simple 2DE long-axis ratios of LV/Ao, LA/Ao, and LA/LV are repeatable and demonstrate clinical utility for identifying LV and LA enlargement in dogs with MMVD.

Echocardiographic Estimates of Right Ventricular Systolic Function in Dogs with Myxomatous Mitral Valve Disease.

BACKGROUND: Right ventricular (RV) dysfunction independently predicts outcomes in human myxomatous mitral valve disease (MMVD). There is limited information regarding RV systolic function in dogs with MMVD. HYPOTHESIS: Right ventricular systolic function differs among stages of disease, decreasing in decompensated MMVD. ANIMALS: Thirty-sixclient-owned dogs with MMVD not receiving oral cardiovascular medications. METHODS: Prospective clinical study. Dogs were categorized according to disease severity as ACVIM Stage B1, B2, or C. Seven echocardiographic indices of RV systolic function were measured. Groups were compared by 1-way ANOVA and Tukey's HSD test. Frequencies of cases with cardiac remodeling falling outside previously established reference intervals were compared using Fisher's exact test. Intra- and interobserver measurement variability was calculated for each RV function index. RESULTS: The indices TAPSE (P = 0.029), RV StL (P = 0.012), and RV StRL (P = 0.041) were significantly different between groups. A greater proportion of B2 dogs (7 of 12) had TAPSE values above reference intervals compared with B1 (2 of 12) or C (2 of 12) dogs (P = 0.027). Measurement variability of TAPSE, RV S', and RV StG was clinically acceptable. CONCLUSIONS AND CLINICAL IMPORTANCE: Right ventricular systolic function differs between stages of MMVD, increasing in stage B2, and declining in stage C. The prognostic importance of RV function indices, particularly TAPSE, might be worth evaluating in dogs with MMVD.

Interventional Closure of a Patent Ductus Arteriosus Using an Amplatz Canine Duct Occluder in an Alpaca Cria.

A 6-month old female alpaca cria presented to The Ohio State University for evaluation of a cardiac murmur. Echocardiography revealed a left-to-right shunting patent ductus arteriosus, a restrictive left-to-right shunting perimembranous ventricular septal defect, and secondary moderate left atrial and ventricular dilation. Aortic root angiography demonstrated a type IIA patent ductus arteriosus (PDA). Interventional closure of the PDA was successfully performed, without complication, using an Amplatz canine duct occluder. This case report describes the materials and methods used for interventional closure of a PDA in an alpaca cria.

Unilateral absence of an external jugular vein in two English bulldogs with pulmonary valve stenosis.

Two English bulldogs referred for interventional palliation of severe pulmonary valve stenosis were incidentally diagnosed with unilateral absence of an external jugular vein (left in one case, right in the other) by computed tomography and Doppler ultrasound. The right internal jugular vein also could not be visualized in the dog with absence of the left external jugular vein. Cervical venous anomalies can impact diagnostic or interventional venous catheterization procedures such as balloon pulmonary valvuloplasty. Additionally, absence of an external jugular vein may impact central venous catheter placement. Absence of an external jugular vein should be considered in dogs when the external jugular vein cannot be easily palpated. Ultrasound or computed tomography may help identify jugular venous anatomy and confirm anomalies.

Dependence of hydrogen peroxide formation in rat liver microsomes on the molecular structure of cytochrome P-450 substrates: a study with barbiturates and beta-adrenoceptor antagonists.

In the present study, the molecular structure of xenobiotics has been successfully linked to their effect on the oxidase activity of cytochrome P-450, determined as microsomal hydrogen peroxide formation. A homologous series of 5-alkyl-5-ethyl barbiturates and a heterologous series of beta-adrenoceptor antagonists was used. The logarithm of the rate of microsomal hydrogen peroxide formation could be correlated with the logarithm of the apparent partition (n-octanol/buffer) coefficient for the barbiturate derivatives according to a parabolic function. The statistics of the correlation improved considerably by applying a bilinear model in order to fit the data. This probably indicates that both transport of the substrate to cytochrome P-450 and interaction with hydrophobic substrate binding sites of cytochrome P-450 are involved in the modulating effect of substrates on the oxidase function of cytochrome P-450. With the series of beta-adrenoceptor antagonists no clear-cut structure activity relationship with regard to the oxidase activity was apparent at first sight. However, when the inhibitory effect of the beta-antagonists on the 'cytochrome P-450 metabolic intermediate (MI) complex' formation that occurs during the microsomal biotransformation of 33 microM tofenacine was studied a relationship with the lipophilicity could be demonstrated. It is known that MI complex formation occurs with specific subforms of cytochrome P-450. By using this inhibitory activity of the beta-adrenoceptor antagonists, the interaction of the compounds becomes restricted to these specific subforms of cytochrome P-450. In both the oxidase activity as well as the MI complex formation phenobarbital induced cytochrome P-450 is involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of rat hepatic microsomal lipid peroxidation by mesna via glutathione.

Glutathione (GSH, 1 mmol/l) inhibits Fe2+/ascorbic acid induced liver microsomal lipid peroxidation. Oxidized GSH (GSSG, 1 mmol/l) did not affect rate or extent of lipid peroxidation. The inhibition by GSH seems specific since the sulfhydryl agent sodium 2-mercaptoethanesulfonate (mesna) gave a slight stimulation of lipid peroxidation. This stimulation is probably explained by a reduction by mesna of dehydroascorbic acid which is formed during the incubation, into ascorbic acid. Remarkably, mesna (1 mmol/l) added together with GSSG (1 mmol/l) produced the same inhibition as with 1 mmol/l GSH alone. This can be explained by direct reduction of GSSG to GSH by mesna. This is corroborated in experiments in which GSH is measured directly. Dimesna did not show an effect on lipid peroxidation. In the protective action of mesna against reactive substances its ability to reduce GSSG should be appreciated.

Inhibition of diazepam metabolism in microsomal- and perfused liver preparations of the rat by desmethyldiazepam, N-methyloxazepam and oxazepam.

Hydroxylated metabolites of diazepam can be conjugated and are therefore generally thought not to affect the metabolism of diazepam. Liver microsomes, obtained from phenobarbital-pretreated rats, showed an inhibition of diazepam (10(-5) M) metabolism by desmethyldiazepam as well as by N-methyloxazepam or oxazepam (5 X 10(-5) M). In a single-pass perfusion of the rat liver an inhibition of diazepam disposition by exogenously administered desmethyldiazepam and by hydroxylated diazepam metabolites was also demonstrated. No oxazepam glucuronides were found after oxazepam infusion. However, infusion with N-methyloxazepam resulted in large amounts of oxazepam-glucuronides. The results indicate that administration of N-demethylated as well as hydroxylated metabolites may result in inhibition of the metabolism of their precursor. If hydroxylated metabolites are formed in situ they become more easily conjugated in comparison with administered hydroxylated metabolites and are therefore less effective as inhibitor.

Relationship between molecular structure and cytochrome P450-metabolic intermediate complex formation, studied with orphenadrine analogues.

Complexation of ferrous cytochrome P450 by metabolic intermediates formed during NADPH-catalyzed metabolism of compounds structurally related to orphenadrine was studied. This so-called metabolic intermediate complexation was determined in rat liver microsomes, obtained from phenobarbital-pretreated rats, at 455 nm using 33 microM of the orphenadrine derivatives. Using secondary amine derivatives with various N-alkyl substituents, a parabolic relationship between the logarithm of percentage of cytochrome P450 complexation and hydrophobic fragmental constant was observed. The derivative with a bulky tertiary butyl group, however, was devoid of metabolic intermediate-complexing activity. This indicates that steric factors besides lipid solubility may govern the complexing activity; also substitution at the phenyl group affects metabolic intermediate complex formation.

Inhibition of mono-oxygenase and oxidase activity of rat-hepatic cytochrome P-450 by H2-receptor blockers.

Of four H2 blockers, cimetidine, tiotidine, oxmetidine and ranitidine, all except ranitidine showed ligand (type II) interactions with oxidized cytochrome P-450. High- and low-affinity binding sites were observed in hepatic microsomes of control, phenobarbital (PB)-treated and 3-methylcholanthrene (3-MC)-treated rats. All H2 blockers except for ranitidine (up to 400 microM) produced a concentration-dependent inhibitory effect of the metabolic intermediate (MI)-cytochrome P-450 complex formation which is displayed during metabolism of tofenacine in PB hepatic microsomes in vitro. At 400 microM, of all H2 blockers only oxmetidine was able to dissociate in vitro the isosafrole metabolite-cytochrome P-450 complex formed in vivo. Endogenous NADPH-dependent microsomal H2O2 production is inhibited in control, PB and 3-MC microsomes by the H2 blockers to various extents. In liver microsomes of phenobarbital-pretreated rats, substrate-dependent inhibition of H2O2 production correlates with inhibition of MI-cytochrome P-450 complex formation of tofenacine. Moreover, the magnitude of ligand (type II) binding of the H2 blockers correlates with inhibition of H2O2 formation. This indicates that prevention of oxygen activation by ligand binding decreases endogenous H2O2 production. Inhibition of both mono-oxygenase as well as oxidase activity of cytochrome P-450 may lead to adverse drug interactions. On the other hand formation of reactive or deleterious intermediates formed as a consequence of cytochrome P-450 activities can be prevented.

Effect of multiple administration of orphenadrine or mono-N-desmethylorphenadrine on cytochrome P-450 catalyzed reactions in the rat.

Multiple administration (i.p.) of orphenadrine or its mono-N-demethylated metabolite, tofenacine (day 1, 20 mg/kg; day 2-5, 30 mg/kg) results in a considerable induction (50%) of the total cytochrome P-450 content. In addition, approximately 6% of the total amount of cytochrome P-450 was found to be blocked by a metabolic intermediate, formed from orphenadrine or tofenacine. Induction is apparent in enhancing the in vitro N-demethylation of aminopyrine and ethylmorphine and the p-hydroxylation of aniline. Pretreatment induced orphenadrine metabolism in vitro. The metabolism of tofenacine, however, was reduced. Probably this is due to a specific inhibition caused by the irreversible interaction of the metabolic intermediate with cytochrome P-450. In vivo, no induction of the aminopyrine metabolism (30 mg/kg, i.v.) is apparent, i.e., no change in the clearance was observed after pretreatment. This is probably due to the presence of relatively high, inhibitory concentrations of tofenacine (in the vicinity of cytochrome P-450). These results show that during chronic administration of orphenadrine or tofenacine, the in vivo disposition of concomitantly ingested compounds is determined by the influence of induction, high substrate and/or metabolite levels and complexation of cytochrome P-450. Moreover, based on these results an hypothesis is put forward in order to explain the phenomenon of product inhibition, which has been suggested to occur in man under chronic orphenadrine dosing conditions.

Product inhibition in orphenadrine metabolism as a result of a stable cytochrome P-450-metabolic intermediate complex formed during the disposition of mono-N-desmethylorphenadrine (tofenacine) in the rat.

Product inhibition is thought to be involved in unexpected accumulation of orphenadrine, which occurs during chronic medication with this anti-Parkinson drug in man. In previous studies (Biochem. Pharmacol. 31, 2745-2753 (1982) we established the formation of reactive metabolic intermediates (MI) during metabolism of orphenadrine and its mono-N-demethylated metabolite tofenacine, which may block cytochrome P-450 (MI-complex). In this study we investigated the role of MI-complexation in product inhibition. Three different assays were used to establish the amount of cytochrome P-450 involved in MI-complexation, which was induced by tofenacine (30 mg/kg i.p.) in phenobarbital pretreated rats. If liver microsomes were prepared 3 hours after tofenacine injection, both spectral titration of oxidized cytochrome P-450, determination of loss of metyrapone binding sites at reduced cytochrome P-450 as well as ferricyanide oxidation of the MI-complex revealed 8-13% complexation of cytochrome P-450. Our data also suggest that MI-complexation is generated on phenobarbital induced cytochrome P-450 species. Phenobarbital induction was also shown to activate orphenadrine metabolism in vitro. Moreover, with a newly developed capillary GLC method, using nitrogen detection, we showed inhibition of orphenadrine- and tofenacine metabolism in vitro, by MI-complexation. This study therefore showed that MI-complexation may produce product inhibition.

Cytochrome P450 oxidase activity and its role in NADPH dependent lipid peroxidation.

A comparison is made between microsomal NADPH-dependent H2O2 production and malondialdehyde (MDA) formation in rat liver microsomes, obtained from phenobarbital pretreated rats. An increase in H2O2 formation was observed during NADPH-dependent disposition (10 min) of 100 microM diazepam (33%) and 2 mM hexobarbital (69%). In contrast orphenadrine (100 microM) and its mono-N-demethylated metabolite tofenacine (100 microM) decreased the H2O2 formation (35% and 55%, respectively). However, all these substrates were found to inhibit NADPH-dependent lipid peroxidation (60 min), estimated by measuring MDA formation, to various extents. These data strongly suggest that the oxidase activity of cytochrome P450 (H2O2 production) is not involved in a rate-limiting step in NADPH-dependent lipid peroxidation.

Sex differences in the kinetic constants of ethylmorphine demethylation and type I binding to hepatic microsomal cytochrome P-450 in mice. The influence of castration and testosterone.

1. In the CPB-SE mouse strain sex differences were observed in the Km and Vmax of ethylmorphine demethylation and in the deltaAmax of its type I binding to cytochrome P-450. In the CPB-V strain a small sex difference in the Vmax of the demethylation was found, whereas Ks and deltaAmax of type I binding differed considerably. 2. Testosterone pre-treatment of female CPB-SE mice abolished all sex differences, as did castration of males, except in Vmax, which was partially decreased. In the CPB-V strain testosterone pre-treatment of females abolished sex differences in type I binding, but had no effect on ethylmorphine demethylation. 3. Km values exceeded the corresponding Ks in all cases and sex differences in deltaAmax far exceeded those in Vmax. It is concluded that the Km is determined not only by the Ks of type I binding and the reduction rate of the type I complex between ethylmorphine and cytochrome P-450. The larger sex differences in deltaAmax as compared with Vmax may be attributable to type I binding of ethylmorphine to cytochrome P-450 subspecies not involved in its demethylation.