Comparison of pharmacodynamic variables following oral versus transdermal administration of atenolol to healthy cats

Investigation of the short-term effects of a transdermal formulation of atenolol in healthy cats

OBJECTIVE

To investigate associations between short-term treatment with a previously described compounded transdermal formulation of atenolol and heart rate in cats.

ANIMALS

11 healthy adult cats.

PROCEDURES

Cats received the atenolol gel formulation (gradually increased from 12.5 mg/cat, q 24 h to 25 mg/cat, q 12 h) by application to the pinnae at home over a 10-day period in a prospective, experimental study. On day 10, cats were hospitalized for measurement of serum atenolol concentrations 3, 6, and 12 hours after the morning treatment. Mean heart rate measured at the 3- and 6-hour time points was compared with a baseline value (measured at enrollment).

RESULTS

All cats completed the study; 4 were excluded from analyses after an apparent formulation error was detected in 1 batch. Two cats had minor adverse effects (localized erythema of the pinna). Five of 7 cats had serum atenolol concentrations ≥ 260 ng/mL (considered therapeutic) at ≥ 1 time point. Heart rate had a strong negative correlation (r = -0.87) with serum atenolol concentration. A 90-day drug stability investigation of 4 formulations (identical to the intended study treatment except for pH [range, 6.5 to 7.7]) revealed an apparent decrease in atenolol concentration at a pH of 7.7.

CONCLUSIONS AND CLINICAL RELEVANCE

Topical administration of the formulation as described resulted in targeted serum atenolol concentrations in most cats, with attendant HR reduction. Validation of these preliminary results in a larger sample and investigation of the treatment in cats with structural heart disease is needed. Verification of appropriate pH (target, 7.0) is likely essential for the compound's stability.

Pharmacokinetics of furosemide after intravenous, oral and transdermal administration to cats

OBJECTIVES

The aim of this study was to determine the pharmacokinetics of furosemide in cats following intravenous (IV), oral and transdermal administration.

METHODS

This study used six healthy adult cats in a three-phase design to compare plasma furosemide concentrations in cats that received one IV 2 mg/kg dose of furosemide, one oral 2 mg/kg dose of furosemide and 3 days of q12h dosing with 2 mg/kg furosemide transdermally applied to the ear pinna.

RESULTS

After IV administration the elimination half-life was (mean and coefficient of variation) 2.25 h (72%), systemic clearance was 149 ml/kg/h (27.4%) and volume of distribution was 227 ml/kg (22%). After oral administration the terminal half-life was 1.2 h (18.7%), peak concentration was 3.4 μg/ml (51.7%) and bioavailability was 48.4%. The transdermal plasma concentrations were undetectable or very low at most time points, and pharmacokinetics were not determined from the transdermal dose.

CONCLUSIONS AND RELEVANCE

Furosemide was rapidly eliminated in cats after oral and IV administration and is probably best administered orally at least q12h in cats with heart failure. The oral dose absorbed was approximately 50%, but the absorption from transdermal administration was negligible.

Evaluation of Transdermal Administration of Phenobarbital in Healthy Cats

The purpose was to determine the safety and achievable serum concentrations of transdermally administered phenobarbital in healthy cats. The hypothesis was that transdermal phenobarbital would achieve therapeutic serum concentrations (15-45 µg/mL) with minimal short-term adverse effects. Enrolled cats had normal physical and neurologic exams and unremarkable bloodwork. Transdermal phenobarbital in a pluronic lecithin organogel-based vehicle was administered at a dosage of 3.0-3.1 mg/kg per ear pinna (total of 6.0-6.2 mg/kg) every 12 hr for 14 days. Serum phenobarbital concentrations were measured 3-6 hr after dosing at seven different times over 15 days. The mean and median serum concentration of phenobarbital at study completion were 5.57 and 4.08 µg/mL, respectively. Mean peak concentration and mean time to peak concentration were 5.94 µg/mL and 13.3 days, respectively. Mild adverse effects were observed. Potency was analyzed in three replicates of the transdermal phenobarbital gel administered; potencies ranged from 62.98 to 82.02%. Transdermal application of phenobarbital in healthy cats achieves a detectable, but subtherapeutic, serum concentration and appears safe in the short term. The use of therapeutic drug monitoring is recommended when this formulation of phenobarbital is used to ensure therapeutic serum concentrations are achieved.

Compounding and Extralabel Use of Drugs in Exotic Animal Medicine

Extralabel drug use is the use of a Food and Drug Administration (FDA)-approved drug in a manner different from what is stipulated on the approved label. Compounding is the process of preparing a medication in a manner not indicated on the label to create a formulation specifically tailored to the needs of an individual patient. Extralabel drug use and compounding are vital aspects of safe and effective drug delivery to patients in exotic animal practice. There are few FDA-approved drugs for exotic animal species, and many approved drugs for other species are not available in suitable formulations for use in exotic animals.

Veterinary Compounding: Regulation, Challenges, and Resources

The spectrum of therapeutic need in veterinary medicine is large, and the availability of approved drug products for all veterinary species and indications is relatively small. For this reason, extemporaneous preparation, or compounding, of drugs is commonly employed to provide veterinary medical therapies. The scope of veterinary compounding is broad and focused primarily on meeting the therapeutic needs of companion animals and not food-producing animals in order to avoid human exposure to drug residues. As beneficial as compounded medical therapies may be to animal patients, these therapies are not without risks, and serious adverse events may occur from poor quality compounds or excipients that are uniquely toxic when administered to a given species. Other challenges in extemporaneous compounding for animals include significant regulatory variation across the global veterinary community, a relative lack of validated compounding formulas for use in animals, and poor adherence by compounders to established compounding standards. The information presented in this article is intended to provide an overview of the current landscape of compounding for animals; a discussion on associated benefits, risks, and challenges; and resources to aid compounders in preparing animal compounds of the highest possible quality.

Effect of atenolol on heart rate, arrhythmias, blood pressure, and dynamic left ventricular outflow tract obstruction in cats with subclinical hypertrophic cardiomyopathy

OBJECTIVE

To investigate the negative chronotropic, antiarrhythmic, and obstruction-relieving effects of atenolol in cats with subclinical hypertrophic cardiomyopathy (HCM).

ANIMALS

Seventeen cats with HCM.

METHODS

Results for echocardiography, electrocardiography, Doppler blood pressure, and 24 h Holter monitoring were compared in cats before and 2-4 weeks after atenolol therapy (6.25-12.5 mg PO q 12 h).

RESULTS

The left ventricular outflow tract maximum velocity (LVOT Vmax) decreased after atenolol administration (mean Vmax pre-treatment 3.3 m/s ± 1.8 m/s; post-treatment 1.6 m/s ± 1.0 m/s, p < 0.0001). Heart rate (HR) decreased after atenolol for all HR modalities. The total number of ventricular origin complexes (TotVent) and ventricular premature complexes (VPCs) decreased after atenolol. The VPCs decreased from a geometric mean of 61 complexes/24 h (range, 11-620 complexes/24 h) to 15 complexes/24 h (range, 1-1625 complexes/24 h) (p < 0.0001). Murmur grade decreased after atenolol from a median grade of 3/6 to 2/6 (p < 0.0001). The systolic blood pressure did not change (mean pre-treatment 130 mmHg ± 16 mmHg, mean post-treatment 123 mmHg ± 20 mmHg, p = 0.2).

CONCLUSION

Atenolol decreases HR, murmur grade, and LVOT obstruction, and to a lesser degree, frequency of ventricular ectopy, in cats with subclinical HCM. Further studies are needed to determine if sudden cardiac death or long-term outcome is influenced by atenolol administration.

Percutaneous absorption of methimazole: an in vitro study of the absorption pharmacokinetics for two different vehicles

The use of transdermal medications in cats has become popular in veterinary medicine due to the ease of administration compared to oral medication. However, the research to support systemic absorption of drugs applied to the pinna after transdermal administration in cats is limited. The aim of this study was to characterize the percutaneous absorption pharmacokinetics of methimazole in a lipophilic vehicle compared to methimazole in Pluronic(®) lecithin organogel (PLO) using a finite dose applied to feline ear skin in an in vitro Franz cell model. The two formulations of methimazole (10 mg) were applied to the inner stratum corneum of six pairs of feline ears. The receptor medium was sampled up to 30 h post-administration, and methimazole concentrations were measured using high-performance liquid chromatography (HPLC). Histological examination of all ears was undertaken as small differences in the thickness of ear skin may have contributed to inter-individual differences in methimazole absorption between six cats. Methimazole was absorbed more completely across the pinnal skin when administered in the lipophilic vehicle compared to administration in the PLO gel (P < 0.001).

Evaluation of a technique to measure heart rate variability in anaesthetised cats

Analysis of heart rate (HR) and heart rate variability (HRV) are powerful tools to investigate cardiac diseases, but current methods, including 24-h Holter monitoring, can be cumbersome and may be compromised by movement artefact. A commercially available data capture and analysis system was used in anaesthetised healthy cats to measure HR and HRV during pharmacological manipulation of HR. Seven healthy cats were subjected to a randomised crossover study design with a 7 day washout period between two treatment groups, placebo and atenolol (1mg/kg, IV), with the efficacy of atenolol to inhibit β1 adrenoreceptors challenged by epinephrine. Statistical significance for the epinephrine challenge was set at P<0.0027 (Holm-Bonferroni correction), whereas a level of significance of P<0.05 was set for other variables. Analysis of the continuous electrocardiography (ECG) recordings showed that epinephrine challenge increased HR in the placebo group (P=0.0003) but not in the atenolol group. The change in HR was greater in the placebo group than in the atenolol group (P=0.0004). Therefore, compared to cats pre-treated with placebo, pre-treatment with atenolol significantly antagonised the tachycardia while not significantly affecting HRV. The increased HR in the placebo group following epinephrine challenge was consistent with a shift of the sympathovagal balance towards a predominantly sympathetic tone. However, the small (but not significant at the critical value) decrease in the normalised high-frequency component (HFnorm) in both groups of cats suggested that epinephrine induced a parasympathetic withdrawal in addition to sympathetic enhancement (increased normalised low frequency component or LFnorm). In conclusion, this model is a highly sensitive and repeatable model to investigate HRV in anaesthetised cats that would be useful in the laboratory setting for short-term investigation of cardiovascular disease and subtle responses to pharmacological agents in this species.

Acceptability and compliance of atenolol tablet, compounded paste and compounded suspension prescribed to healthy cats*

This study was designed to evaluate the cats' acceptance and compliance of the owners and cats towards an extemporaneously prepared palatable compounded atenolol (paste and suspension) formulation in comparison to the commercially obtained tablet, in a randomised, cross-over study design.The three formulations were prescribed twice daily for 6 days to 13 healthy privately-owned cats of 13 different owners, with varying levels of experience in medicating cats. Daily compliance was evaluated via an owner-completed diary, completed after each dose administered. Owner's experience and preference of the formulation was evaluated via questionnaires given prior to, at the end of each treatment protocol, and upon completion of the study. Although compounded suspension was association with fewest missed doses, the majority of cat owners expressed a preference for the divided tablet. Atenolol tablets, compounded paste and suspension acceptance and compliance were comparable. Further work is now required to assess the amount and stability of the active ingredient and the robustness of the paste and suspension formulations prior to any bioavailability comparisons between the formulations.

Pharmacodynamic effects of ivabradine, a negative chronotropic agent, in healthy cats

OBJECTIVE

To determine the pharmacodynamic effects of oral ivabradine in cats.

ANIMALS

Eight healthy, adult domestic short hair cats.

METHODS

Each cat underwent four study periods of 24 h, receiving either one dose of placebo or ivabradine (0.1 mg/kg, 0.3 mg/kg, and 0.5 mg/kg) in a single-blind randomized crossover study. Clinical tolerance was assessed hourly for the first 8 h, at 12 h, and at the end of the 24-h study period. Heart rate and blood pressure were monitored continuously for 18-24 h via radiotelemetry after each treatment. Response to stress (acoustic startle) was studied before (t = 0) and after treatment (t = 4 h). Statistical comparisons were made using a linear mixed models and 1-way and 2-way repeated measures ANOVA.

RESULTS

Heart rate (min(-1)) decreased significantly (P < 0.05) in a dose-dependent manner with peak negative chronotropic effects observed 3 h after ivabradine (mean ± SD; placebo, 144 ± 20; ivabradine 0.1 mg/kg, 133 ± 22; ivabradine 0.3 mg/kg, 112 ± 20; and ivabradine 0.5 mg/kg, 104 ± 11). Heart rate (min(-1)) was still reduced (P < 0.05) 12 h after ivabradine (0.3 mg/kg; 128 ± 18 and 0.5 mg/kg; 124 ± 16) compared to placebo (141 ± 21). The tachycardic response to acoustic startle was significantly (P < 0.01) blunted at all 3 doses of ivabradine. Myocardial oxygen consumption estimated by the rate-pressure product was significantly reduced (P < 0.05) for all doses of ivabradine. No effect of ivabradine on systolic, diastolic, and mean blood pressure was identified and no clinically discernable side effects were observed.

CONCLUSION

These findings indicate that a single oral dose of ivabradine predictably lowers heart rate, blunts the chronotropic response to stress, and is clinically well tolerated in healthy cats. This makes ivabradine potentially interesting in the treatment of feline heart disease where ischemia is of pathophysiologic importance.

Comparison of the effects of ivabradine and atenolol on heart rate and echocardiographic variables of left heart function in healthy cats

BACKGROUND

Ivabradine is a novel negative chronotropic drug used for treatment of ischemic heart disease in people. Little is known about its effects and safety in cats.

HYPOTHESIS/OBJECTIVES

Ivabradine is not inferior to atenolol with regard to clinical tolerance, heart rate (HR) reduction, and effects on cardiac function in healthy, lightly sedated cats.

ANIMALS

Ten healthy laboratory cats.

METHODS

Physical examination, systolic blood pressure measurement, and transthoracic echocardiography were performed in all cats at baseline and after oral administration (4 weeks each) of ivabradine (0.3 mg/kg q12h) and atenolol (6.25 mg/cat q12h; 1.0-1.7 mg/kg) in a prospective, double-blind, randomized, active-control, fully crossed study. A priori noninferiority margins for the effects of ivabradine compared with atenolol were set at 50% (f = 0.5) based on predicted clinical relevance, observer measurement variability, and in agreement with FDA guidelines. Variables were compared by use of 2-way repeated measures ANOVA.

RESULTS

Ivabradine was clinically well tolerated with no adverse events observed. HR (ivabradine, P < .001; atenolol, P < .001; ivabradine versus atenolol, P = .721) and rate-pressure product (RPP) (ivabradine, P < .001; atenolol, P = .001; ivabradine versus atenolol, P = .847) were not different between treatments. At the dosages used, ivabradine demonstrated more favorable effects than atenolol on echocardiographic indices of left ventricular (LV) systolic and diastolic function and left atrial performance.

CONCLUSIONS AND CLINICAL IMPORTANCE

Ivabradine is not inferior to atenolol with regard to effects on HR, RPP, LV function, left atrial performance, and clinical tolerance. Clinical studies in cats with hypertrophic cardiomyopathy are needed to validate these findings.