Disposition and safety of zonisamide after intravenous and oral single dose and oral multiple dosing in normal hound dogs

Immune-mediated polyarthritis and anterior uveitis secondary to zonisamide administration in a dog with refractory epilepsy

The objective of this article is to describe a case of suspected zonisamide-induced immune-mediated polyarthritis (IMPA) and anterior uveitis in a dog. A 7-year-old male neutered Siberian Husky with a history of refractory idiopathic epilepsy was presented for cluster seizures. Following the addition of zonisamide to the antiepileptic regime, the dog developed new IMPA and anterior uveitis. Within a few weeks of discontinuation of the zonisamide, the dog's IMPA and anterior uveitis resolved. These immune-mediated conditions were thus presumed to be an idiosyncratic reaction to zonisamide. To our knowledge, this is the first report of IMPA and anterior uveitis in dogs associated with zonisamide administration at its recommended dose.

Thyroid function tests during nonthyroidal illness syndrome and recovery in acutely ill dogs

BACKGROUND

Nonthyroidal illness syndrome (NTIS) can result in thyroid function test alterations that mimic hypothyroidism. The duration of NTIS-induced changes in dogs is not well-described.

OBJECTIVES

Document alterations in thyroid function tests during NTIS and recovery, and the time necessary for their resolution.

ANIMALS

From 103 dogs sampled, 25 euthyroid dogs with acute, resolvable illness having a low serum total thyroxine (TT4) concentration on admission were analyzed.

METHODS

Prospective observational study. Serum TT4 concentration was measured in 103 dogs within 4 hours of admission. If below the reference interval (RI), subsequent serum samples were obtained every 24 hours from admission until discharge (acute phase) and at 2 weeks and 4 weeks after discharge (recovery phase). Serum samples were submitted for batch measurement of serum TT4, free thyroxine (fT4), total 3,5,3'-triiodothyronine (TT3), and thyroid-stimulating hormone (TSH) concentrations.

RESULTS

In the cohort of dogs analyzed, serum TT4, TT3, and fT4 concentrations were below the RI in 100%, 80%, and 16% at admission; 20%, 80%, and 0% at discharge; 4%, 8%, and 0% at 2 weeks; and 0%, 0%, and 0% at 4 weeks, respectively. Serum TSH concentration was within the RI in 100% at admission and discharge, and above the RI in 4% and 12% at 2 weeks and 4 weeks, respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

Naturally occurring NTIS in dogs induces alterations in thyroid function tests during acute illness and recovery. Measurement of serum TT4 concentration 2 to 4 weeks after discharge or serum fT4 concentration by ED during illness is recommended for accurate assessment of thyroid function in acutely ill dogs.

The efficacy and safety of cannabidiol as adjunct treatment for drug-resistant idiopathic epilepsy in 51 dogs: A double-blinded crossover study

BACKGROUND

Approximately 30% of dogs with idiopathic epilepsy (IE) are drug-resistant. Recent studies have suggested cannabidiol (CBD) may be an effective anticonvulsant in dogs with IE.

OBJECTIVE

To evaluate the addition of CBD to antiseizure drugs (ASDs) on seizure frequency and to report adverse events in dogs with drug-resistant IE.

ANIMALS

Fifty-one dogs. Dogs having at least 2 seizures per month while receiving at least 1 ASD were included in the trial.

METHODS

Double-blinded placebo-controlled crossover study. The 5 mg/kg/day dosage met futility requirements after 12 dogs, and a dosage of 9 mg/kg/day was used in the next 39 dogs. Dogs were randomly assigned to receive CBD or placebo for 3 months, with a 1-month washout period between oils. Total numbers of seizures and seizure days were recorded. Diagnostic testing was performed periodically throughout the trial.

RESULTS

At the 9 mg/kg/day dose, the decrease in total seizure frequency was significant compared with placebo. A 24.1% decrease in seizure days occurred in dogs receiving CBD and a 5.8% increase occurred in dogs receiving placebo (P ≤ .05). No significant difference was found in the number of responders (≥50% decrease in total seizures or seizure days). Liver enzyme activities increased at both dosages. Decreased appetite and vomiting were more common in the CBD phase (P ≤ .05).

CONCLUSIONS AND CLINICAL IMPORTANCE

Cannabidiol decreased total seizures and seizure days compared to placebo when administered to dogs PO at 9 mg/kg/day. Liver enzymes should be monitored with administration of CBD in dogs.

Influence of medications on thyroid function in dogs: An update

Erroneous thyroid function test results can occur because of drugs that alter thyroid hormone physiology in one or more aspects, including synthesis, secretion, distribution, and metabolism. Research since publication of the last review in the Journal of Veterinary Internal Medicine (JVIM) 20 years ago has evaluated the effects of amiodarone, zonisamide, inhalant anesthetics, clomipramine, trilostane, and toceranib on thyroid function tests in the dog. In addition, recent work on the effects of glucocorticoids, sulfonamides, phenobarbital, and nonsteroidal anti-inflammatory drugs will be reviewed. Awareness of these effects is necessary to avoid misdiagnosis of hypothyroidism and unnecessary treatment.

Presumed zonisamide-induced blood dyscrasias in four dogs

OBJECTIVE

To describe 4 canine cases of presumed zonisamide-induced blood dyscrasias.

CASE SUMMARY

From 2007 to 2018 at Angell Animal Medical Center and from 2014 to 2019 at the Cummings School of Veterinary Medicine at Tufts University, 4 dogs presented with febrile neutropenia while being administered zonisamide. No septic focus was found on workup for any of the dogs, and the clinical signs were attributed to an idiosyncratic drug reaction. All WBC counts returned to normal with drug withdrawal, and all dogs survived.

NEW OR UNIQUE INFORMATION PROVIDED

Presumptive zonisamide-induced blood dyscrasias are a rare complication that has not previously been reported in the veterinary literature.

Abnormal Behavior Episodes Associated With Zonisamide in Three Dogs: A Case Report

Psychiatric adverse effect associated with anti-seizure drugs has been well-recognized in human medicine. This case report describes three dogs with presumptive idiopathic epilepsy presented for abnormal behavior episodes. Abnormal behavior episodes included sudden rage and aggression to the family members, insomnia, restlessness, and/or constant attention-seeking behavior. MRI study and cerebrospinal fluid analysis in two dogs were unremarkable. The abnormal behavior episodes deteriorated along with gradual dose increment of zonisamide and these episodes almost completely disappeared within 5 days after discontinuation of zonisamide. The exact same episodes relapsed within days after re-administration of zonisamide and disappeared again shortly after discontinuation of zonisamide. Dose adjustments of other anti-seizure medications in case 2 did not result in significant changes in these behavior episodes. Although psychiatric adverse effects including aggressive behavior associated with zonisamide are widely recognized in humans, this is the first report in dogs in the clinical setting.

Pharmacokinetics of zonisamide after oral single dosing and multiple-dose escalation administration in domestic chickens (Gallus gallus)

Background

There are few effective drugs for treatment of seizures in avian species.

Objectives

To investigate the pharmacokinetics and safety of zonisamide in chickens.

Methods

Phase 1: chickens (n = 4) received a single oral dose of zonisamide at 20 mg/kg. Blood samples were collected intermittently for 36 hr after dosing. Phase 2: chickens (n = 8) received zonisamide in a dose escalation protocol (20, 30, 60 and 80 mg/kg orally every 12 hr). The dose was increased weekly, and peak and trough blood samples were collected on Days 1, 3, and 7 each week. Two birds were randomly euthanized at the end of each week. Plasma zonisamide concentrations were analysed using a commercial immunoassay. Drug concentration vs. time data were subjected to non‐compartmental pharmacokinetic analysis.

Results

For Phase 1, peak plasma zonisamide (C_max) was 15 ± 3 µg/ml at 2 ± 1 hr (T_max). The disappearance half‐life was 6.5 ± 1 hr. Mean plasma concentrations remained within the (human) therapeutic range (10–40 µg/ml) for 6 hr. For Phase 2 of the study, plasma concentrations of zonisamide remained within or close to the recommended mammalian therapeutic range for birds in the 20 and 30 mg/kg dose. Area under the curve (AUC) and C_max were dose dependent. Two birds developed immune‐mediated haemolytic anaemia.

Conclusions

Zonisamide appears to be a viable drug for use in chickens at a dose of 20 mg/kg orally every 12 hr.

Efficacy of zonisamide on interictal electroencephalography in familial spontaneous epileptic cats

Objectives The effectiveness of zonisamide (ZNS) against spontaneous epilepsy in cats has not yet been described. The purpose of this study was to investigate the effect of ZNS on interictal paroxysmal discharges (PDs) using scalp electroencephalography (EEG) in familial spontaneous epileptic cats (FSECs). Methods Eight FSECs were evaluated (six males and two females). Scalp EEG measurements were performed once a week for 3 weeks before ZNS administration (Pre-ZNS). Thereafter, administration of ZNS was started and an adjustment period was instituted until the drug in plasma achieved the steady state. When ZNS in plasma was confirmed to be within 10-40 μg/ml, scalp EEG measurements were performed once a week for 3 weeks (Post-ZNS). The number of PDs (counts/min) were compared between Pre-ZNS and Post-ZNS treatment. Results The median number of PDs for Pre-ZNS and Post-ZNS were 0.43/min (0.13-0.82/min) and 0.28/min (0.07-0.87/min), respectively. The number of PDs Post-ZNS was significantly reduced compared with Pre-ZNS ( P = 0.02). Conclusions and relevance This study showed that ZNS, within the recommended therapeutic range suggested for use in humans and dogs (10-40 µg/ml), reduced the number of PDs recorded on EEG in FSECs that are considered a model for cats with idiopathic epilepsy. Although phenobarbital is the antiepileptic drug of choice for epileptic cats, the results of this research provide evidence to support the use of ZNS in cats with phenobarbital-resistant epilepsy or for cats that cannot use phenobarbital due to adverse side effects.

Antiepileptic drugs' tolerability and safety--a systematic review and meta-analysis of adverse effects in dogs

Background

The safety profile of anti-epileptic drugs (AEDs) is an important consideration for the regulatory bodies, owners and prescribing clinicians. Information on their adverse effects still remains limited. A systematic review including a meta-analytic approach was designed to evaluate existing evidence for the safety profile of AEDs in canine patients. Electronic searches of PubMed, CAB Direct and Google scholar were carried out without date or language restrictions. Conference proceedings were also searched. Peer-reviewed full-length studies reporting adverse effects of AEDs in epileptic and healthy non-epileptic dogs were included. Studies were allocated to three groups based on their design. Individual studies were evaluated based on the quality of evidence (study design, study group sizes, subject enrolment quality and overall risk of bias) and the outcome measures reported (proportion of specific adverse effects for each AED, prevalence and 95 % confidence interval of the affected population in each study and comparative odds ratio of adverse effects for AEDs).

Results

Ninety studies, including six conference proceedings, reporting clinical outcomes of AEDs’ adverse effects were identified. Few studies were designed as blinded randomised controlled clinical trials. Many studies included low canine populations with unclear criteria of subject enrolment and short treatment periods. Direct comparisons suggested that imepitoin and levetiracetam might have a better safety profile than phenobarbital, whilst the latter might have a better safety profile than potassium bromide. However, none of these comparisons showed a statistically significant difference. Comparisons between other AEDs were not possible as a considerable amount of studies lacked power calculations or adequate data to allow further statistical analysis. Individual AED assessments indicated that levetiracetam might be one of the safest AEDs, followed by imepitoin and then phenobarbital and potassium bromide; these findings were all supported by a strong level of evidence. The safety profile in other AEDs was variable, but weak evidence was found to permit firm conclusions or to compare their safety to other AEDs.

Conclusions

This systematic review provides objective evaluation of the most commonly used AEDs’ adverse effects. Adverse effects usually appeared mild in all AEDs and subsided once doses and/or serum levels were monitored or after the AED was withdrawn. Although phenobarbital might be less safe than imepitoin and levetiracetam, there was insufficient evidence to classify it as an AED with a high risk of major adverse effects. It is important for clinicians to evaluate both AEDs’ effectiveness and safety on an individual basis before the selection of the appropriate monotherapy or adjunctive AED therapy.

2015 ACVIM Small Animal Consensus Statement on Seizure Management in Dogs

This report represents a scientific and working clinical consensus statement on seizure management in dogs based on current literature and clinical expertise. The goal was to establish guidelines for a predetermined, concise, and logical sequential approach to chronic seizure management starting with seizure identification and diagnosis (not included in this report), reviewing decision‐making, treatment strategies, focusing on issues related to chronic antiepileptic drug treatment response and monitoring, and guidelines to enhance patient response and quality of life. Ultimately, we hope to provide a foundation for ongoing and future clinical epilepsy research in veterinary medicine.

International Veterinary Epilepsy Task Force consensus proposal: medical treatment of canine epilepsy in Europe

In Europe, the number of antiepileptic drugs (AEDs) licensed for dogs has grown considerably over the last years. Nevertheless, the same questions remain, which include, 1) when to start treatment, 2) which drug is best used initially, 3) which adjunctive AED can be advised if treatment with the initial drug is unsatisfactory, and 4) when treatment changes should be considered. In this consensus proposal, an overview is given on the aim of AED treatment, when to start long-term treatment in canine epilepsy and which veterinary AEDs are currently in use for dogs. The consensus proposal for drug treatment protocols, 1) is based on current published evidence-based literature, 2) considers the current legal framework of the cascade regulation for the prescription of veterinary drugs in Europe, and 3) reflects the authors' experience. With this paper it is aimed to provide a consensus for the management of canine idiopathic epilepsy. Furthermore, for the management of structural epilepsy AEDs are inevitable in addition to treating the underlying cause, if possible.

Erythema multiforme associated with zonisamide in a dog

This report describes a dog that developed erythema multiforme in temporal association with administration of the sulphonamide-based anticonvulsant drug zonisamide. Similar adverse drug reactions have been associated with sulphonamide antimicrobial drugs. Caution should be exercised when prescribing this medication for dogs with known hypersensitivity to sulphonamides.

Antiepileptic drug therapy and monitoring

Over the past 2 decades, the number of antiepileptic drugs (AEDs) available to veterinarians has grown exponentially. Coupled with this increase is the ability to rapidly and accurately diagnose underlying brain disease with readily accessible magnetic resonance imaging. As a result, the veterinary community is attuned to the need for early treatment intervention. As more treatment choices become available, the unrelenting questions still arise are when should treatment begin, which initial drug therapy is best for our patients, when should treatment changes be considered, and finally, what are the advantages that newer drugs provide for our patients. The purpose of this chapter is to review decision-making strategies for AED therapy, provide an overview of the applicability of current AED available, and present information on the therapeutic advances in epilepsy.

A simple and accurate liquid chromatography-tandem mass spectrometry method for quantification of zonisamide in plasma and its application to a pharmacokinetic study

Zonisamide (ZNM) is an antiepileptic drug that is used as an adjunctive therapy in the treatment of adults with partial seizures. An LC-MS/MS method for quantification of ZNM in human and rabbit plasma using (2)H4,(15)N-Zonisamide as an internal standard (IS) has been developed and validated. The drug and IS were extracted by ether and analyzed on Symmetry(®) C18 column. Quantitation was achieved using ESI-interface employing MRM mode. The method was validated over the concentration range of 0.5-50μg/mL and 0.5-30μg/mL (r(2)>0.99) in human and rabbit plasma samples, respectively. Intra- and inter-run precision of ZNM assay in human and rabbit plasma samples ranged from 0.8 to 8.5% with accuracy (bias) varied from -11.3 to 14.4% indicating good precision and accuracy. Stability of ZNM in human and rabbit plasma samples at various conditions showed that the drug was stable under the studied conditions. Analytical recoveries of ZNM and IS from spiked human and rabbit plasma samples were in the range of 70.8-77.3% and 85.6-110.4%, respectively. Matrix effect study showed a lack of matrix effect on mass ions of ZNM and IS. The developed method was successfully applied for a pharmacokinetic study by measuring ZNM in rabbit plasma samples. Moreover, the method is routinely utilized for TDM of ZNM.

Characteristics of selected second-generation antiepileptic drugs used in dogs

A significant number of cases of clinical canine epilepsy remain difficult to control in spite of the applied treatment. At the same time, the range of antiepileptic drugs is increasingly wide, which allows efficient treatment. In the present paper we describe the pharmacodynamics and pharmacokinetics of the newer antiepileptic drugs which were licensed after 1990 but are still not widely used in veterinary medicine. The pharmacokinetic profiles of six of these drugs were tested on dogs. The results of experimental studies suggest that second generation antiepileptic drugs may be applied in mono- as well as in poli- treatment of canine epilepsy because of the larger safety margin and more advantageous pharmacokinetic parameters. Knowledge of the drugs' pharmacokinetics allows its proper clinical appliance, which, in turn, gives the chance to improve the efficiency of pharmacotherapy of canine epilepsy.

Possible drug-induced hepatopathy in a dog receiving zonisamide monotherapy for treatment of cryptogenic epilepsy

A 9-year old female spayed Rottweiler was diagnosed with cryptogenic epilepsy and started on zonisamide monotherapy (8.3 mg/kg, PO, q 12 hr). Three weeks after the 1st dose of zonisamide the dog presented for vomiting, inappetence and icterus. Serum biochemistry showed marked elevation of liver enzymes, consistent with hepatocellular damage and cholestasis. No underlying cause for liver disease was identified and a drug-induced hepatopathy was suspected. Zonisamide was discontinued and replaced by potassium bromide. Supportive therapy consisted of intravenous fluids, antiemetics, antibiotics and hepatoprotectants. The dog made a complete recovery and serial serum biochemical examinations showed complete normalisation of liver parameters 8 weeks after discontinuation of zonisamide. Based on a human Drug-induced Liver Injury Diagnostic Scale, the likelihood for zonisamide-induced hepatopathy was classified as "possible". Veterinary practitioners and owners should be educated about the potential for an idiosyncratic drug reaction to zonisamide. If signs of hepatotoxicity are recognised early and zonisamide is discontinued, complete recovery is possible.