Peer-reviewed veterinary case report
Phenobarbitone side effects in epileptic cats and how common they are
By Marsh, Oliver et al.·Published in Journal of feline medicine and surgery·2021·Neurology and Neurosurgery Service, United Kingdom·View original on PubMed →
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Original publication title: Prevalence and clinical characteristics of phenobarbitone-associated adverse effects in epileptic cats.
- Species:
- cat
Plain-English summary
A group of 77 cats with epilepsy was treated with phenobarbitone, a common medication for seizures, and about 47% experienced side effects. The most common issues included sedation and ataxia (loss of coordination), which often appeared within the first month of treatment. In one case, a cat developed a serious but rare reaction that caused low white blood cell counts, which resolved after stopping the medication. Adjusting the dosage or adding another seizure medication increased the chances of side effects. Most cats were able to tolerate the medication after the initial adjustment period.
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Abstract
OBJECTIVES: The study objective was to investigate the prevalence and clinical characteristics of phenobarbitone-associated adverse effects in epileptic cats. METHODS: The medical records of two veterinary referral clinics from 2007 to 2017 were searched for cats fulfilling the inclusion criteria of a diagnosis of epilepsy, treatment with phenobarbitone and available follow-up information on the occurrence of adverse effects. Follow-up information was obtained from the medical records of the primary veterinarian and referral institutions and a questionnaire completed by the cats' owners. RESULTS: Seventy-seven cats met the inclusion criteria. Fifty-eight were affected by idiopathic epilepsy and 19 by structural epilepsy. One or more of the following adverse effects were reported in 47% of the cats: sedation (89%); ataxia (53%); polyphagia (22%); polydipsia (6%); polyuria (6%); and anorexia (6%). Logistic regression analyses revealed significant associations between adverse effect occurrence and both phenobarbitone starting dosage and administration of a second antiepileptic drug (AED). For each 1 mg/kg q12h increment of phenobarbitone, the likelihood of adverse effects increased 3.1 times. When a second AED was used, the likelihood of adverse effects increased 3.2 times. No association was identified between epilepsy aetiology and adverse effect occurrence. An idiosyncratic adverse effect, characterised by severe neutropenia and granulocytic hypoplasia, was diagnosed in one cat. This resolved following phenobarbitone discontinuation. CONCLUSIONS AND RELEVANCE: The prevalence of phenobarbitone-associated adverse effects was 47%. Sedation and ataxia were most common. These are type A adverse effects and are predictable from phenobarbitone's known pharmacological properties. In the majority of cases, adverse effects occurred within the first month of treatment and were transient. Idiosyncratic (type B) adverse effects, which were not anticipated given the known properties of the drug, occurred in one cat. Increased phenobarbitone starting dosage and the addition of a second AED were significantly associated with the occurrence of adverse effects.
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Search related cases →Original publication on PubMed: https://pubmed.ncbi.nlm.nih.gov/32484071/