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Phenobarbital – a beneficial eight-hourly dosing option?
  1. Annette Wessmann, DrMedVet, DipECVN, PGCertAcPrac, FHEA, MRCVS
  1. Pride Veterinary Centre, Riverside Road, Derby DE24 8HX, UK; e-mail:

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IDIOPATHIC epilepsy is the most common neurological medical condition in dogs with an estimated prevalence of 0.6 per cent presenting to first-opinion practice in the UK (Kearsley-Fleet and others 2013). About two-thirds of dogs with idiopathic epilepsy are controlled with one or a combination of two medications. Phenobarbital remains the most commonly used first-line antiepileptic drug in dogs affected by idiopathic epilepsy, and achieves sufficient seizure control in about two-thirds of affected dogs when used as a single agent (Packer and others 2015, Tipold and others 2015). The phenobarbital doses used in individual epileptic dogs are largely modified based on the seizure frequency, phenobarbital serum levels and the drug side effects. Drug formularies generally advise a 12-hourly phenobarbital oral dosing regime (Plumb 2008, Ramsey 2014). This is based on the reported elimination half-life in dogs ranging from 12 to 125 hours, with an average of approximately two days. Oral phenobarbital (5-ethyl-5-phenylbarbituric acid) is absorbed within two hours after administration. Healthy dogs reached peak levels of phenobarbital in 3.8 and 4.6 hours when receiving 5.5 mg/kg orally once and 5.5 mg/kg/every 24 hours for …

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