Does switching brands matter? Complications associated with switching between phenobarbital brands in two dogs with idiopathic epilepsy

Switching between brands of the same antiseizure medication has been associated with a loss of epileptic seizure control in people. No such reports are available in the veterinary literature. Here, we describe two cases in which client-owned dogs with idiopathic epilepsy experienced complications following phenobarbital brand switch, despite no change in the administered dosage. Both dogs had been on treatment with oral phenobarbital for at least 23 months without complications. Following brand switching, one dog became markedly sedated, ataxic and anorexic, and the other dog experienced severe cluster seizures. The measured serum phenobarbital concentrations were significantly altered from the previously measured pre-brand switching concentrations. Echoing what has been described in human medicine, these cases suggest that therapeutic complications can occur when switching phenobarbital brand in chronically treated dogs with idiopathic epilepsy. Such complications should be considered when modulating antiseizure treatment in dogs. The exact cause for the resulting complications is unclear.