Table 4:

Common antiepileptic drugs used in idiopathic epilepsy

DrugMechanism action Advantage Potential adverse effects / disadvantage
ImepitoinLow-affinity partial agonist of benzodiazepine site GABA receptor and affects calcium channels
  • Less severe adverse effects

  • No tolerance

  • No dependence

  • Steady state in three days

  • No requirement to monitor serum concentration

Polyphagia
Hyperactivity
Polyuria
Polydipsia
Somnolence
May not be as effective AED as phenobarbital
Liver metabolised
PhenobarbitalAgonist GABA also affects glutamate receptor, calcium channels and voltage-dependant potassium currents
  • Most effective AED

  • Controls epilepsy in ∼50 per cent patients and 33.5 per cent improved

Dose related /transientIdiosyncratic
Somnolence /sedation
Polyuria
Polydipsia
Polyphagia
Ataxia
Hepatotoxicity
Idiosyncratic
Anxiety
Acute hepatotoxicity
Blood dyscrasia
Hypoalbuminaemia
Superficial necrolytic dermatitis (hepatocutaneous syndrome)
Liver metabolised
Tolerance
Dependence
BromideNegative ion thought to hyperpolarise neurons by passing through the neuronal chloride channels
  • No liver metabolism

  • Once daily dosing

  • Synergistic with phenobarbital?

Dose relatedIdiosyncratic
Somnolence /sedation
Polyuria
Polydipsia
Polyphagia
Diarrhoea
Ataxia
Gastrointestinal irritation
Pancreatitis
Panniculitis
Neuromuscular signs, including megaoesophagus
Not as effective AED as phenobarbital
Steady state in three to four months
Excretion affected by dietary salt
Levetiracetum*Novel mechanism of action. Binds synaptic vesicle protein SV2A, which modulates synaptic vesicle exocytosis and neurotransmitter release
  • Less severe adverse effects

  • No liver metabolism

  • Neuroprotective

Dose relatedIdiosyncratic
Somnolence /sedationNone reported
Clearance enhanced by phenobarbital
Most dogs require TID therapy (some QID)
Used in combination, ie, ‘add on’ (in refractory epilepsy)
Possible honeymoon effect
Zonisamide*Affects sodium and calcium ion channels
  • Potential as monotherapy

  • Neuroprotective

Dose related /transientIdiosyncratic
Sedation
Ataxia
Vomiting
Acute hepatotoxicity
Expensive
Clearance enhanced by phenobarbital
Better not in combination phenobarbital?
Possible honeymoon effect
  • * Not licensed for canine epilepsy

  • Tolerance: loss of anticonvulsant efficacy during prolonged treatment; Dependence: withdrawal signs observed on termination of long-term treatment; Honeymoon effect: initial positive response lost within 12 months

  • AED Anti-epileptic drug, QID Dosing every six hours, TID Dosing every eight hours