Canine Epilepsy Website

Phenobarbitone
Therapeutic and toxic effects of phenobarbitone are related to serum concentrations and not the quantity of drug administered orally. Therapeutic monitoring of serum phenobarbitone concentration can be helpful in determining the optimal dose.

*Monitoring should be performed:*
•	When steady state blood levels are reached after starting treatment or after changing oral dosage (12 to 15 days in dogs). This provides a baseline to guide further changes in doses according to clinical circumstances.
•	If seizure frequency increases.
•	Every 3 to 6 months to verify that blood concentrations are maintained in the therapeutic range.
•	If drug-related side effects are suspected.
•	If drugs are added that might interfere with phenobarbitone’s pharmacokinetics (corticosteroids, cimetidine, chloramphenicol).

Recommended therapeutic range in dogs is 20 to 35 ug/ml (65-194µmol/l). Most dogs will “respond” (reduction in frequency, intensity and severity of the seizures with minimal side effects) when the serum level of phenobarbitone is within this range. However, some dogs might need to be in the upper limit of this range while others might need to be below the lower limit.

This therapeutic range is only an indication of changes required in the oral dosage.

Monitoring of serum bromide concentration should be performed:
•	When steady state blood levels are reached after starting treatment or after changing oral dosage (3 to 6 months in dogs). This provides a baseline to guide further changes in doses according to clinical circumstances.
•	If seizure frequency increases.
•	Every 6 to 12 months to verify that blood concentrations are maintained in the therapeutic range.
•	If drug-related side effects are suspected.

Recommended oral dosage in dogs is 30 mg/kg once daily. Therapeutic serum concentrations are 880 to 3000 mg/ml as a solitary agent and 810 to 2400 mg/ml in combination with phenobarbitone.

Dyer KR, Shell LG (1993) Anticonvulsant therapy: a practical guide to medical management of epilepsy in pets. Vet Med 88, 647-653.