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