For oral administration.
The required dosage will differ to some extent between individuals and with the nature and severity of the disorder.
Tablets must be given at the same time each day and should be co-ordinated with feeding times in a consistent manner to optimise treatment success.
Dogs should be dosed orally, starting with a dose of 2-5mg per kg bodyweight per day. The dose should be divided and administered twice daily.
Steady state serum concentrations are not reached until 1-2 weeks after treatment is initiated. The full effect of the medication does not appear for two weeks and doses should not be increased during this time.
If seizures are not being controlled, the dosage may be increased by 20% at a time, with associated monitoring of serum phenobarbital levels. The phenobarbital serum concentration may be checked after steady state has been achieved, and if it is less than 15µg/ml the dose may be adjusted accordingly. If seizures recur the dose may be raised up to a maximum serum concentration of 45µg/ml. High plasma concentrations may be associated with hepatotoxicity. Blood samples could be taken at the same time to allow plasma phenobarbital concentration to be determined preferably during trough levels, shortly before the next dose of phenobarbital is due.
Plasma concentrations should be interpreted in conjunction with the observed response to therapy and a full clinical assessment including monitoring for evidence of toxic effects in each animal.
Clinical data suggests that considerable variation in plasma concentrations of phenobarbital may be observed in some animals. This variation may result in an animal with a trough plasma concentration of phenobarbital below the typical minimum therapeutic level and a peak plasma concentration approaching the maximum level. If the seizure control is inadequate in such animals, care should be taken when increasing the dose as toxic levels may be reached or exceeded. Peak and trough plasma concentrations of phenobarbital may need to be measured in such animals. (Peak plasma concentrations are reached within approximately 3 hours after administration).
If the seizures are not being satisfactorily controlled and if the maximum plasma concentration of phenobarbital is about 40µg/ml, then the diagnosis should be reconsidered and/or a second antiepileptic product (such as bromides) should be added to the treatment protocol.
Tablets can be divided into equal halves or quarters to ensure accurate dosing.
To break a cross scored tablet into quarters, place the tablet on an even surface with the scored side up and apply pressure on the middle with your thumb.
To break a tablet into two halves, place the tablet on an even surface with the scored side up, hold one half of the tablet and press down on the other half.