REDUCING PHENOBARBITAL DOSAGES

W. B. Thomas, DVM

Protocols vary depending on the specific circumstances, including blood levels, degree of seizure control, side effects and the individual veterinarian's preferences.  Ask three neurologists and you will probably get three different answers.

In general, I usually decrease the phenobarbital dose once the bromide level reaches 150 mg/dL.  This usually takes about one month of treatment with bromide, unless a loading dose is used. For dogs on bromide and phenobarbital, I usually aim for a phenobarbital level of about 25 mcg/ml.  If there are no seizures after 6 months of combination therapy, I often try to decrease the phenobarbital further.  For dogs that are to be maintained on bromide alone, I usually aim for a higher bromide level (about 200 mg/dL).

How quickly you decrease the phenobarbital depends on the specific circumstances. Remember that if you change the dose of phenobarbital it takes about 10 to 14 days for the blood level to equalize at the new level. If the dog has minimal side effects, I usually decrease the phenobarbital by about 20% and wait a month or two to monitor for seizures.  If there are none, then repeat.

In some cases it is desirable to decrease the phenobarbital faster.  An example would include a dog with substantial side effects (wobbly gait, lethargy) or liver failure.  Frequent monitoring of blood levels during withdrawal is very helpful in these cases.

Again, these are general comments that are intended to help people understand this complicated subject.  In no way are they intended to replace direct veterinary supervision, which is critical whenever the dose of anti-seizure drugs is adjusted.