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. 


WB Thomas DVM
Dipl. ACVIM (Neurology)
University of Tennessee



 

REDUCING PHENOBARBITAL (PB) DOSAGES

By Guardian Angel Marianne & Sage

 

All of us whose dogs take Phenobarbital (Pb) would love to reduce the dosage down to nothing.  A reality check, however, tells us that our dogs need help to control their seizures, and Pb offers that help.  With the good, can come the bad, and sometimes the side effects of medications like Pb outweigh the benefits and a reduction of the Pb dosage is in order.

Sometimes we are reducing the Pb dosage while introducing another anti-seizure drug, such as Potassium Bromide (KBr);other times we are hoping to simply get by on a lower Pb dosage.  Reasons for reducing Pb dosages include: incontinence, liver distress, ataxia, agitation and lethargy.

Whether you are weaning your dog off Pb entirely, or simply trying to get down to a lower dosage, it's extremely important to follow veterinary guidelines for the safety of your pup.

When my epi-dog, Sage, became incontinent a few months after beginning Pb, I met with my vet to discuss the possibility of lowering her dosage.  Most vets will want the dog to be seizure-free for at least a year, some want the dog seizure-free for two years before discussing the possibility of lowering a dosage.  Sage had not had a seizure since we had begun Pb treatment, but that had been only seven months prior.  Still, because her seizures were relatively mild, and she had good control, we decided to try to reduce her Pb and see what happened.

Because Pb is in the Barbiturate family, dogs develop a dependency on the drug.  When it is reduced abruptly, this in itself can cause a seizure.  My vet and I decided to reduce Sage's Pb 10% every three weeks.  This was based on the information that the body takes two weeks to adjust to different Pb dosages, and that Sage's seizure cycle was once every two to three weeks.

It is difficult to cut down such a small pill as Pb, so I recommend buying a pill cutter at your local drug store.  Many times the small amount of Pb I cut off would go zinging across my kitchen when I used only a knife, and I would end up on my hands and knees searching for it.  A pill cutter is much easier and more accurate to use.

I think the best way to cut down the pill is to first cut it in half, then into quarters.  To reduce by 10%, gauge where half of 25% is and take off a bit less than that.

It's tricky to judge where to cut if you simply start from the edge of the pill.  Keep in mind that the pill is thickest in the middle, and it's cylindrical, so judging 10% is especially difficult.

For some dogs, especially those with liver distress, the Pb must be reduced very quickly.  Follow your vet's advice and monitor your pup closely.

With the reduction of Sage's Pb, her incontinence stopped.  She did reach a point where she had a seizure, so we knew that we could go no farther in her reduction plan.  Sage will always take Pb to control her seizures, but we
are very grateful that she can get by on a low dosage, and that her incontinence is in the past.

Some vets are very cavalier about reducing Pb, but we urge you to show caution and patience because sometimes the seizures can come back with a vengeance and you may never regain the control you once had. Happily, this is not always the case, but as most epi-parents have probably learned by now, one never knows when dealing with seizures.



References:

Dr. W. Jean Dodds, DVM; James M. Griffin, MD and Liisa D. Carlson, DVM, Dog Owner's Home

Veterinary Handbook, 3rd Edition, NY: 2000; Kate A. W. Roby, VMD, Lenny Southam, DVM, The Pill Book Guide to Medication for your Dog and Cat, NY: 1998