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