| GENERIC NAME: topiramate
BRAND NAME: Topamax
DRUG CLASS AND MECHANISM: Topiramate is an oral drug
that is used to prevent the seizures of epilepsy. (It is an anti-epileptic
or anti-seizure drug). It is used primarily among patients who are not
controlled by other anti-epileptic drugs. About 1 in 4 Americans diagnosed
with epilepsy has seizures that resist treatment with other anti-epileptic
drugs. Topiramate also prevents migraine headaches.
Seizures are due to the abnormal activity ("firing") of nerves
in the brain, and the abnormal activity spreads to smaller or larger portions
of the brain. Although topiramate's exact mechanism of action is unknown,
scientific studies suggest that it may alter neurotransmitters within
the brain. Neurotransmitters are chemicals that nerves manufacture and
use to communicate with other nearby nerves. By altering the production
or action of the neurotransmitters, topiramate may suppress the abnormal
activity of the nerves in the brain that cause the seizures or may prevent
the abnormal activity from spreading to other nerves. Other studies suggest
that topiramate may suppress the nerves directly (i.e., not by altering
neurotransmitters) and make them less likely to fire. The FDA approved
topiramate as a tablet in 1997. The Sprinkle Capsules were approved in
October, 1998.
PREPARATIONS: Tablets (25, 100 and 200 mg) and Sprinkle
Capsules (15 and 25 mg)
STORAGE: Topiramate tablets should be stored at room
temperature, 59-86°F (15-30 ° C). Sprinkle capsules should be
stored at or below 77 ° F (25 °C).
PRESCRIBED FOR: Seizures may be classified as either
partial if they involve only a small portion of the brain or generalized
if they involve more of the brain. Topiramate is used in combination with
other anti-seizure drugs among adults and children aged 2-16 years with
partial seizures or generalized tonic-clonic seizures (in which there
is prolonged contraction of the muscles of the body that causes rigidity
as well as jerking motions). It also is used in patients two years of
age and older with seizures associated with the Lennox-Gastaut Syndrome,
a severe form of epilepsy which accounts for up to 10 percent of all cases
of childhood epilepsy. Children with Lennox-Gastaut Syndrome experience
delays in their development and up to dozens of different, mixed types
of seizures a day. The most common types of seizures in this syndrome
are tonic (stiffening of the body, with the eyes rolling upwards, dilation
of the pupils and shallow, irregular breathing), atonic (brief loss of
muscle tone and consciousness, causing abrupt falls), myoclonic (sudden
muscle jerks), and absence (staring spells).
Topiramate also is approved for the prevention of migraine headaches
in adults.
DOSING: Most commonly, topiramate is started in low
doses, 25 or 50 mg per day, and then increased slowly, under a doctor's
orders, by 25 to 50 mg per week until an effective daily dose is reached.
This slow approach to treatment reduces side effects.
In children, the starting dose is up to 25 mg (1 to 3 mg/kg/day), taken
nightly for the first week. The dose is then increased at 1 or 2 week
intervals by 1 to 3 mg/kg/day.
Although the usual adult dose is 200 mg twice daily, some adult patients
may begin to see a clinical response at 200 mg per day. Some patients
need doses higher than 200 mg daily. In children, the usual dose is 2.5
to 4.5 mg/kg twice daily.
Patients should maintain an adequate fluid intake in order to minimize
the risk of kidney stones.
DRUG INTERACTIONS: The following medications, when taken
with topiramate, increase the risk of kidney stones: acetazolamide (Diamox),
dorzolamide (Trusopt), methazolamide (Neptazane), dichlorphenamide (Daranide).
Carbamazepine (Tegretol) and phenytoin (Dilantin) markedly decrease the
amount of topiramate in the body by increasing its elimination from the
body. As a result, topiramate may lose effectiveness unless doses are
increased.
Topiramate may decrease the amount of estrogen in the body in women taking
oral contraceptives, possibly increasing the chances of unwanted pregnancy.
Patients with seizure disorders taking anticonvulsant medications, including
topiramate, may develop nerve toxicity from a chemical, 4'-O-methylpyridoxine,
found as a contaminant in some ginkgo preparations.
PREGNANCY: Topiramate has been associated with abnormalities
of the fetus (teratogenicity) in experimental animal studies. No data
on fetal effects of topiramate exists in humans.
NURSING MOTHERS: Topiramate is excreted in the milk
of lactating rats. It is not known whether topiramate is excreted in human
milk or if it has important effects on nursing infants.
SIDE EFFECTS: In adults, the most common side effects
of topiramate are tiredness, dizziness, coordination problems, speech
problems, changes in vision or double vision, difficulty with memory,
and sensory distortion.
In children, the most common side effects are drowsiness, tiredness,
loss of appetite, nervousness, difficulty with concentration/attention,
weight decrease, aggressive reaction and difficulty with memory.
Since topiramate was approved, there have been 23 cases reported (as
of 8-17-01) of a sudden onset of vision and eye problems. Symptoms have
typically occurred within the first month of therapy, with patients reporting
an acute onset of decreased vision and/or eye pain. Eye examination revealed
myopia (nearsightedness), redness, decreased depth of the anterior chamber
of the eye and elevated ocular pressure, with or without dilation of the
pupils. Fluid accumulation within the eye may displace the lens and iris
anteriorly causing secondary angle closure glaucoma. If patients develop
this syndrome, the treatment is to discontinue topiramate as rapidly as
possible, according to the judgment of the treating physician.
Caution! Before starting
to take this medicine, it is vital that you should consult your doctor!
Do not use it on your own initiative, without medical advice.
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