Medications and Drugs

Pharmacy Author: Emmanuel Saltiel, Pharm.D.
Medical/Pharmacy Editor: Jay W. Marks, M.D.

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.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets: 25, 100 and 200 mg. 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). Topiramate sprinkle capsules are approved for treatment without other drugs in patients 10 years of age and older.  Topiramate 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.

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