Topiramate

This is licensed as an add-on treatment for refactory partial epilepsy, with or without secondary generalisation not satisfactorily controlled with other antiepileptic medication.

Topiramate is also indicated for the treatment of seizures associated with Lennox-Gastaut syndrome and primary generalised tonic-clonic seizures.

Topiramate has a triple action involving attenuation of neuronal excitation, enhancement of GABA-mediated inhibition, and blockade of sodium channels.

Carbamazepine and phenytoin induce its metabolism, reducing topiramate levels by about 40% (1).

Topiramate should be introduced slowly e.g. 25 mg daily in adults, increasing by increments of 25 mg each week or two) in order to avoid side effects. Generally the maintenance dose is 200-600mg (2).

Side effects include: sedation, impaired concentration, dizziness and paraesthesias. Weight loss and anorexia may occur. There have been reports of renal calculi in patients treated with topiramate - patients should be encouraged to maintain an adequate fluid intake (2). Also there have been reports of an ocular syndrome associated with the use of topiramate (3) - see linked item.

There is also evidence that oral topiramate, when used in adults with alcohol dependence, was effective for reducing drinking, promoting abstinence, and decreasing craving as an adjunct to standardised medication compliance management (4).

The summary of drug characteristics should be consulted before prescribing this drug.

Reference:

1. Prescribers' Journal (1998), 38(2), 98-106.
2. Prescriber (2000), 11 (23), 45-55.
3. Janssen-Cilag Ltd (15/10/2001). Letter - Important Safety Information - Topamax (R) Tablets and Topamax (R) Sprinkle Capsules (Topiramate).
4. Johnson BA et al. Oral topiramate for treatment of alcohol dependence: a randomised controlled trial. Lancet 2003;361:1677-85.