A seizure is an abnormal and unregulated electrical discharge occurring in the brain. This leads to a transient interruption in brain function, manifested by reduced alertness, abnormal sensations, and focal involuntary movements or convulsions. Several types of seizures exist, with common types including tonic-clonic seizures and partial onset seizures.

The exact mechanisms by which topiramate exerts pharmacological actions on seizures and migraines are currently not fully characterized. Several properties of this drug, however, are likely to contribute to its therapeutic effects. Topiramate has been observed to exert actions on voltage-dependent sodium channels, GABA receptors, and glutamate receptors.

Topiramate stimulates GABA-A receptor activity at brain non-benzodiazepine receptor sites and reduces glutamate activity at both AMPA and kainate receptors. Normally, GABA-A receptors are inhibitory and glutaminergic receptors are stimulatory for neuronal activity. By increasing GABA activity and inhibiting glutamate activity, topiramate blocks neuronal excitability, preventing seizures and migraines. Additionally, it blocks the voltage-dependent sodium channels, further blocking seizure activity. Topiramate has been shown to inhibit various carbonic anhydrase isozymes, but the clinical significance of this is unknown at this time.

Epilepsy: Topiramate is indicated as monotherapy in adults and children aged 6 years and above with newly diagnosed epilepsy who have generalised tonic-clonic seizures or partial seizures with or without secondarily generalised seizures. Topiramate is indicated as adjunctive therapy for adults and children over 2 years of age who are inadequately controlled on conventional first line antiepileptic drugs for partial seizures with or without secondarily generalised seizures; seizures associated with Lennox Gastaut Syndrome and primary generalised tonic-clonic seizures.

Migraine: Topiramate is indicated in adults for the prophylaxis of migraine headache. Prophylactic treatment of migraine may be considered in situations such as: adults experiencing three or more migraine attacks per month; frequent migraine attacks that significantly interfere with the patient's daily routine. Continuing therapy should be reviewed every six months.

Epilepsy: Monotherapy:

• Adults and children over 16 years: Titration should begin at 25 mg nightly for 1 week. The dosage should then be increased at 1- or 2-week intervals by increments of 25 or 59 mg/day, administered in two divided doses. The recommended initial target dose for topiramate monotherapy in adults with newly diagnosed epilepsy is 100 mg/day and the maximum recommended daily dose is 400 mg.
• Children aged 6-16 years: Treatment of children aged 6 years and above should begin at 0.5 to 1 mg/kg nightly for the first week. The dosage should then be increased at 1- or 2-week intervals by increments of 0.5 to 1 mg/kg/day, administered in two divided doses. The recommended initial target dose range for topiramate monotherapy in children with newly diagnosed epilepsy aged 6 years and above is 3 to 6 mg/kg/day. Higher doses have been tolerated and rarely doses up to 16 mg/kg/day have been given.

Epilepsy: Adjunctive therapy:

• Adults and children over 16 years: The minimal effective dose as adjunctive therapy is 200 mg per day. The usual total daily dose is 200 mg to 400 mg in two divided doses. Some patients may require doses up to 800 mg per day, which is the maximum recommended dose.
• Children aged 2-16 years: The recommended total daily dose of Topiramate as adjunctive therapy is approximately 5 to 9 mg/kg/day in two divided doses. Titration should begin at 25 mg nightly for the first week. The dosage should then be increased at 1- or 2-week intervals by increments of 1 to 3 mg/kg/day (administered in two divided doses), to achieve optimal clinical response. Dose titration should be guided by clinical outcome. Daily doses up to 30 mg/kg/day have been studied and were generally well tolerated.

Migraine:

• Adults and children over 16 years: Titration should begin at 25 mg nightly for 1-week. The dosage should then be increased in increments of 25 mg/day administered at 1-week intervals. The recommended total daily dose of topiramate as treatment for the prophylaxis of migraine headache is 100 mg/day administered in two divided doses. Some patients may experience a benefit at a total daily dose of 50 mg/day.
• Children: Topiramate in migraine prophylaxis has not been studied in children under 16 years.

Hypersensitivity to any component of this product.

Nausea, abdominal pain, dyspepsia, diarrhoea, dry mouth, taste disturbance, weight loss, anorexia, paraesthesia, hypoaesthesia, headache, fatigue, dizziness, speech disorder, drowsiness, insomnia, impaired memory & concentration, anxiety, depression, visual disturbance, lesscommonly: sucidal ideation, rarely: reduced sweetening mainly children, metabolic acidosis and alopecia, very rarely: Leucopenia, thrombocytopenia and serious skin reaction.

Overdose Effects

Topiramate overdose can result in severe metabolic acidosis. In acute topiramate overdose, if the ingestion is recent, the stomach should be emptied immediately by lavage or by induction of emesis. Activated charcoal has been shown to adsorb topiramate in vitro. Treatment should be appropriately supportive. Haemodialysis has been shown to be an effective means of removing topiramate from the body. The patient should be well hydrated.

In patients with or without a history of seizures or epilepsy, antiepileptic drugs, including topiramate, should be gradually withdrawn to minimize the potential for seizures or increased seizure frequency. Topiramate can produce central nervous system-related adverse events and may be more sedative than other antiepileptic drugs. Drowsiness is a likelihood. In addition, there have been reports of visual disturbances/blurred vision. Patients should be warned of these and advised that if affected, they should not drive, operate machinery and/or take part in activities where such reactions could put themselves or others at risk.

Pregnancy & Lactation

Topiramate should not be used during pregnancy unless, in the opinion of the physician, the potential benefit outweighs the potential risk to the foetus. Topiramate should not be used during breastfeeding.