Topiramate was developed as an antiepileptic and is used alone or as adjunctive treatment in generalised tonic-clonic seizures.

MOA

There appear to be multiple mechanisms of action:

• blocks voltage-gated Na+ channels
• increases GABA action
• carbonic anhydrase inhibition: this results in a decrease in urinary citrate excretion and formation of alkaline urine that favours the creation of calcium phosphate stone

Topiramate is an inducer of the P450 enzyme CYP3A4. This may result in hormonal contraception being less effective. As a result, the Faculty of Sexual and Reproductive Health (FSRH) suggests the following for patients taking topiramate:

• combined oral contraceptive pill and progestogen-only pill: UKMEC 3 (disadvantages outweigh advantages):
• implant: UKMEC 2 (advantages generally outweigh the disadvantages)
• The injection (Depo-Provera) and intrauterine system are not affected by topiramate.

Adverse effects

• reduced appetite and weight loss (make it useful in IIH)
• dizziness
• paraesthesia
• lethargy and poor concentration
• rare but important: acute myopia and secondary angle-closure glaucoma

Topiramate is associated with a risk of foetal malformations.

should not be used in women and girls of childbearing potential unless conditions of the Pregnancy Prevention Programme are fulfilled.