Topiramate

Question 1

What dose is topiramate started at and titrated up to according to the BNF?

Answer 1

• Start at 25mg at night for 1 week.
• Increase in 25mg steps weekly.
• Usual dose is 50-100mg a day in 2 divided doses.

Question 2

What is the pharmacological action of topiramate?

Answer 2

It is an enzyme inducer of the P450 enzyme CYP34.

Question 3

Because it is an enzyme inducer, what do FSRH (Faculty of Sexual and Reproductive Health) recommend?

Answer 3

• AEDs (phenytoin, carbamazepine, barbiturates, primidone, topiramate, oxcarbazepine) that induce liver enzymes may reduce the contraceptive efficacy of combined contraceptive methods, progestogen-only pills and progestogen-only implants.
• Therefore POP and COCP are UKMEC 3. (Disadvantages outweigh the advantages)
• Implant is UKMEC 2.
• IUS, IUD and Depo-provera are all UKMEC 1 and aren’t affected by AED.

Question 4

Topiramate was originally developed as an antiepileptic & enzyme inducer and thus can effect hormonal contraceptives. What other AEDs can also do this?

Answer 4

• Phenytoin
• Carbamazepine
• Barbiturates
• Primidone
• Topiramate
• Oxcarbazepine

Question 5

What are some adverse side effects of topiramate?

Answer 5

• weight loss
• dizziness
• paraesthesia
• lethargy and poor concentration
• rare but important: acute myopia and secondary angle closure glaucoma