💊 Topiramate

Topiramate is an antiepileptic drug, often referred to as a broad-spectrum anticonvulsant. It is also used in the prophylaxis of migraine.

Topiramate has multiple mechanisms of action. It blocks voltage-gated sodium channels, enhances GABAergic activity by modulating GABA-A receptors, and antagonises AMPA/kainate glutamate receptors. It also weakly inhibits carbonic anhydrase.

Topiramate is indicated for the treatment of focal (partial) seizures and primary generalised tonic-clonic seizures, either as monotherapy or adjunctive therapy. It is also approved for Lennox-Gastaut syndrome. Furthermore, it is a first-line agent for the prophylaxis of migraine headaches in adults.

Absolute contraindications include hypersensitivity to topiramate or any of its excipients. It is also contraindicated in pregnancy due to teratogenicity, particularly in the first trimester. Caution is needed in patients with a history of kidney stones due to its carbonic anhydrase inhibition.

Common adverse effects include paraesthesia, fatigue, dizziness, somnolence, and cognitive impairment (e.g., 'topiramate fog' or word-finding difficulties). Weight loss is also a frequent side effect. Serious but less common adverse effects include acute myopia with secondary angle-closure glaucoma, metabolic acidosis, and kidney stones.

Renal function should be monitored, especially in patients with pre-existing renal impairment. Bicarbonate levels should be checked periodically due to the risk of metabolic acidosis. Intraocular pressure should be monitored if visual symptoms develop. Weight should also be monitored.

When prescribing, always check for pregnancy status and counsel on effective contraception due to teratogenicity. Be aware of potential drug interactions, particularly with oral contraceptives (reducing their efficacy) and other enzyme-inducing antiepileptics. Counselling should cover the importance of adequate hydration to reduce kidney stone risk, and to report any visual disturbances immediately.

Topiramate is known for its significant cognitive side effects, often described as 'topiramate fog', which can impact patient adherence. It is a carbonic anhydrase inhibitor, contributing to the risk of metabolic acidosis and kidney stones. Its teratogenic potential means careful counselling on contraception is essential for women of childbearing potential.

SBAs frequently test knowledge of topiramate's cognitive side effects, such as word-finding difficulties, and its association with weight loss. Questions might also focus on the risk of kidney stones or the rare but serious side effect of acute angle-closure glaucoma. Its teratogenicity is another high-yield topic.