Topiramate: pharmacokinetics and pharmacodynamics

Topiramate is a structurally novel anti-epileptic drug with at least 3 postulated mechanisms of action including: 1) potentiation of GABA responses, 2) impairment of AMPA/kainate glutamate receptors and 3) suppression of high frequency action potential firing. It has a favourable pharmacokinetic profile with rapid absorption, good bio-availability, linear pharmacokinetics, relatively long half-life and limited pharmacokinetic drug interactions. However, topiramate can reduce the estrogen component of oral contraceptive medications. Women may require birth control preparations containing 50 micrograms of estrogen. Topiramate clearance is reduced in severe renal failure and increased by enzyme-inducing anti-epileptic drugs. The dose of topiramate may have to be reduced in renal failure or when withdrawing enzyme inducers.