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 re sponses, 2) impairment of AMPA/kainate glutamate receptors and 3) supp ression 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 pharma cokinetic drug interactions. However, topiramate. can reduce the estro gen component of oral contraceptive medications. Women may require bir th control preparations containing 50 mu g of estrogen. Topiramate cle arance is reduced in severe renal failure and increased by enzyme-indu cing antiepileptic drugs. The dose of topiramate may have to be reduce d in renal failure or when withdrawing enzyme inducers.