Topiramate increases brain GABA, homocarnosine, and pyrrolidinone in patients with epilepsy

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Abstract
Objective: To measure the effects of topiramate on brain gamma-aminobutyric acid (GABA) in patients with epilepsy. Background: Topiramate is a new antiepileptic medication with multiple putative mechanisms of action. In a recent meta-analysis of the newer antiepileptic drugs, topiramate was the most potent. Homocarnosine and pyrrolidinone are important metabolites of GABA with antiepileptic actions. Methods: In vivo measurements of GABA, homocarnosine, and pyrrolidinone were made of a 14-cm3 volume in the occipital cortex using 1H spectroscopy with a 2.1-Tesla magnetic resonance spectrometer and an 8-cm surface coil. Twelve patients (eight women) with refractory complex partial seizures were studied while using topiramate. Nine epilepsy-free, drug-free volunteers served as control subjects. Results: Topiramate increased mean brain GABA, homocarnosine, and pyrrolidinone concentrations in all patients. In paired measurements, brain GABA increased by 0.7 μmol/g (SD 0.3, n 7, 95% CI 0.4 to 1.0, p < 0.01). Homocarnosine increased by 0.5 μmol/g (SD 0.2, n 7, 95% CI 0.3 to 0.7, p < 0.001). Pyrrolidinone increased by 0.21 μmol/g (SD 0.06, n 7, 95% CI 0.16 to 0.27, p < 0.01). In two additional patients, GABA, homocarnosine, and pyrrolidinone increased after they were switched from vigabatrin to topiramate. Conclusions: Topiramate increased brain GABA, homocarnosine, and pyrrolidinone to levels that could contribute to its potent antiepileptic action in patients with complex partial seizures.