Topiramate (brand name Topamax) is an anticonvulsant drug produced by Ortho-McNeil Neurologics, a division of Johnson & Johnson. It is used to treat epilepsy in both children and adults. In children it is also indicated for treatment of Lennox-Gastaut syndrome (a disorder that causes seizures and developmental delays). It is also Food and Drug Administration (FDA) approved for, and now most frequently prescribed for, the prevention of migraines. [Wikipedia]. A combination product containing phentermine and topiramate extended-release called QSYMIA® is indicated for the management of obesity. On August 2013, an extended released formulation, marketed as Trokendi XR has been approved for the management of partial onset, tonic-clonic, and Lennox-Gastaut Syndrome seizures.
Used for the treatment and control of partial seizures and severe tonic-clonic (grand mal) seizures and also for the prevention of migraine headaches. In children it is also used for treatment of Lennox-Gastaut syndrome. Qsymia® is indicated for the treatment and management of obesity.
Topiramate is an anticonvulsant indicated in the treatment of epilepsy and migraine. Topiramate enhances GABA-activated chloride channels. In addition, topiramate inhibits excitatory neurotransmission, through actions on kainate and AMPA receptors. There is evidence that topiramate has a specific effect on GluR5 kainate receptors. It is also an inhibitor of carbonic anhydrase, particular subtypes II and IV, but this action is weak and unlikely to be related to its anticonvulsant actions, but may account for the bad taste and the development of renal stones seen during treatment. Its possible effect as a mood stabilizer seems to occur before anticonvulsant qualities at lower dosages. Topiramate inhibits maximal electroshock and pentylenetetrazol-induced seizures as well as partial and secundarily generalized tonic-clonic seizures in the kindling model, findings predective of a broad spectrum of antiseizure activities clinically.
Mechanism of action
The precise mechanism of action of topiramate is not known. However, studies have shown that topiramate blocks the action potentials elicited repetitively by a sustained depolarization of the neurons in a time-dependent manner, suggesting a state-dependent sodium channel blocking action. Topiramate also augments the activity of the neurotransmitter gamma-aminobutyrate (GABA) at some subtypes of the GABA<sub>A</sub> receptor (controls an integral chloride channel), indicating a possible mechanism through potentiation of the activity of GABA. Topiramate also demonstrates antagonism of the AMPA/kainate subtype of the glutamate excitatory amino acid receptor. It also inhibits carbonic anhydrase (particularly isozymes II and IV), but this action is weak and unlikely to be related to its anticonvulsant actions.
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