It has a half life of 21 hours and a steady state of the drug is reached in 4 days in patients with normal renal function. Most of the drug (70%) is excreted in the urine unchanged. The remainder is extensively metabolized by hydroxylation, hydrolysis, and glucuronidation. Six metabolites have been identified in humans, none of which constitutes more than 5% of an administered dose. Several cellular targets have been proposed to be relevant to the therapeutic activity of topiramate. These include (1) voltage-gated sodium channels; (2) high-voltage-activated calcium channels; (3) GABA-A receptors; (4) AMPA/kainate receptors; and (5) carbonic anhydrase isoenzymes. There is evidence that topiramate may alter the activity of its targets by modifying their phosphorylation state instead of by a direct action. The effect on sodium channels could be of particular relevance for seizure protection. Although topiramate does inhibit high-voltage-activated calcium channels, the relevance to clinical activity is uncertain. Effects on specific GABA-A receptor isoforms could also contribute to the antiseizure activity of the drug. Topiramate selectively inhibits cytosolic (type II) and membrane associated (type IV) forms of carbonic anhydrase. The action on carbonic anhydrase isoenzymes may contribute to the drugs side-effects, including its propensity to cause metabolic acidosis and calcium phosphate kidney stones. Topiramate inhibits maximal seizure activity in electroconvulsive therapy and in pentylenetetrazol-induced seizures as well as partial and secondarily generalized tonic-clonic seizures in the kindling model, findings predictive of a broad spectrum of activities clinically.
Pemphigus vegetans is a localized form of pemphigus vulgaris. in which there is a localized vegetating papillomatous response. The eroded areas do not heal like usual but form papillomatous growth and vegetation. Accounts for 1-2% of pemphigus cases and is a relatively benign variant of pemphigus vulgaris. Two forms are recognized:

Pemphigus vegetans of Neumann is a localized disease of pemphigus vulgaris slightly more extensive than pemphigus vegetans of Hallopeau. : 568  This type is more common and characterized by early lesions similar to Pemphigus Vulgaris with large bullae and erosive areas. Healing is through formation of granulation tissue. It is named for the Austrian Dermatologist, Isidor Neumann. Pemphigus vegetans of Hallopeau is a disease of localized pemphigus vulgaris. : 568  It is named for François Henri Hallopeau. This type is less aggressive and has pustules not bullae. These pustules heal by verrucous hyperkeratotic vegetations. See also
List of cutaneous conditions
Pemphigus
List of conditions caused by problems with junctional proteins

References


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