Pharmacology

Carbamazepine's mechanism of action in the treatment of seizures and pain syndromes is controversial, but probably results from blockade of voltage-sensitive sodium channels or enhancement of GABA activity. Its effect in the treatment of these disorders is almost immediate. Its mechanism of action in the treatment of psychiatric disorders is less clear, but is thought to occur by another mechanism, given that the treatment response time may be longer. Carbamazepine is known to affect numerous neurotransmitter systems, and one or more of these effects is thought to account for its success in treating psychiatric disorders. (1. ,16)

H4>Pharmacokinetics

Carbamazepine is absorbed slowly, with peak plasma levels occurring 4 to 5 h after administration of the tablets. Absorption is faster for the carbamazepine suspension, and slower for carbamazepine extended-release tablets. Oral bioavailability is about 80 per cent. Plasma protein binding is approximately 75 per cent. The half-life of carbamazepine is variable, as it induces its own metabolism with chronic administration (autoinduction). Initially, the half-life ranges from 18 to 65 h, but after autoinduction is complete (usually 3 to 5 weeks) it is decreased to 5 to 25 h. Children metabolize carbamazepine more rapidly than adults, and therefore require higher doses to achieve similar levels. Carbamazepine is metabolized in the liver by the cytochrome P-450 system to a wide variety of metabolites, some which have antiepileptic activity. The predominant metabolite is carbamazepine-10,11-epoxide, which is further metabolized by epoxide hydrolase to an inactive form. Valproate inhibits epoxide hydrolase, and thus when valproate and carbamazepine are combined, the concentration of carbamazepine-10,11-epoxide increases. Most of carbamazepine's metabolites are excreted as glucuronide conjugates in the urine. (1. 1 17 and !8)

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Break Free From Passive Aggression

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