Epilepsy mechanisms

Emilien G, Maloteaux JM. Pharmacological management of epilepsy. Mechanism of action, pharmacokinetic drug interactions, and new drug discovery possibilities. Int J Clin Pharmacol Ther 1998 36 181-194. 

How the drugs currently available for the treatment of epilepsy may utilise these mechanisms will now be considered. 

There is no shortage of AEDs (Fig. 16.7) but it is not appropriate to consider them in detail in this text other than to see how their mechanisms of action comply with and illustrate those proposed above (Fig. 16.6) for the control of epileptic seizures (see Meldrum 1996 Upton 1994). The decision on which drug to use depends not only on their proven efficacy in a particular type of epilepsy (some drugs are inactive in certain forms) but also what side-effects they have—many are sedative — how they interact with other drugs and how often they need to be taken. Compliance is a problem over a long period if dosing is required more than once a day. It is probably acceptable in reality, if not scientifically, to divide the drugs into old-established AEDs and new AEDs. Only the latter have been developed chemically to modify the known synaptic function of the amino acids. 

Phenobarbitone was the first AED and was introduced in 1912. It was largely replaced in 1932 by phenytoin for the management of tonic-xilonic seizures and partial and secondary epilepsy. Carbamazepine followed, then ethosuximide for absence seizures and valproic acid. These remained, apart from the introduction of the benzodiazepines, the mainstay of therapy until the last decade. They were introduced solely on their ability to control experimentally induced seizures. Their mechanisms of action were unknown and no thought was given to the possibility of NT modification and in fact subsequent research has shown that with the exception of the benzodiazepines none of them work primarily through NT manipulation. They act directly on neuronal excitability. 

That the hippocampus is important for memory is generally accepted. This is not because it is a site of major degeneration in AzD, that finding can only be used to account for the memory loss if memory is known to be dependent on the hippocampus, but because lesions of that region are known to impair memory. Case reports in the medical literature are rightly mistrusted but few people have felt inclined to disregard the evidence presented by one 27-year-old male mechanic who underwent bilateral hippocampal removal for intractable epilepsy in Montreal in 1953. While that condition was improved the operation has not been repeated because memory loss was almost total, so while he appeared to behave reasonably normally (and still does), he cannot remember where he lives, what he has just eaten or the person he met a few minutes previously. 

GABA) mechanisms, and blockade of glutamatergic mechanisms. Because epilepsy is a disease with multiple etiologies, these combinations of mechanisms explain the clinical efficacy of this drug in this disease [78]. 

Cellular mechanisms underlying hyperexcitability have been analyzed by electrophysiological studies of hippocampal slices isolated from animals with epilepsy 632... 

Identifying molecular mechanisms of epileptogenesis will provide new targets for developing small molecules to prevent epilepsy 633... 

The epilepsies constitute a common, serious neurological disorder in humans, affecting approximately 60 million people worldwide. Well in excess of 40 distinct epileptic syndromes have been identified to date. Current treatment is only symptomatic except in uncommon instances when surgical treatment is possible. While available antiseizure medications target ion channels such as the y-amino-butyric acid (GABA)a receptor and voltage activated sodium (Na+) channels, current research seeks to elucidate the cellular and molecular mechanisms by which a normal brain becomes epileptic. Hopefully, this research will lead to the identification of new targets for which small molecules can be identified and used for prevention or cure of epilepsy. 

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