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Chapter 19 Antiseizure Drugs Epilepsy- group of disorders characterized by excessive excitability of neurons in the CNS.What causes a seizure? 75% of all seizures are idiopathic. The other 25% not related to epilepsy could result from fever, hypoglycemic reaction, electrolyte imbalance, metabolic imbalance, and alcohol or drug use.Agents that treat seizures-antiepileptic drugs (AEDs) and antiseizuresTwo categories of seizures: generalized and partial. a person may also have mixed seizures. there are several specific seizures that fall under these categories (table 19.1)Partial (simple)-occurs in motor, sensory, autonomic and psychic forms; no loss of consciousnessPartial (complex)-involves one hemisphere of the brain; no loss of consciousness occurs in simple partial seizures but there is a loss of consciousness in complex partial seizuresGeneralized seizure-seizures involve both cerebral hemisphere of the brainTonic (gran mal) sustained muscle contractionClonic-dysrhythmic muscle contractionTonic clonic seizure-also called grand mal seizure, the most common form. in the tonic phase skeletal muscles contract in spasm for 3-5 sec. in the clonic phase a dysrhythmicmuscular contraction occurs with a jerkiness of legs and arms 2-4 minPetit Mal (absent)- all called petit mal seizure. brief loss of consciousness (10 sec), with fewer than 3 spike waves on EEG. usually in children.International Classification of seizures: Table 19.1 pg 247
Generalized type of drugs used to treat seizures:hydantoins (phenytoin)long-acting barbiturates (phenobarbital, mephobarbital)SuccinimidesBenzodiazepinesCarbamazepineValproate-antiseizure drugs are not indicated for all types of seizures, some are better at treating certain types3 Different ways Antiseizure Medication Works (Mechanism of Action):1. Suppressing sodium influxthrough the drug binding to the sodium channel when it is inactivated which prolongs the channel inactivation and thereby prevents neuron firing. drugs that do this are phenytoin, fosphenytoin, carbamazepine, valproic acid, topiramate, and zonisamide2. Suppressing the calcium influx,which prevents the electric current generated by the calcium ions to the T-type calcium channel. valproic acid and ethosuximide work this way3. Increasing the action of gamma-aminobutyric acid (GABA) which inhibits neurotransmitters through the brain. barbiturates, benzodiazepines and tiagabine are drugs that work this waymyoclonic seizure-isolated clonic contraction of jerks that last 3-10 sec. may be limited
to one limb or entire body. can be secondary to neurologic disorder like Tay-Sachs diseaseatonic seizure-head drop, loss of posture and sudden loss of muscle tone occurs.