Week 4 notes 13 - D rugs Used to Treat Epilepsy Drugs Used...

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Drugs Used to Treat Epilepsy Drugs Used in the Treatment of Epilepsy - Phenytoin (Dilantin) - Carbamazepine (Tegretol) - Ethosuximide (Zarontin) - Valproate (Depakene) or Divalproex sodium (Depakote) - Lamotrigine (Lamictal) - Phenobarbital (Luminol) Pharmacodynamics of Phenytoin (Dilantin) Like all anticonvulsants, phenytoin raises the seizure threshold of hyperexcitable neurons. It does this by several mechanisms. Most importantly, it blocks sodium channels in the neurons. In addition, phenytoin also blocks potassium and calcium channels and also blocks the release of neurotransmitters (norepinephrine and serotonin). Pharmacokinetics of Phenytoin (Dilantin) Phenytoin can be administered orally and parenterally (I.V. but not I.M.). It is highly protein bound. It is metabolized in the liver and excreted in the urine. Advantages of Phenytoin (Dilantin) - Very effective in partial and generalized tonic-clonic seizures - Available orally (tablets, capsules, suspension) and intravenously; facilitates long term therapy and useful for emergency control of status epilepticus - Oral extended release formulation available for once-a-day dosing - Can be administered concurrently with other anticonvulsants for potentiative drug- drug interaction and better seizure control Disadvantages of Phenytoin (Dilantin) - Cannot be administered I.M. (poor or erratic absorption); a pro-drug called fosphenytoin (Cerebyx) is water-soluble and can be substituted if I.M. administration is needed. - May cause a variety of CNS adverse reactions; dizziness, ataxia, slurred speech, confusion, insomnia - Can produce a rash; drug should be discontinued and if rash is severe, phenytoin is contraindicated thereafter. Patients should be educated to be alert for skin rashes. - Cannot be abruptly discontinued; will provoke status epilepticus - Totally ineffective for absence seizures; requires an additional drug if both types of 1
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Drugs Used to Treat Epilepsy seizures are present in the same patient - Long-term therapy can produce cosmetic problems; acne, hirsutism, coarsening of facial features, gingival hyperplasia - Can produce lymphadenopathy - Can cause hyperglycemia - Teratogenic in pregnancy (Pregnancy category D) Pharmacodynamics of Carbamazepine (Tegretol) Carbamazepine reduces depolarizations and therefore firing of neurons by blocking sodium channels in neurons. The highly excitable neurons are most affected. The threshold for depolarizations, and therefore the seizure threshold, is increased.
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