WBR0536

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A 10-year-old male is brought to the physician's office by his mother for a recurrent, abrupt transient loss of consciousness and blank stare. Upon appropriate work-up, the patient is diagnosed with absence seizure and is administered a medication to treat his condition. Which of the following mechanisms of action best correlates to the prescribed medication?]]
Answer A	AnswerA::Inactivation of dopamine receptors
Answer A Explanation	AnswerAExp::Antipsychotics are used to treat psychiatric diseases, such as schizophrenia, act by inactivation of dopamine receptors.
Answer B	AnswerB::Inactivation of sodium channels but not effect on GABA
Answer B Explanation	AnswerBExp::Phenytoin's mechanism of action is the inactivation of sodium channels. Although Phenytoin is not commonly administered to treat absence seizures, it is used in tonic-clonic generalized seizure and partial seizures.
Answer C	AnswerC::Concomitant inactivation of sodium channels and activation of GABA
Answer C Explanation	AnswerCExp::Topiramate blocks sodium channels and increases the action of GABA. It is not commonly administered to treat absence seizures, but is effective in treating partial and tonic-clonic generalized seizures.
Answer D	AnswerD::Inactivation of thalamic T-type calcium channels
Answer D Explanation	AnswerDExp::See overall explanation.
Answer E	AnswerE::Inhibition of GABA reuptake
Answer E Explanation	AnswerEExp::Tiagabine, which acts by inhibition of GABA reuptake, is effective in partial seizures, but is not usually used to treat absence seizures.
Right Answer	RightAnswer::D
Explanation	[[Explanation::Ethosuximide, a succinimide antiepileptic drug, is the first line treatment for absence seizure (petit mal). It is a low voltage-activated thalamic T-type calcium channel blocker. Ethosuximide has a rare frequency of adverse drug reactions. Most common side effects include GI distress, fatigue, and headache. A less common, but more severe side effect is Stevens-Johnson syndrome, a dermatologic disorder characterized by fever, bullous formation, and necrosis with skin sloughing. In addition, valproic acid can often be used to treat absence seizures as well. Educational Objective: Ethosuxamide, the first line treatment for absence seizures, is a thalamic T-type calcium channel blocker. References: First Aid 2014 page 485]]
Approved	Approved::Yes
Keyword	WBRKeyword::absence seizure, WBRKeyword::seizures, WBRKeyword::petit mal, WBRKeyword::ethosuximide, WBRKeyword::calcium channel blocker, WBRKeyword::t-type, WBRKeyword::mechanism of action, WBRKeyword::neurological
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