WBR1004

Author	[[PageAuthor::Vidit Bhargava, M.B.B.S [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A 5 yr old child is brought to the pediatrician by concerned parents. He is reported to have occasional episodes of “staring into space” which last about 1-2 mins, the child is unarousable during the period even by painful stimuli and is not in his normal senses for some time afterwards. There are no jerky movements or tonic muscle spasms as reported by the parents. On doing EEG a 3-4 Hz spike and slow wave complex is noticed. What is the mechanism of action of drug most commonly used to treat this condition?]]
Answer A	AnswerA::Blocks T-type Ca2+ channel.
Answer A Explanation	[[AnswerAExp::Several studies conducted over a period of years have hinted that the most common mechanism of action of ethosuximide is blocking of T-type Ca2+ channel, thus decreasing membrane excitability.]]
Answer B	AnswerB::Decreases influx of Na+ across cell membrane channels.
Answer B Explanation	[[AnswerBExp::It is the most common mechanism of action by which a number of anti epileptic drugs act such as carbamazepine, phenytoin, fosphenytoin etc.]]
Answer C	[[AnswerC::Increasing GABA in brain by inhibiting GABA transaminase.]]
Answer C Explanation	[[AnswerCExp::Drugs acting by this mechanism include vigabatrin, however it is not the most common drug used to treat absence seizure.]]
Answer D	[[AnswerD::Decreases influx of Na+ across cell membrane channels, also increases GABA in brain and blocks T-type Ca2+ channel.]]
Answer D Explanation	AnswerDExp::Sodium valproate acts my a multitude of actions, thought the predominant amongst them is decreasing influx of Na+ across cell membrane channels.
Answer E	AnswerE::Antagonism of AMPA/kainate subtype of the glutamate receptor
Answer E Explanation	[[AnswerEExp::One of the several mechanisms by which topiramate acts.]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::The presentation given here is characteristic for an absence seizure with: Staring into space Lasting 1-2 mins Post seizure confusion Electro-encephalogram depicting 3-4 Hz spike and slow wave complex The first choice drug for absence seizures is ethosuximide, which acts on neuronal membrane to block T-type Ca2+ channel thus decreasing membrane excitability. The second line drug for absence seizures is sodium valproate Educational Objective: The most common mechanism of action of ethosuximide is blocking of T-type Ca2+ channel, thus decreasing membrane excitability. References: Page 451 FA STEP 1 2013]]
Approved	Approved::No
Keyword	WBRKeyword::ethosuximide absence seizure
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Order in Linked Questions	LinkedOrder::