WBR0536
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pharmacology |
| Sub Category | SubCategory::Neurology |
| Prompt | [[Prompt::A 10 year old boy is brought by his mother to the physician's office for recurrent abrupt transient loss of consciousness and a blank stare. Following appropriate work-up, the patient is diagnosed with absence seizure. The patient is started on a new medication to treat his condition. Which of the following best describes the mechanism of action of 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 is not commonly used for absence seizures. It is used, however, in tonic-clonic generalized seizure and partial seizures. Its mechanism of action is inactivation of sodium channels.
Also, carbamazepine is not first line treatment for absence seizures. It is a first line treatment for partial seizures and tonic-clonic generalized seizures. Similar to phenytoin, carbamazepine acts by inactivation of sodium channels.]] |
| 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 used in absence seizures. It is effective in partial and tonic-clonic generalized seizures. |
| Answer D | AnswerD::Inactivation of thalamic T-type calcium channels |
| Answer D Explanation | AnswerDExp::Ethosuximide is considered first line treatment for absence seizures. It blocks thalamic T-type calcium channels. |
| Answer E | AnswerE::Inhibition of GABA reuptake |
| Answer E Explanation | AnswerEExp::Tiagabine is effective in partial seizures. It acts by inhibition of GABA reuptake. It is not usually used to treat absence seizures. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Ethosuximide is a succinimide antiepileptic drug that is considered the first line treatment for absence seizure (petit mal). It is a low voltage-activated thalamic T-type calcium channel blocker.
Ethosuximide has a relatively safe side effect profile with 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 to ethosuximide, valproic acid can often be used to treat absence seizures as well. Educational Objective: Ethosuxamide is the first line treatment for absence seizures. It is a thalamic T-type calcium channel blocker. |
| Approved | Approved::No |
| Keyword | WBRKeyword::absence, WBRKeyword::seizure, WBRKeyword::seizures, WBRKeyword::petit, WBRKeyword::mal, WBRKeyword::petit mal, WBRKeyword::ethosuximide, WBRKeyword::calcium, WBRKeyword::channel, WBRKeyword::blocker, WBRKeyword::t-type, WBRKeyword::t type, WBRKeyword::thalamic, WBRKeyword::mechanism, WBRKeyword::action |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |