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. |
| 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 |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |