A 23-year-old woman comes to the emergency department due to chest pain, dyspnea, palpitations, perioral numbness, and sweating. She is extremely anxious and explains that her symptoms came on suddenly for no apparent reason. The patient has had similar episodes 2 or 3 times a week for the past several months. Her blood pressure is 150/90 mm Hg, pulse is 100/min, and respirations are 28/min. Cardiac enzymes are normal, and an ECG shows normal sinus rhythm with no ST-segment or T-wave abnormalities. The patient is diagnosed with panic disorder. She receives medication and feels better within an hour. Which of the following best describes the mechanism of action of the medication she received?

Question

A 23-year-old woman comes to the emergency department due to chest pain, dyspnea, palpitations, perioral numbness, and sweating.  She is extremely anxious and explains that her symptoms came on suddenly for no apparent reason.  The patient has had similar episodes 2 or 3 times a week for the past several months.  Her blood pressure is 150/90 mm Hg, pulse is 100/min, and respirations are 28/min.  Cardiac enzymes are normal, and an ECG shows normal sinus rhythm with no ST-segment or T-wave abnormalities.  The patient is diagnosed with panic disorder.  She receives medication and feels better within an hour.  Which of the following best describes the mechanism of action of the medication she received?

Quizplus · Accepted Answer

11ec160b_3c4f_3dd6_9249_3bd8b02a665c_MD0001_00 This patient exhibits classic symptoms of a panic attack (abrupt and unexpected onset of characteristic physical symptoms and negative medical workup). She most likely received a benzodiazepine, a medication commonly used in emergency settings because it provides rapid relief of acute anxiety. Benzodiazepines work at the GABA_A (γ-aminobutyric acid) receptor complex. GABA is the main inhibitory neurotransmitter in the central nervous system and is synthesized from glutamate using glutamate decarboxylase. The GABA_A receptor complex consists of 5 subunits and a central chloride ion channel, with different binding sites for GABA and various drugs (eg, benzodiazepines, barbiturates). Benzodiazepines act by binding to the benzodiazepine binding site, which allosterically modulates the binding of GABA, resulting in an increased frequency of chloride ion channel opening. The influx of chloride ions into the neurons causes neuronal hyperpolarization and inhibition of the action potential. Barbiturates act at a separate allosteric site and work by prolonging the duration of channel openings in response to GABA and, at higher doses, as GABA_A receptor agonists. (Choice A) GABA_B receptors mediate their actions using G proteins. The skeletal muscle relaxant baclofen is an example of a drug that works as a GABA_B receptor agonist. Benzodiazepines work at the GABA_A receptor. (Choice B) Benzodiazepines do not alter GABA metabolism. Certain anti-epileptic medications, including valproic acid and vigabatrin, function to reduce GABA catabolism. (Choice D) Benzodiazepines do not function through direct activation of the GABA_A receptor. Instead, they work as positive allosteric modulators that promote an increased frequency of channel openings in response to GABA stimulation. (Choice E) Benzodiazepines do not function through blockage of the GABA_A receptor lumen. Examples of drugs that directly block the lumen of ion channels include amiloride (which affects epithelial sodium channels in the distal portions of the nephron) and verapamil (a calcium channel blocker). (Choice F) Prolonged benzodiazepine use has been shown to cause downregulation of GABA_A receptors and may be one of the mechanisms by which benzodiazepine tolerance develops. Educational objective: Benzodiazepines act by binding to the benzodiazepine binding site, which allosterically modulates the binding of GABA, resulting in an increased frequency of chloride ion channel opening. The influx of chloride ions into the neurons causes neuronal hyperpolarization and inhibition of the action potential. __________ References: Benzodiazepine pharmacology and central nervous system-mediated effects. (http://www.ncbi.nlm.nih.gov/pubmed/23789008)

A 23-Year-Old Woman Comes to the Emergency Department Due to Chest