WBR0092
| Author | [[PageAuthor::Gonzalo Romero (reviewed by Yazan Daaboul, Jad Al Danaf, Rim Halaby, M.D. [1])]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pharmacology |
| Sub Category | SubCategory::Genitourinary |
| Prompt | [[Prompt::A 35-year-old man presents to the emergency department for a persistent and painful erection for the past 5 hours. Upon further questioning, he reports he is a single man with no recent sexual activity or trauma to the genitals. The patient also denies any personal or family history of coagulopathy or hemoglobinopathy. His past medical history is only significant for insomnia and major depression for the past 4 months, for which he was prescribed an antidepressant medication whose name he cannot recall. In the ED, the patient's blood pressure is 176/110 mmHg, temperature is 37 °C (98.6 °F), heart rate is 98/minute, and respiratory rate is 20/minute. On physical examination, the patient appears in pain. His penis is fully erect and tender, with no color changes or other signs of necrosis. The physician in the ED suspects the patient's symptoms may be drug-induced. Which of the following is the mechanism of action of the drug responsible for the patient's symptoms?]] |
| Answer A | AnswerA::Serotonin reuptake inhibitor |
| Answer A Explanation | [[AnswerAExp::The sleep medication prescribed for the patient is most likely trazodone. It is an atypical antidepressant that belongs to the serotonin antagonist and reuptake inhibitor (SARI) class of antidepressants. It is usually prescribed to treat insomnia in patients with major depressive symptoms, and has also been shown to have anxiolytic properties. Trazodone is thought to cause priapism through its antagonistic effect on alpha adrenergic receptors.]] |
| Answer B | AnswerB::Norepinephrine reuptake inhibitor |
| Answer B Explanation | [[AnswerBExp::Maprotiline is an atypical antidepressant which blocks norepinephrine reuptake. It can cause sedation as a side effect.]] |
| Answer C | AnswerC::Serotonin receptor agonist |
| Answer C Explanation | [[AnswerCExp::Buspirone, which is used to treat general anxiety disorder, stimulates serotonin (5-HT1a) receptors. It does not cause sedation, addiction or tolerance.]] |
| Answer D | AnswerD::Alpha-2 receptor antagonist |
| Answer D Explanation | [[AnswerDExp::Mirtazapine is an atypical antidepressant. It blocks alpha-2 receptors in the presynaptic neurons which increases the release of norepinephrine and serotonin. It causes sedation and therefore can be used in depressed patients with insomnia. It might also cause an increase in appetite with possible weight gain.]] |
| Answer E | AnswerE::GABA positive allosteric modulators |
| Answer E Explanation | [[AnswerEExp::Different drugs act by increasing the opening of GABA channels such as benzodiazepines and barbiturates.]] |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::Trazadone is an atypical antidepressant that belongs to the serotonin antagonist and reuptake inhibitor (SARI) class of antidepressants. It is a "multifunctional" drug because of its varying binding properties at low doses vs. high doses. At low doses, trazodone acts as a 5-HT2A antagonist, and has effects of H1 receptors and alpha-1 adrenergic receptors. At higher doses, trazadone blocks the serotonin transporter (SERT). It is mainly administered to treat depression associated with insomnia due to its antidepressant and sedating effects. Accordingly, trazodone is called a "serotonin antagonist-reuptake inhibitor" (SARI) whose action on both histamine and serotonin is required for appropriate therapeutic effects.
An important but rare side effect of trazadone is low-flow priapism, which is a painful sustained penile erection for more than 4 hours. Trazadone also causes sedation, nausea, and postural hypotension. While most cases of priapism are idiopathic, other common causes of priapism include genital trauma, and hemoglobinopathies such as sickle cell disease. Drug-induced priapism accounts for approximately 30% of all cases. Priapism is a clinical diagnosis; differentiation between low-flow and high-flow priapism is important for appropriate management. While most cases are considered low-flow painful ischemic priapisms, high-flow painless priapism due to trauma and fistula formation must be ruled out. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::trazodone, WBRKeyword::priapism, WBRKeyword::depression, WBRKeyword::insomnia, WBRKeyword::serotonin reuptake inhibitor |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
Image [[WBRImage::|]] Caption WBRImageCaption::no-display Position [[WBRImagePlace::Explanation|]]