A group of researchers is studying various inhaled substances to determine their anesthetic properties. In particular, they are trying to identify an anesthetic with fast onset and quick recovery for use in emergencies. They determine the following data:
Inhalational anesthetic Blood-gas partition coefficient
A 0.15
B 0.92
C 5.42
Which of the following statements is accurate with regard to these inhaled anesthetic substances?
Q502
A 55-year-old man presents with intense pain in his left knee that started after returning from a camping trip 2 days ago, during which he consumed copious amounts of alcohol and red meat. He says he has had similar episodes in the past that resolved spontaneously usually over a period of about 10 days. His past medical history is significant for essential hypertension managed with hydrochlorothiazide 20 mg/day. The patient is afebrile, and his vital signs are within normal limits. Physical examination shows edema, warmth, and erythema of the left knee, which is also severely tender to palpation. The range of motion at the left knee joint is limited. A joint arthrocentesis of the left knee is performed, and synovial fluid analysis reveals 20,000 neutrophils and the following image is seen under polarized light microscopy (see image). Which of the following is the best course of treatment for this patient's condition?
Q503
A 25-year-old man comes to the physician because of an 8-hour history of painful leg cramping, runny nose, chills, diarrhea, and abdominal pain. Examination shows cool, damp skin with piloerection. The pupils are 7 mm in diameter and equal in size. Deep tendon reflexes are 3+ bilaterally. The diagnosis of opioid withdrawal is made. After the patient is stabilized, the physician initiates a withdrawal regimen with methadone. Which of the following characteristics makes this drug a suitable substance for the treatment of this patient's addiction?
Q504
An 82-year-old male with a history of congestive heart failure presented with new-onset atrial fibrillation. He was initially started on carvedilol, but he now requires an additional agent for rate control. He is started on a medicine and is warned by his physician of the following potential side effects associated with this therapy: nausea, vomiting, confusion, blurry yellow vision, electrolyte abnormalities, and potentially fatal arrhythmia. Which of the following is most likely to increase this patient's susceptibility to the toxic effects associated with this medication?
Q505
A 22-year-old woman presents to the emergency department feeling lightheaded and states that her heart is racing. She does not have a history of any chronic medical conditions. She is a college sophomore and plays club volleyball. Although she feels stressed about her upcoming final exams next week, she limits her caffeine intake to 3 cups of coffee per day to get a good night sleep. She notes that her brother takes medication for some type of heart condition, but she does not know the name of it. Both her parents are alive and well. She denies recent illness, injuries, or use of cigarettes, alcohol, or recreational drugs. The pertinent negatives from the review of systems include an absence of fever, nausea, vomiting, sweating, fatigue, or change in bowel habits. The vital signs include: temperature 36.8°C (98.2°F), heart rate 125/min, respiratory rate 15/min, blood pressure 90/75 mm Hg, and oxygen saturation of 100% on room air. The laboratory results are within normal limits. The ECG is significant for a shortened PR interval and widened QRS. Which of the following medications should the patient avoid in this scenario?
Q506
A 71-year-old man with recently diagnosed small-cell lung cancer sees his physician because of increasing weakness over the past 3 months. He is unable to climb stairs or comb his hair. His weakness is worse after inactivity and improves with exercise. He is a former smoker with a 30-pack-year history. He is currently preparing for initiation of chemotherapy. His vital signs are within normal limits. On examination, ptosis of both eyelids is seen. Dry oral mucosa is notable. Significant weakness is detected in all four proximal extremities. The patellar and biceps reflexes are absent. Auscultation of the lungs reveals generalized wheezing and rhonchi. Which of the following is the most likely underlying mechanism for this patient’s weakness?
Q507
A 50-year-old woman comes to the physician for the evaluation of excessive hair growth on her chin over the past 2 weeks. She also reports progressive enlargement of her gums. Three months ago, she underwent a liver transplantation due to Wilson disease. Following the procedure, the patient was started on transplant rejection prophylaxis. She has a history of poorly-controlled type 2 diabetes mellitus. Temperature is 37°C (98.6°F), pulse is 80/min, respirations are 22/min, and blood pressure is 150/80 mm Hg. Physical examination shows dark-pigmented, coarse hair on the chin, upper lip, and chest. The gingiva and the labial mucosa are swollen. There is a well-healed scar on her right lower abdomen. Which of the following drugs is the most likely cause of this patient's findings?
Q508
A 54-year-old man comes to the emergency department because of episodic palpitations for the past 12 hours. He has no chest pain. He has coronary artery disease and type 2 diabetes mellitus. His current medications include aspirin, insulin, and atorvastatin. His pulse is 155/min and blood pressure is 116/77 mm Hg. Physical examination shows no abnormalities. An ECG shows monomorphic ventricular tachycardia. An amiodarone bolus and infusion is given, and the ventricular tachycardia converts to normal sinus rhythm. He is discharged home with oral amiodarone. Which of the following is the most likely adverse effect associated with long-term use of this medication?
Q509
A 34-year-old female presents to the emergency room with headache and palpitations. She is sweating profusely and appears tremulous on exam. Vital signs are as follows: HR 120, BP 190/110, RR 18, O2 99% on room air, and Temp 37C. Urinary metanephrines and catechols are positive. Which of the following medical regimens is contraindicated as a first-line therapy in this patient?
Q510
A 3-year-old toddler was rushed to the emergency department after consuming peanut butter crackers at daycare. The daycare staff report that the patient has a severe allergy to peanut butter and he was offered the crackers by mistake. The patient is in acute distress. The vital signs include: blood pressure 60/40 mm Hg and heart rate 110/min. There is audible inspiratory stridor and the respiratory rate is 27/min. Upon examination, his chest is covered in a maculopapular rash. Intubation is attempted and failed due to extensive laryngeal edema. The decision for cricothyrotomy is made. Which of the following is the most likely mechanism of this pathology?
Autonomic/CV Drugs US Medical PG Practice Questions and MCQs
Question 501: A group of researchers is studying various inhaled substances to determine their anesthetic properties. In particular, they are trying to identify an anesthetic with fast onset and quick recovery for use in emergencies. They determine the following data:
Inhalational anesthetic Blood-gas partition coefficient
A 0.15
B 0.92
C 5.42
Which of the following statements is accurate with regard to these inhaled anesthetic substances?
A. Agent C has the fastest onset of action
B. Agent A has the fastest onset of action (Correct Answer)
C. Agent B is the most potent
D. Agent B has the fastest onset of action
E. Agent A is the most potent
Explanation: ***Agent A has the fastest onset of action***
- **Agent A** has the lowest blood-gas partition coefficient (0.15), indicating very low solubility in blood.
- A **low blood-gas partition coefficient** means the anesthetic quickly equilibrates between the lungs and blood, leading to a rapid rise in partial pressure in the brain and thus **fast onset of action** and **quick recovery**.
*Agent C has the fastest onset of action*
- **Agent C** has the highest blood-gas partition coefficient (5.42), indicating high solubility in blood.
- High solubility means the anesthetic takes longer to saturate the blood and reach the brain, resulting in a **slow onset of action** and **slow recovery**.
*Agent B is the most potent*
- **Potency** of an inhaled anesthetic is inversely related to its **Minimum Alveolar Concentration (MAC)**, not directly to its blood-gas partition coefficient.
- While a higher blood-gas coefficient can sometimes correlate with other properties, it does not directly determine potency.
*Agent B has the fastest onset of action*
- **Agent B** has a blood-gas partition coefficient of 0.92, which is higher than Agent A (0.15).
- A higher blood-gas partition coefficient means the anesthetic is more soluble in blood, leading to a **slower onset of action** compared to Agent A.
*Agent A is the most potent*
- **Agent A** has the lowest blood-gas partition coefficient (0.15), which indicates **fast onset** and **rapid recovery**, but not necessarily high potency.
- **Potency** is determined by MAC (Minimum Alveolar Concentration), which is the concentration of anesthetic at 1 atmosphere that produces immobility in 50% of patients challenged with a surgical incision.
Question 502: A 55-year-old man presents with intense pain in his left knee that started after returning from a camping trip 2 days ago, during which he consumed copious amounts of alcohol and red meat. He says he has had similar episodes in the past that resolved spontaneously usually over a period of about 10 days. His past medical history is significant for essential hypertension managed with hydrochlorothiazide 20 mg/day. The patient is afebrile, and his vital signs are within normal limits. Physical examination shows edema, warmth, and erythema of the left knee, which is also severely tender to palpation. The range of motion at the left knee joint is limited. A joint arthrocentesis of the left knee is performed, and synovial fluid analysis reveals 20,000 neutrophils and the following image is seen under polarized light microscopy (see image). Which of the following is the best course of treatment for this patient's condition?
A. Colchicine
B. Uricosuric drug
C. Intra-articular steroid injection
D. Xanthine oxidase inhibitor
E. Nonsteroidal antiinflammatory drugs (Correct Answer)
Explanation: ***Nonsteroidal antiinflammatory drugs***
- **NSAIDs** are the first-line treatment for acute gout attacks due to their potent anti-inflammatory effects. They rapidly reduce pain and swelling by inhibiting prostaglandin synthesis.
- This patient presents with classic symptoms of an acute gout flare, including sudden onset of **severe monoarticular pain**, **swelling**, **warmth**, and **erythema** of the knee following dietary indiscretion and **hydrochlorothiazide** use, which can precipitate gout. The synovial fluid analysis showing **20,000 neutrophils** and the characteristic crystal image (negative birefringence) confirms the diagnosis of gout.
*Colchicine*
- **Colchicine** is an effective anti-inflammatory agent for acute gout, particularly if initiated within 36 hours of symptom onset. However, it is generally considered a second-line option to NSAIDs for initial management due to potential gastrointestinal side effects.
- While suitable, the question asks for the **best course of treatment**, and NSAIDs often provide faster and more robust symptom relief with fewer immediate side effects for most patients in acute settings.
*Uricosuric drug*
- **Uricosuric drugs** like probenecid increase the excretion of uric acid in the urine and are used for **long-term management of hyperuricemia** in patients who underexcrete uric acid. They are not indicated for the treatment of an acute gout attack.
- Initiating a uricosuric drug during an acute attack can potentially worsen symptoms by mobilizing uric acid crystals.
*Intra-articular steroid injection*
- **Intra-articular steroid injections** are effective for acute gout, especially when a single joint is affected, or when NSAIDs and colchicine are contraindicated or poorly tolerated.
- While it can provide rapid relief, **NSAIDs** are generally preferred as the initial systemic treatment for acute gout in patients without contraindications due to ease of administration and broad efficacy.
*Xanthine oxidase inhibitor*
- **Xanthine oxidase inhibitors (XOIs)** like allopurinol or febuxostat reduce uric acid production and are used for **long-term management of hyperuricemia** to prevent future gout attacks. They are not used to treat acute gout.
- Initiating an XOI during an acute attack can potentially worsen or prolong the flare by altering serum uric acid levels. These medications should typically be started after the acute flare has resolved and often with concurrent anti-inflammatory prophylaxis.
Question 503: A 25-year-old man comes to the physician because of an 8-hour history of painful leg cramping, runny nose, chills, diarrhea, and abdominal pain. Examination shows cool, damp skin with piloerection. The pupils are 7 mm in diameter and equal in size. Deep tendon reflexes are 3+ bilaterally. The diagnosis of opioid withdrawal is made. After the patient is stabilized, the physician initiates a withdrawal regimen with methadone. Which of the following characteristics makes this drug a suitable substance for the treatment of this patient's addiction?
A. Rapid onset of action
B. Low tolerance potential
C. Long elimination half-life (Correct Answer)
D. Low dependence risk
E. Limited potency
Explanation: ***Long elimination half-life***
- **Methadone's long half-life** allows for steady drug levels, preventing the rapid fluctuations that trigger severe withdrawal symptoms.
- This characteristic enables **once-daily dosing**, simplifying treatment and reducing the likelihood of illicit drug-seeking behavior.
*Rapid onset of action*
- While methadone does have a relatively quick onset, it's not its primary advantage in **opioid addiction treatment**.
- **Buprenorphine** often has a faster onset and is used in a different capacity for induction of treatment.
*Low tolerance potential*
- **Methadone** is an opioid agonist and, like other opioids, patients can develop **tolerance** to its effects over time.
- Its utility in addiction treatment comes from its ability to stabilize opioid receptors, not from a lack of tolerance development.
*Low dependence risk*
- **Methadone** is an opioid and carries a significant risk of **physical dependence**.
- The goal of methadone maintenance is to manage this dependence in a controlled medical setting, reducing harm associated with illicit opioid use.
*Limited potency*
- **Methadone** is a potent opioid, similar in potency to morphine, which contributes to its effectiveness in managing severe withdrawal symptoms and cravings.
- Its high potency is a key factor in its therapeutic benefit, not a limitation.
Question 504: An 82-year-old male with a history of congestive heart failure presented with new-onset atrial fibrillation. He was initially started on carvedilol, but he now requires an additional agent for rate control. He is started on a medicine and is warned by his physician of the following potential side effects associated with this therapy: nausea, vomiting, confusion, blurry yellow vision, electrolyte abnormalities, and potentially fatal arrhythmia. Which of the following is most likely to increase this patient's susceptibility to the toxic effects associated with this medication?
A. Hyperkalemia
B. Elevated AST and ALT
C. Increased GFR with normal creatinine
D. Hypokalemia (Correct Answer)
E. Hyponatremia
Explanation: ***Hypokalemia***
- The symptoms described (nausea, vomiting, confusion, blurry yellow vision, potentially fatal arrhythmias) are classic for **digoxin toxicity**.
- **Hypokalemia** increases the binding of digoxin to the **Na+/K+-ATPase pump**, exacerbating its effects and increasing the risk of toxicity.
*Hyperkalemia*
- **Hyperkalemia** actually **inhibits** digoxin binding to the Na+/K+-ATPase pump.
- This can reduce the therapeutic efficacy and the toxic effects of digoxin.
*Elevated AST and ALT*
- Elevated AST and ALT indicate **liver dysfunction**, which can affect the metabolism of certain drugs.
- However, digoxin is primarily eliminated by the **kidneys**, so liver enzyme abnormalities are not a primary risk factor for digoxin toxicity.
*Increased GFR with normal creatinine*
- An increased **Glomerular Filtration Rate (GFR)** would lead to more rapid renal clearance of digoxin.
- This would **decrease** the risk of digoxin accumulation and toxicity, rather than increase it.
*Hyponatremia*
- While electrolyte imbalances can be associated with cardiac conditions, **hyponatremia** itself does not directly increase the susceptibility to digoxin toxicity.
- The most critical electrolyte imbalance for digoxin toxicity is **hypokalemia**.
Question 505: A 22-year-old woman presents to the emergency department feeling lightheaded and states that her heart is racing. She does not have a history of any chronic medical conditions. She is a college sophomore and plays club volleyball. Although she feels stressed about her upcoming final exams next week, she limits her caffeine intake to 3 cups of coffee per day to get a good night sleep. She notes that her brother takes medication for some type of heart condition, but she does not know the name of it. Both her parents are alive and well. She denies recent illness, injuries, or use of cigarettes, alcohol, or recreational drugs. The pertinent negatives from the review of systems include an absence of fever, nausea, vomiting, sweating, fatigue, or change in bowel habits. The vital signs include: temperature 36.8°C (98.2°F), heart rate 125/min, respiratory rate 15/min, blood pressure 90/75 mm Hg, and oxygen saturation of 100% on room air. The laboratory results are within normal limits. The ECG is significant for a shortened PR interval and widened QRS. Which of the following medications should the patient avoid in this scenario?
A. Amlodipine
B. Procainamide
C. Diltiazem
D. Verapamil (Correct Answer)
E. Metoprolol
Explanation: ***Verapamil***
- The ECG findings of a **shortened PR interval** and **widened QRS** are characteristic of **Wolff-Parkinson-White (WPW) syndrome**, an accessory pathway that can bypass the AV node.
- Verapamil is a **non-dihydropyridine calcium channel blocker** that blocks the AV node and can paradoxically increase conduction down the accessory pathway in WPW, potentially leading to **ventricular fibrillation** if an atrial tachyarrhythmia is present.
- **Verapamil is the most classically contraindicated medication in WPW syndrome** and is the prototype drug to avoid in this condition.
*Amlodipine*
- Amlodipine is a **dihydropyridine calcium channel blocker** primarily used for hypertension and angina.
- It has minimal effect on the AV node and does not carry the same risk as non-dihydropyridine calcium channel blockers in WPW syndrome.
*Procainamide*
- **Procainamide is a Class Ia antiarrhythmic** that can be used to treat tachyarrhythmias related to WPW syndrome, as it prolongs the refractory period of the accessory pathway.
- It would be a potential **treatment option**, not a medication to avoid, especially for antidromic atrioventricular reentrant tachycardia (AVRT) in WPW.
*Diltiazem*
- Similar to verapamil, diltiazem is a **non-dihydropyridine calcium channel blocker** that blocks the AV node.
- While it carries similar risks to verapamil in WPW syndrome, **verapamil is more classically emphasized** as the prototypical contraindicated medication in medical education and board examinations.
*Metoprolol*
- Metoprolol is a **beta-blocker** that slows conduction through the AV node.
- While beta-blockers are also generally **avoided in WPW syndrome with atrial fibrillation**, **AV nodal blocking calcium channel blockers (especially verapamil) are considered the primary contraindication** due to more pronounced effects on accessory pathway conduction.
Question 506: A 71-year-old man with recently diagnosed small-cell lung cancer sees his physician because of increasing weakness over the past 3 months. He is unable to climb stairs or comb his hair. His weakness is worse after inactivity and improves with exercise. He is a former smoker with a 30-pack-year history. He is currently preparing for initiation of chemotherapy. His vital signs are within normal limits. On examination, ptosis of both eyelids is seen. Dry oral mucosa is notable. Significant weakness is detected in all four proximal extremities. The patellar and biceps reflexes are absent. Auscultation of the lungs reveals generalized wheezing and rhonchi. Which of the following is the most likely underlying mechanism for this patient’s weakness?
A. Acute autoimmune demyelination of axons
B. Endomysial CD8+ T cell infiltration with vacuoles and inclusion bodies
C. Necrotizing vasculitis with granuloma formation
D. Reduced number of available postsynaptic acetylcholine receptors
E. Autoantibody-impaired acetylcholine release from nerve terminals (Correct Answer)
Explanation: ***Autoantibody-impaired acetylcholine release from nerve terminals***
- This patient's progressive, proximal muscle weakness, **ptosis**, and **absent deep tendon reflexes**, particularly with improvement upon exercise, are classic signs of **Lambert-Eaton myasthenic syndrome (LEMS)**.
- LEMS is a **paraneoplastic syndrome** strongly associated with **small-cell lung cancer (SCLC)**, caused by autoantibodies targeting presynaptic **voltage-gated calcium channels**, thus impairing acetylcholine release.
*Acute autoimmune demyelination of axons*
- This description is characteristic of **Guillain-Barré syndrome (GBS)**, which typically presents with **ascending paralysis** and is often preceded by an infection.
- Unlike LEMS, GBS usually causes worsening weakness with activity and is not directly associated with cancer in this paraneoplastic manner.
*Endomysial CD8+ T cell infiltration with vacuoles and inclusion bodies*
- This pathological finding is characteristic of **inclusion body myositis (IBM)**, a progressive muscle disease.
- IBM typically affects older adults and causes **asymmetric weakness**, often involving distal muscles, which is not consistent with the patient's presentation.
*Necrotizing vasculitis with granuloma formation*
- This describes conditions like **Granulomatosis with Polyangiitis (GPA)**, which primarily affects **small and medium-sized blood vessels**, often involving the upper and lower respiratory tracts and kidneys.
- While it can cause muscle weakness due to vasculitic neuropathy or myopathy, it does not typically present with the specific "improvement with exercise" seen in this patient, and the presentation is not consistent with LEMS.
*Reduced number of available postsynaptic acetylcholine receptors*
- This is the underlying mechanism for **myasthenia gravis (MG)**, another autoimmune neuromuscular junction disorder.
- While MG also causes fluctuating weakness and ptosis, its weakness typically **worsens with activity** and improves with rest, the opposite of the waxing and waning seen in LEMS.
Question 507: A 50-year-old woman comes to the physician for the evaluation of excessive hair growth on her chin over the past 2 weeks. She also reports progressive enlargement of her gums. Three months ago, she underwent a liver transplantation due to Wilson disease. Following the procedure, the patient was started on transplant rejection prophylaxis. She has a history of poorly-controlled type 2 diabetes mellitus. Temperature is 37°C (98.6°F), pulse is 80/min, respirations are 22/min, and blood pressure is 150/80 mm Hg. Physical examination shows dark-pigmented, coarse hair on the chin, upper lip, and chest. The gingiva and the labial mucosa are swollen. There is a well-healed scar on her right lower abdomen. Which of the following drugs is the most likely cause of this patient's findings?
A. Daclizumab
B. Cyclosporine (Correct Answer)
C. Sirolimus
D. Methotrexate
E. Tacrolimus
Explanation: **Cyclosporine**
* This patient's **combination of hirsutism** (excessive hair growth) **and gingival hyperplasia** (gum enlargement) is the classic presentation of cyclosporine toxicity, an immunosuppressant commonly used for transplant rejection prophylaxis.
* Cyclosporine is a **calcineurin inhibitor** that prevents T-cell activation and is highly effective in preventing graft rejection.
* The **simultaneous presence of both hirsutism and prominent gingival hyperplasia** is particularly characteristic of cyclosporine.
*Daclizumab*
* **Daclizumab** is a **monoclonal antibody** targeting the IL-2 receptor, which was previously used for transplant prophylaxis but has been discontinued for this indication.
* It is not associated with hirsutism or gingival hyperplasia.
*Sirolimus*
* **Sirolimus** is an **mTOR inhibitor** used as an immunosuppressant, known for side effects like hyperlipidemia, myelosuppression, and delayed wound healing.
* It does **not** typically cause hirsutism or gingival hyperplasia.
*Methotrexate*
* **Methotrexate** is an **antimetabolite** and immunosuppressant commonly used in autoimmune diseases and cancer, with side effects including bone marrow suppression, mucositis, and liver toxicity.
* Hirsutism and gingival hyperplasia are **not** characteristic side effects of methotrexate.
*Tacrolimus*
* **Tacrolimus** is another **calcineurin inhibitor**, similar to cyclosporine, but with a different side effect profile. While tacrolimus can cause hirsutism, **gingival hyperplasia is significantly less common** with tacrolimus compared to cyclosporine.
* The **presence of prominent gingival hyperplasia alongside hirsutism strongly favors cyclosporine** over tacrolimus.
* Tacrolimus is more commonly associated with **neurotoxicity** (e.g., tremor) and **nephrotoxicity**.
Question 508: A 54-year-old man comes to the emergency department because of episodic palpitations for the past 12 hours. He has no chest pain. He has coronary artery disease and type 2 diabetes mellitus. His current medications include aspirin, insulin, and atorvastatin. His pulse is 155/min and blood pressure is 116/77 mm Hg. Physical examination shows no abnormalities. An ECG shows monomorphic ventricular tachycardia. An amiodarone bolus and infusion is given, and the ventricular tachycardia converts to normal sinus rhythm. He is discharged home with oral amiodarone. Which of the following is the most likely adverse effect associated with long-term use of this medication?
A. Angle-closure glaucoma
B. Hepatic adenoma
C. Shortened QT interval on ECG
D. Progressive multifocal leukoencephalopathy
E. Chronic interstitial pneumonitis (Correct Answer)
Explanation: ***Chronic interstitial pneumonitis***
- **Amiodarone** is known to cause several dose-dependent adverse effects, including **pulmonary toxicity** in the form of **interstitial pneumonitis** or fibrosis.
- This adverse effect can manifest as progressive dyspnea, cough, and infiltrates on chest imaging, requiring careful monitoring during long-term use.
*Angle-closure glaucoma*
- While some medications can cause **angle-closure glaucoma**, it is **not a classic or common adverse effect of amiodarone**.
- **Topiramate** and **sulfonamides** are more commonly associated with acute angle-closure glaucoma.
*Hepatic adenoma*
- **Hepatic adenomas** are typically associated with **oral contraceptive use** and sometimes **anabolic steroid use**, not amiodarone.
- Amiodarone can cause **hepatic toxicity** (elevated transaminases, hepatitis), but not specifically hepatic adenoma.
*Shortened QT interval on ECG*
- **Amiodarone** is a Class III antiarrhythmic drug that **prolongs the QT interval** by blocking potassium channels, which is its mechanism of action for suppressing arrhythmias.
- Therefore, a shortened QT interval is the **opposite of what would be expected with amiodarone use**.
*Progressive multifocal leukoencephalopathy*
- **Progressive multifocal leukoencephalopathy (PML)** is a rare, severe opportunistic infection of the brain caused by the **JC virus**, typically seen in immunocompromised individuals.
- It is **not an adverse effect of amiodarone**; drugs like natalizumab or rituximab, which affect the immune system, are associated with PML.
Question 509: A 34-year-old female presents to the emergency room with headache and palpitations. She is sweating profusely and appears tremulous on exam. Vital signs are as follows: HR 120, BP 190/110, RR 18, O2 99% on room air, and Temp 37C. Urinary metanephrines and catechols are positive. Which of the following medical regimens is contraindicated as a first-line therapy in this patient?
A. Labetalol
B. Propranolol (Correct Answer)
C. Nitroprusside
D. Lisinopril
E. Phenoxybenzamine
Explanation: ***Propranolol***
- This patient's presentation with headache, palpitations, sweating, hypertension, and tachycardia, along with elevated urinary metanephrines and catechols, is highly suggestive of a **pheochromocytoma**.
- **Pure beta-blockers** (like propranolol) are **absolutely contraindicated** as first-line therapy because blocking $\beta_2$ receptors without initial $\alpha$-blockade leads to unopposed $\alpha$-adrenergic stimulation, causing severe **vasoconstriction** and a dangerous **hypertensive crisis**.
- This is the **most contraindicated** option among the choices listed.
*Labetalol*
- Labetalol is a **non-selective $\beta$-blocker with some $\alpha_1$-blocking activity** (β:α blockade ratio ~7:1).
- While **not recommended** as first-line monotherapy in pheochromocytoma due to predominant beta-blockade, it has **some alpha-blocking properties** that distinguish it from pure beta-blockers.
- In practice, it's typically avoided as initial therapy, but it carries **less risk** than pure beta-blockers because of its partial alpha-blockade.
- Some sources consider it relatively contraindicated, but propranolol (pure beta-blocker) is more definitively contraindicated.
*Nitroprusside*
- **Nitroprusside** is a potent **vasodilator** that acts on both arterial and venous beds, making it effective for **rapid blood pressure reduction** in hypertensive emergencies.
- It is **not contraindicated** and can be used in a pheochromocytoma crisis for acute blood pressure control, though it should ideally be combined with alpha-blockade.
- It does not directly address catecholamine effects but provides symptomatic BP control.
*Lisinopril*
- **Lisinopril** is an **ACE inhibitor**, which works by preventing the conversion of angiotensin I to angiotensin II, leading to vasodilation and reduced aldosterone secretion.
- It is **not contraindicated** but is **inappropriate** as first-line therapy in pheochromocytoma crisis because it does not directly counteract the massive catecholamine release.
- It would be ineffective for managing the acute hypertensive emergency.
*Phenoxybenzamine*
- **Phenoxybenzamine** is an **irreversible, non-selective $\alpha$-adrenergic blocker** that is the **gold standard first-line therapy** for pheochromocytoma.
- It effectively blocks the vasoconstrictive effects of catecholamines, allowing for adequate blood pressure control before any $\beta$-blockade is considered.
- This is the **correct first-line medication**, not contraindicated.
Question 510: A 3-year-old toddler was rushed to the emergency department after consuming peanut butter crackers at daycare. The daycare staff report that the patient has a severe allergy to peanut butter and he was offered the crackers by mistake. The patient is in acute distress. The vital signs include: blood pressure 60/40 mm Hg and heart rate 110/min. There is audible inspiratory stridor and the respiratory rate is 27/min. Upon examination, his chest is covered in a maculopapular rash. Intubation is attempted and failed due to extensive laryngeal edema. The decision for cricothyrotomy is made. Which of the following is the most likely mechanism of this pathology?
A. C3b interaction
B. Deposition of antigen-antibody complexes
C. C5a production
D. IL-2 secretion
E. Mast cell degranulation and histamine release (Correct Answer)
Explanation: ***Mast cell degranulation and histamine release***
- The clinical scenario describes **anaphylaxis**, a severe, life-threatening allergic reaction, which is predominantly mediated by **IgE antibodies** binding to mast cells and basophils.
- Upon re-exposure to the allergen (**peanut butter**), the allergen cross-links IgE molecules on the cell surface, leading to rapid **mast cell degranulation** and the release of preformed mediators like **histamine**, tryptase, and newly synthesized mediators like leukotrienes and prostaglandins. These mediators cause vasodilation, increased vascular permeability (leading to hypotension and edema), bronchoconstriction (leading to stridor), and pruritus/rash.
*C3b interaction*
- **C3b** is a component of the **complement system** and primarily functions in **opsonization** and the formation of the membrane attack complex (MAC).
- While the complement system can be activated in allergic reactions, C3b interaction itself is not the primary mechanism responsible for the acute, severe symptoms of anaphylaxis.
*Deposition of antigen-antibody complexes*
- This mechanism describes a **Type III hypersensitivity reaction** (e.g., serum sickness, lupus nephritis), where immune complexes deposit in tissues leading to inflammation.
- The symptoms described (acute respiratory distress, hypotension, stridor, rash) are characteristic of a **Type I hypersensitivity reaction** mediated by IgE, not immune complex deposition.
*C5a production*
- **C5a** is a powerful **anaphylatoxin** and chemoattractant produced during **complement activation**.
- While C5a can contribute to some features of anaphylaxis by promoting mast cell degranulation, it is a downstream mediator and not the primary initiating mechanism of IgE-mediated anaphylaxis.
*IL-2 secretion*
- **IL-2** (interleukin-2) is a cytokine primarily involved in the **proliferation and differentiation of T cells**, particularly in **cell-mediated immunity** (Type IV hypersensitivity reactions) and immune regulation.
- It does not play a direct, immediate role in the acute mast cell degranulation and mediator release characteristic of anaphylaxis.
