A 57-year-old woman presents to the emergency department with acute onset confusion, sweating, weakness, and tremors. She says that the symptoms started when she went to dinner with friends and had several drinks of alcohol without eating much food. Her past medical history is significant for type 2 diabetes, and she was recently started on a new medication for this disease. She mentions that her doctor warned her about the risk of low blood sugar, especially if she drinks alcohol or skips meals. Which of the following describes the mechanism of action for the most likely diabetes drug that this patient started taking?
Q942
A 55-year-old man presents to his physician with a complaint of recurrent episodes of palpitations over the past 2 weeks. He also mentions that he tends to tire easily. He denies chest pain, breathlessness, dizziness, or syncope, but has a history of ischemic heart disease. He smokes 1 pack of cigarettes every day and drinks alcohol occasionally. The physical examination revealed a temperature of 36.9°C (98.4°F), a pulse of 124/min (irregular), a blood pressure of 142/86 mm Hg, and a respiratory rate of 16/min. Auscultation of his chest is normal with an absence of rales overall lung fields. An ECG was significant for fibrillatory waves and an irregular RR interval. Thus, the physician concludes that the symptoms are due to atrial fibrillation. The patient is prescribed oral diltiazem. Which of the following side effects should the physician warn the patient about?
Q943
A 9-year-old boy presents for incision and drainage of a small abscess on his left thigh. No significant past medical history. No current medications. Before the procedure, the patient is allowed to inhale colorless, sweet-smelling gas. After the procedure, the patient receives 3–4 minutes of high flow oxygen through a nasal mask. The pulse oximetry shows an oxygen saturation of 94%. This patient was oxygenated at the end of the procedure to prevent which of the following complications?
Q944
A 28-year-old woman comes to the physician for a follow-up examination. Two months ago, she underwent left renal transplantation for recurrent glomerulonephritis. At the time of discharge, her creatinine was 0.9 mg/dL. She feels well. Current medications include tacrolimus and azathioprine. Her pulse is 85/min and blood pressure is 135/75 mmHg. Physical examination shows a well-healed surgical scar on her left lower abdomen. The remainder of the examination shows no abnormalities. The patient should be monitored for which of the following adverse effects of her medications?
Q945
A 30-year-old woman presents for pregnancy counseling. She says she has an 8-week history of chronic diarrhea. She is also found to be intolerant to heat and has been significantly losing her hair. She denies any recent changes to her diet. The patient is afebrile and her vital signs are within normal limits. Her weight today is 45.0 kg (99.2 lb) which is 4.5 kg (10 lb) less than her weight during her last visit 2 months back. On physical examination, the patient is anxious and has a non-intention tremor. Significant exophthalmos is present. Laboratory findings are significant for a low TSH, elevated free T4 and free T3, and a positive thyroid stimulating immunoglobulin assay. She still wants to conceive a baby and asks for an appropriate treatment that is safe in pregnancy. Which of the following best describes the therapy she will most likely receive during her pregnancy for her thyroid disorder?
Q946
A 70-year-old man is brought to the emergency department with complaints of chest pain for the last 2 hours. He had been discharged from the hospital 10 days ago when he was admitted for acute myocardial infarction. It was successfully treated with percutaneous coronary intervention. During the physical exam, the patient prefers to hunch forwards as this decreases his chest pain. He says the pain is in the middle of the chest and radiates to his back. Despite feeling unwell, the patient denies any palpitations or shortness of breath. Vitals signs include: pulse 90/min, respiratory rate 20/min, blood pressure 134/82 mm Hg, and temperature 36.8°C (98.2°F). The patient is visibly distressed and is taking shallow breaths because deeper breaths worsen his chest pain. An ECG shows diffuse ST elevations. Which of the following should be administered to this patient?
Q947
A 69-year-old man comes to his cardiologist for a follow-up visit. He is being considered for a new drug therapy that works by modulating certain proteins released from the heart in patients with heart failure. A drug called candoxatril is being investigated for its ability to inhibit the action of an endopeptidase that breaks down a vasodilatory mediator released from the heart, as well as, endothelin and bradykinin. This mediator is known to promote the excretion of sodium from the body and improve the ejection fraction. One of its side effects is its ability to increase angiotensin II levels which causes harm to patients with heart failure. Therefore, to improve efficacy and reduce its adverse effects, candoxatril has to be used in conjunction with angiotensin receptor blockers. Which of the following is most likely to increase as a result of this drug regimen?
Q948
A 25-year-old woman is rushed to the emergency department after she was found unconscious in a house fire. She has no previous medical history available. At the hospital, the vital signs include: blood pressure 110/70 mm Hg, temperature 36.0°C (97.0°F), and heart rate 76/min with oxygen saturation 99% on room air. On physical exam she is unconscious. There are superficial burns on her hands and parts of her face. Her face and clothes are blackened with soot. What is the 1st best step while treating this patient?
Q949
A 59-year-old male presents to the emergency room complaining of substernal chest pain. He reports a three-hour history of dull substernal chest pain that radiates into his left arm and jaw. He has experienced similar chest pain before that was brought on with exertion, but this pain is more severe and occurred with rest. His past medical history includes gout, hypertension, diabetes mellitus, and hyperlipidemia. An EKG demonstrates ST segment depression. Serum troponin is elevated. In addition to aspirin, oxygen, and morphine, he is started on a sublingual medication. What is the main physiologic effect of this medication?
Q950
A 17-year-old male presents with altered mental status. He was recently admitted to the hospital due to a tibial fracture suffered while playing soccer. His nurse states that he is difficult to arouse. His temperature is 98.6 deg F (37 deg C), blood pressure is 130/80 mm Hg, pulse is 60/min, and respirations are 6/min. Exam is notable for pinpoint pupils and significant lethargy. Which of the following describes the mechanism of action of the drug likely causing this patient's altered mental status?
Autonomic/CV Drugs US Medical PG Practice Questions and MCQs
Question 941: A 57-year-old woman presents to the emergency department with acute onset confusion, sweating, weakness, and tremors. She says that the symptoms started when she went to dinner with friends and had several drinks of alcohol without eating much food. Her past medical history is significant for type 2 diabetes, and she was recently started on a new medication for this disease. She mentions that her doctor warned her about the risk of low blood sugar, especially if she drinks alcohol or skips meals. Which of the following describes the mechanism of action for the most likely diabetes drug that this patient started taking?
A. Inhibiting dipeptidyl peptidase
B. Closing potassium channels (Correct Answer)
C. Inhibiting alpha-glucosidase
D. Decreasing hepatic gluconeogenesis
E. Binding to peroxisome proliferator-activating receptors
Explanation: ***Closing potassium channels***
The patient's symptoms (confusion, sweating, weakness, tremors) along with recent alcohol consumption and a new diabetes medication strongly suggest **hypoglycemia**. **Sulfonylureas** are a class of diabetes drugs known to cause hypoglycemia, especially with alcohol, by binding to and **closing ATP-sensitive potassium channels** on pancreatic beta cells, leading to depolarization and insulin release. The doctor's warning about hypoglycemia risk with alcohol or skipped meals is classic for sulfonylureas.
*Inhibiting dipeptidyl peptidase*
This mechanism describes **DPP-4 inhibitors** (gliptins), which increase levels of endogenous incretins (GLP-1 and GIP) by preventing their breakdown. These drugs have a **low risk of hypoglycemia** when used alone because they work in a glucose-dependent manner. They do not typically cause severe hypoglycemia, especially not to the extent described in this case.
*Inhibiting alpha-glucosidase*
Alpha-glucosidase inhibitors (e.g., **acarbose**, miglitol) delay carbohydrate absorption in the small intestine by inhibiting brush border enzymes. While they can cause gastrointestinal side effects (flatulence, diarrhea), they have a **very low risk of hypoglycemia** because they do not affect insulin secretion directly.
*Decreasing hepatic gluconeogenesis*
This is the primary mechanism of action for **metformin**, which is a biguanide and typically the first-line agent for type 2 diabetes. Metformin reduces glucose production by the liver and has a **very low risk of hypoglycemia** when used as monotherapy, making it an unlikely cause of the patient's acute symptoms.
*Binding to peroxisome proliferator-activating receptors*
This mechanism describes **thiazolidinediones** (TZDs) like pioglitazone and rosiglitazone, which improve insulin sensitivity by activating PPAR-gamma receptors. They typically have a **low risk of hypoglycemia** when used as monotherapy. Their common side effects include weight gain, fluid retention, and increased fracture risk—not acute hypoglycemia.
Question 942: A 55-year-old man presents to his physician with a complaint of recurrent episodes of palpitations over the past 2 weeks. He also mentions that he tends to tire easily. He denies chest pain, breathlessness, dizziness, or syncope, but has a history of ischemic heart disease. He smokes 1 pack of cigarettes every day and drinks alcohol occasionally. The physical examination revealed a temperature of 36.9°C (98.4°F), a pulse of 124/min (irregular), a blood pressure of 142/86 mm Hg, and a respiratory rate of 16/min. Auscultation of his chest is normal with an absence of rales overall lung fields. An ECG was significant for fibrillatory waves and an irregular RR interval. Thus, the physician concludes that the symptoms are due to atrial fibrillation. The patient is prescribed oral diltiazem. Which of the following side effects should the physician warn the patient about?
A. Stevens-Johnson syndrome
B. Bloody diarrhea
C. Hypoglycemia
D. Bilateral pedal edema (Correct Answer)
E. Multifocal atrial tachycardia
Explanation: ***Bilateral pedal edema***
- **Diltiazem**, a **calcium channel blocker**, can cause **peripheral vasodilation**, leading to fluid extravasation and **bilateral pedal edema**.
- This is a common and dose-dependent side effect, typically managed by dose reduction or switching to another agent if bothersome.
*Stevens-Johnson syndrome*
- This is a severe, life-threatening **cutaneous adverse drug reaction** characterized by widespread blistering and epidermal detachment, commonly associated with drugs like **antibiotics (sulfonamides)** or **anticonvulsants**.
- It is **not a typical side effect of diltiazem**, although rare idiosyncratic reactions to nearly any drug are possible.
*Bloody diarrhea*
- **Bloody diarrhea** is typically associated with **gastrointestinal infections** (e.g., *E. coli* O157:H7, *Shigella* spp.) or inflammatory bowel disease.
- It is **not a known side effect of diltiazem**; diltiazem may cause constipation, not diarrhea.
*Hypoglycemia*
- **Hypoglycemia** is a common side effect of **insulin** or **sulfonylurea medications** used to treat diabetes.
- Diltiazem does **not directly affect blood glucose levels** or cause hypoglycemia.
*Multifocal atrial tachycardia*
- **Multifocal atrial tachycardia (MAT)** is an **arrhythmia** characterized by at least three distinct P wave morphologies and an irregular rhythm.
- **Diltiazem** is used to **treat arrhythmias** like atrial fibrillation and would not typically cause a new, distinct arrhythmia such as MAT.
Question 943: A 9-year-old boy presents for incision and drainage of a small abscess on his left thigh. No significant past medical history. No current medications. Before the procedure, the patient is allowed to inhale colorless, sweet-smelling gas. After the procedure, the patient receives 3–4 minutes of high flow oxygen through a nasal mask. The pulse oximetry shows an oxygen saturation of 94%. This patient was oxygenated at the end of the procedure to prevent which of the following complications?
A. Malignant hyperthermia
B. Hepatotoxicity
C. Raised intracranial pressure
D. Cardiac arrhythmias
E. Diffusion hypoxia (Correct Answer)
Explanation: ***Diffusion hypoxia (Correct)***
- **Nitrous oxide** rapidly diffuses from the blood into the alveoli after discontinuation, displacing oxygen and carbon dioxide.
- This creates the **"Fink effect"** - a dilution of alveolar oxygen that can lead to transient **hypoxemia**.
- Administering **high-flow oxygen for 3-5 minutes** prevents this complication by maintaining adequate alveolar oxygen concentration during the N2O washout period.
*Malignant hyperthermia (Incorrect)*
- This is a pharmacogenetic disorder triggered by **volatile anesthetics** (e.g., halothane, sevoflurane) and **succinylcholine**, not nitrous oxide.
- Characterized by **muscle rigidity, hyperthermia, and hypermetabolism**.
- While oxygen is part of supportive treatment, post-procedure oxygenation doesn't prevent its onset.
- Treatment requires **dantrolene**, not just oxygen.
*Hepatotoxicity (Incorrect)*
- Not prevented by post-procedure oxygenation.
- Typically associated with **halothane** (rare with modern anesthetics), not nitrous oxide.
- Nitrous oxide is not a primary cause of hepatotoxicity.
*Raised intracranial pressure (Incorrect)*
- While nitrous oxide can increase **cerebral blood flow** and potentially raise ICP, post-procedure oxygen doesn't specifically prevent this effect.
- Management of elevated ICP involves **hyperventilation, head elevation, osmotic diuretics**, and avoiding N2O in at-risk patients.
- The oxygen administration here targets diffusion hypoxia, not ICP control.
*Cardiac arrhythmias (Incorrect)*
- While hypoxia can cause arrhythmias, the primary purpose of post-N2O oxygen is to prevent **diffusion hypoxia**.
- Preventing hypoxemia secondarily reduces arrhythmia risk, but this is not the direct indication.
- Arrhythmias from anesthetics are more commonly associated with **halogenated agents** sensitizing the myocardium to catecholamines.
Question 944: A 28-year-old woman comes to the physician for a follow-up examination. Two months ago, she underwent left renal transplantation for recurrent glomerulonephritis. At the time of discharge, her creatinine was 0.9 mg/dL. She feels well. Current medications include tacrolimus and azathioprine. Her pulse is 85/min and blood pressure is 135/75 mmHg. Physical examination shows a well-healed surgical scar on her left lower abdomen. The remainder of the examination shows no abnormalities. The patient should be monitored for which of the following adverse effects of her medications?
A. Gingival hyperplasia
B. Kidney injury (Correct Answer)
C. Polycythemia
D. Hepatic necrosis
E. Bone marrow suppression
Explanation: ***Kidney injury***
- **Tacrolimus** is a potent calcineurin inhibitor that can cause **nephrotoxicity** (kidney injury) by inducing afferent arteriolar vasoconstriction and direct tubular toxicity.
- Close monitoring of **creatinine** and **tacrolimus trough levels** is essential to prevent and detect this adverse effect, especially in renal transplant patients where baseline function must be preserved.
- This is the **most critical monitoring parameter** for tacrolimus therapy.
*Gingival hyperplasia*
- This adverse effect is more commonly associated with **cyclosporine**, another calcineurin inhibitor, rather than tacrolimus.
- While both are immunosuppressants used in transplant, tacrolimus has a lower incidence of this cosmetic side effect.
*Polycythemia*
- Polycythemia is not a typical adverse effect of **tacrolimus** or **azathioprine**.
- Renal transplant patients may sometimes experience erythrocytosis due to increased erythropoietin production from the native kidneys or the transplanted kidney, but it's not directly related to these immunosuppressive medications.
*Hepatic necrosis*
- While **azathioprine** can cause **hepatotoxicity**, it typically manifests as cholestatic injury or dose-dependent hepatitis, rather than acute hepatic necrosis.
- Tacrolimus is not primarily associated with hepatic necrosis.
*Bone marrow suppression*
- **Azathioprine** is an antimetabolite that can cause **myelosuppression** (leukopenia, thrombocytopenia, anemia) by interfering with DNA synthesis.
- While this requires regular **CBC monitoring**, in this clinical scenario, **nephrotoxicity from tacrolimus** is the more immediate concern given the recent renal transplant and the need to preserve graft function.
- The question emphasizes creatinine monitoring (baseline 0.9 mg/dL mentioned), directing focus toward tacrolimus nephrotoxicity as the primary monitoring concern.
Question 945: A 30-year-old woman presents for pregnancy counseling. She says she has an 8-week history of chronic diarrhea. She is also found to be intolerant to heat and has been significantly losing her hair. She denies any recent changes to her diet. The patient is afebrile and her vital signs are within normal limits. Her weight today is 45.0 kg (99.2 lb) which is 4.5 kg (10 lb) less than her weight during her last visit 2 months back. On physical examination, the patient is anxious and has a non-intention tremor. Significant exophthalmos is present. Laboratory findings are significant for a low TSH, elevated free T4 and free T3, and a positive thyroid stimulating immunoglobulin assay. She still wants to conceive a baby and asks for an appropriate treatment that is safe in pregnancy. Which of the following best describes the therapy she will most likely receive during her pregnancy for her thyroid disorder?
A. Beta-blockers
B. Thyroidectomy and thyroid replacement
C. Plasmapheresis
D. Radiation
E. Antithyroid drugs (thionamides) (Correct Answer)
Explanation: ***Antithyroid drugs (thionamides)***
- **Antithyroid drugs** like **propylthiouracil (PTU)** or **methimazole** are the primary treatment for **hyperthyroidism** during pregnancy, as they reduce thyroid hormone synthesis.
- **PTU** is often preferred in the **first trimester** due to a lower risk of teratogenicity compared to methimazole, although **methimazole** can be used in the **second and third trimesters**.
*Beta-blockers*
- **Beta-blockers** can alleviate **symptomatic hyperthyroidism** (e.g., tremor, palpitations) in the short term but do not address the underlying hormonal imbalance.
- They are generally used as **adjunctive therapy** for symptom control, especially in the initial stages, but are not a definitive treatment for the thyroid disorder itself.
*Thyroidectomy and thyroid replacement*
- **Thyroidectomy** is a surgical option for hyperthyroidism, but it is typically reserved for cases where antithyroid medications are ineffective or contraindicated, or in emergencies like **thyroid storm** not responsive to medical therapy.
- **Surgery during pregnancy** carries significant risks to both the mother and the fetus and is generally avoided unless absolutely necessary, usually during the **second trimester** if unavoidable.
*Plasmapheresis*
- **Plasmapheresis** is a procedure used in severe, life-threatening cases of hyperthyroidism, such as **thyroid storm**, particularly when other treatments have failed or are not tolerated.
- It rapidly reduces circulating thyroid hormones and **thyroid-stimulating immunoglobulins (TSI)** but is not a routine or long-term treatment for pregnancy-associated hyperthyroidism.
*Radiation*
- **Radioactive iodine (RAI) therapy** is effective in destroying overactive thyroid tissue and is a common treatment for hyperthyroidism in non-pregnant individuals.
- However, **RAI is absolutely contraindicated in pregnancy** because it can cross the placenta and ablate the fetal thyroid gland, causing **fetal hypothyroidism**.
Question 946: A 70-year-old man is brought to the emergency department with complaints of chest pain for the last 2 hours. He had been discharged from the hospital 10 days ago when he was admitted for acute myocardial infarction. It was successfully treated with percutaneous coronary intervention. During the physical exam, the patient prefers to hunch forwards as this decreases his chest pain. He says the pain is in the middle of the chest and radiates to his back. Despite feeling unwell, the patient denies any palpitations or shortness of breath. Vitals signs include: pulse 90/min, respiratory rate 20/min, blood pressure 134/82 mm Hg, and temperature 36.8°C (98.2°F). The patient is visibly distressed and is taking shallow breaths because deeper breaths worsen his chest pain. An ECG shows diffuse ST elevations. Which of the following should be administered to this patient?
A. Ibuprofen (Correct Answer)
B. Propranolol
C. Levofloxacin
D. Heparin
E. Warfarin
Explanation: ***Ibuprofen***
- This patient presents with symptoms highly suggestive of **post-myocardial infarction (MI) pericarditis**, also known as **Dressler's syndrome**, indicated by recent MI, chest pain relieved by leaning forward, and diffuse ST elevations.
- **NSAIDs like ibuprofen** are the first-line treatment for pericarditis due to their potent anti-inflammatory properties, reducing pain and inflammation.
*Propranolol*
- **Propranolol** is a **beta-blocker** used to reduce heart rate and blood pressure, and manage angina or arrhythmias.
- It is not indicated for the management of **pericarditis**, as it does not address the underlying inflammation.
*Levofloxacin*
- **Levofloxacin** is an **antibiotic** used to treat bacterial infections.
- Pericarditis, especially Dressler's syndrome, is an inflammatory condition, not an infection, so antibiotics are **ineffective**.
*Heparin*
- **Heparin** is an anticoagulant used to prevent blood clot formation, particularly in acute coronary syndromes or pulmonary embolism.
- It is **contraindicated in pericarditis** as it can increase the risk of **hemorrhagic pericardial effusion** or **cardiac tamponade**.
*Warfarin*
- **Warfarin** is an **oral anticoagulant** used for long-term prevention of blood clots in conditions like atrial fibrillation or deep vein thrombosis.
- Similar to heparin, **anticoagulation with warfarin is contraindicated in pericarditis** due to the increased risk of potentially life-threatening bleeding into the pericardial space.
Question 947: A 69-year-old man comes to his cardiologist for a follow-up visit. He is being considered for a new drug therapy that works by modulating certain proteins released from the heart in patients with heart failure. A drug called candoxatril is being investigated for its ability to inhibit the action of an endopeptidase that breaks down a vasodilatory mediator released from the heart, as well as, endothelin and bradykinin. This mediator is known to promote the excretion of sodium from the body and improve the ejection fraction. One of its side effects is its ability to increase angiotensin II levels which causes harm to patients with heart failure. Therefore, to improve efficacy and reduce its adverse effects, candoxatril has to be used in conjunction with angiotensin receptor blockers. Which of the following is most likely to increase as a result of this drug regimen?
A. Acetylcholine
B. Natriuretic peptides (Correct Answer)
C. Leukotrienes
D. Nitric oxide
E. Thromboxane
Explanation: ***Natriuretic peptides***
- **Candoxatril** inhibits **neprilysin**, an endopeptidase that breaks down **natriuretic peptides**. Therefore, inhibiting this enzyme leads to increased levels of natriuretic peptides, which have vasodilatory and natriuretic effects.
- The medication regimen described, which involves inhibiting the breakdown of a vasodilatory mediator released from the heart and simultaneously blocking angiotensin II, is consistent with the mechanism of action of **sacubitril/valsartan**, where **sacubitril** is a **neprilysin inhibitor** that increases natriuretic peptide levels.
*Acetylcholine*
- **Acetylcholine** is a neurotransmitter involved in parasympathetic nervous system activity and has no direct relationship with the described drug mechanism of inhibiting neprilysin or blocking angiotensin II.
- Its levels would not be directly increased by the action of **candoxatril** (neprilysin inhibitor) or an **angiotensin receptor blocker**.
*Leukotrienes*
- **Leukotrienes** are inflammatory mediators derived from arachidonic acid and are primarily involved in allergic and inflammatory responses.
- Their synthesis and degradation pathways are distinct from those affected by **neprilysin inhibition** or **angiotensin receptor blockade**.
*Nitric oxide*
- **Nitric oxide** is a potent vasodilator produced by endothelial cells, but its levels are not directly increased by inhibiting **neprilysin**.
- While natriuretic peptides can indirectly influence nitric oxide production, **candoxatril**'s primary effect is on natriuretic peptide metabolism.
*Thromboxane*
- **Thromboxane** is a prostaglandin that causes vasoconstriction and platelet aggregation. Its synthesis is primarily inhibited by NSAIDs like aspirin.
- Its levels would not be directly affected by the described drug regimen targeting **neprilysin** and the **renin-angiotensin system**.
Question 948: A 25-year-old woman is rushed to the emergency department after she was found unconscious in a house fire. She has no previous medical history available. At the hospital, the vital signs include: blood pressure 110/70 mm Hg, temperature 36.0°C (97.0°F), and heart rate 76/min with oxygen saturation 99% on room air. On physical exam she is unconscious. There are superficial burns on her hands and parts of her face. Her face and clothes are blackened with soot. What is the 1st best step while treating this patient?
A. Sodium nitrite
B. Administer 100% oxygen (Correct Answer)
C. Penicillamine
D. Pyridoxine (vitamin B6)
E. N-acetylcysteine
Explanation: ***Administer 100% oxygen***
- The patient's presentation with **soot on her face and clothes**, and unconsciousness after a house fire, strongly suggests **carbon monoxide (CO) poisoning** and potential **cyanide poisoning**.
- **100% oxygen** is the first-line treatment for CO poisoning, as it rapidly displaces CO from hemoglobin and accelerates its elimination.
*Sodium nitrite*
- Sodium nitrite is used to treat **cyanide poisoning** by inducing methemoglobinemia, which then binds to cyanide.
- While cyanide poisoning is possible in house fires, **CO poisoning is more immediate and life-threatening** in terms of respiratory compromise.
*Penicillamine*
- Penicillamine is a **chelating agent** used primarily for **copper poisoning** (e.g., Wilson's disease) or severe lead poisoning.
- It has no role in the immediate treatment of smoke inhalation or carbon monoxide poisoning.
*Pyridoxine (vitamin B6)*
- Pyridoxine is the antidote for **isoniazid overdose** and can be used for **ethylene glycol poisoning**.
- It is not indicated for the management of smoke inhalation or carbon monoxide poisoning.
*N-acetylcysteine*
- N-acetylcysteine is the antidote for **acetaminophen (paracetamol) overdose** and is also used as a mucolytic.
- It is not indicated for the immediate treatment of smoke inhalation or carbon monoxide poisoning.
Question 949: A 59-year-old male presents to the emergency room complaining of substernal chest pain. He reports a three-hour history of dull substernal chest pain that radiates into his left arm and jaw. He has experienced similar chest pain before that was brought on with exertion, but this pain is more severe and occurred with rest. His past medical history includes gout, hypertension, diabetes mellitus, and hyperlipidemia. An EKG demonstrates ST segment depression. Serum troponin is elevated. In addition to aspirin, oxygen, and morphine, he is started on a sublingual medication. What is the main physiologic effect of this medication?
A. Decrease preload (Correct Answer)
B. Decrease heart rate
C. Increase contractility
D. Increase preload
E. Decrease afterload
Explanation: ***Decrease preload***
- The sublingual medication is likely **nitroglycerin**, which primarily acts as a **venodilator**.
- **Venodilation** leads to pooling of blood in the peripheral veins, thereby reducing the amount of blood returning to the heart, which in turn **decreases preload**.
*Decrease heart rate*
- While medications like **beta-blockers** decrease heart rate, nitroglycerin's primary effect is not heart rate reduction.
- A decreased heart rate reduces myocardial oxygen demand, but this is not the main physiologic effect of sublingual nitroglycerin in an acute setting.
*Increase contractility*
- Increasing contractility would **raise myocardial oxygen demand**, which is counterproductive in a patient experiencing myocardial ischemia.
- Medications that increase contractility, such as **inotropes**, are generally avoided in acute coronary syndromes unless there is severe heart failure.
*Increase preload*
- Increasing preload would **increase myocardial oxygen demand** and potentially exacerbate the patient's ischemic symptoms.
- In acute coronary syndrome, the goal is to reduce cardiac workload to re-establish the balance between oxygen supply and demand.
*Decrease afterload*
- While nitroglycerin can cause some **arterial dilation** and thus decrease afterload, its predominant effect at standard doses for acute chest pain is **venodilation**, leading to a greater reduction in preload.
- Decreasing afterload also helps reduce myocardial oxygen demand but is a secondary effect compared to preload reduction.
Question 950: A 17-year-old male presents with altered mental status. He was recently admitted to the hospital due to a tibial fracture suffered while playing soccer. His nurse states that he is difficult to arouse. His temperature is 98.6 deg F (37 deg C), blood pressure is 130/80 mm Hg, pulse is 60/min, and respirations are 6/min. Exam is notable for pinpoint pupils and significant lethargy. Which of the following describes the mechanism of action of the drug likely causing this patient's altered mental status?
A. Neuronal hyperpolarization due to sodium influx
B. Neuronal depolarization due to sodium efflux
C. Neuronal depolarization due to potassium influx
D. Neuronal hyperpolarization due to potassium efflux (Correct Answer)
E. Neuronal hyperpolarization due to chloride influx
Explanation: ***Neuronal hyperpolarization due to potassium efflux***
- The patient's symptoms of **altered mental status**, **pinpoint pupils**, and **respiratory depression** are classic for **opioid overdose**.
- Opioids act by binding to opioid receptors (mu, delta, kappa), which are **G-protein coupled receptors**. Activation of these receptors leads to **potassium efflux** and **calcium influx inhibition**, causing neuronal hyperpolarization and reduced neuronal excitability.
*Neuronal hyperpolarization due to sodium influx*
- **Sodium influx** typically causes depolarization, not hyperpolarization, making this option inconsistent with the mechanism of inducing neuronal inhibition.
- Hyperpolarization usually involves outward positive current (like potassium efflux) or inward negative current (like chloride influx).
*Neuronal depolarization due to sodium efflux*
- **Sodium efflux** (e.g., via the Na+/K+-ATPase) is crucial for maintaining resting membrane potential, but it does not directly lead to depolarization as described here.
- Depolarization is commonly associated with **sodium influx**, not efflux, causing the membrane potential to become more positive.
*Neuronal depolarization due to potassium influx*
- **Potassium influx** would make the cell less negative inside (depolarization), but this is not the primary mechanism of action for opioids.
- Opioids primarily cause **hyperpolarization** and reduced excitability, making this mechanism incorrect for the observed clinical picture caused by opioid overdose.
*Neuronal hyperpolarization due to chloride influx*
- While **chloride influx** does cause neuronal hyperpolarization (e.g., via GABA-A receptor activation by benzodiazepines), this is the mechanism for **GABAergic drugs**, not opioids.
- Opioids primarily achieve hyperpolarization through **potassium efflux**.
