All questions
Question 1
A 45-year-old agricultural worker is brought to the emergency department by his coworkers. He is confused, sweating profusely, and has difficulty breathing. Physical examination reveals pinpoint pupils, diffuse muscle fasciculations, and wheezing on lung auscultation. He is diagnosed with organophosphate poisoning. He is intubated and treated with atropine.
In addition to atropine, which of the following medications should be administered to regenerate the affected enzyme and treat the nicotinic effects?
- Edrophonium
- Physostigmine
- Pralidoxime (correct answer)
- Neostigmine
Explanation: Organophosphates are irreversible acetylcholinesterase inhibitors. Atropine is a muscarinic antagonist that competitively blocks the effects of excess acetylcholine at muscarinic receptors, treating symptoms like bradycardia, salivation, and bronchospasm. However, it has no effect on nicotinic receptors (responsible for muscle fasciculations and weakness). Pralidoxime is a cholinesterase reactivator that removes the organophosphate from the enzyme, restoring its function. It must be given early, before the bond 'ages'.
Question 2
A 6-year-old boy is brought to the emergency department after his mother found him eating berries from a plant in their garden, identified as Atropa belladonna (deadly nightshade). The child is agitated, has a high fever, flushed skin, dry mucous membranes, and markedly dilated pupils. His heart rate is 160/min.
This patient's toxidrome is caused by the antagonism of which of the following receptors?
- Muscarinic cholinergic receptors (correct answer)
- Nicotinic cholinergic receptors
- Alpha-adrenergic receptors
- Beta-adrenergic receptors
Explanation: The patient is presenting with classic anticholinergic (antimuscarinic) toxicity, often remembered by the mnemonic 'hot as a hare, blind as a bat, dry as a bone, red as a beet, mad as a hatter.' The toxins in Atropa belladonna, such as atropine and scopolamine, are potent competitive antagonists of muscarinic cholinergic receptors, leading to inhibition of parasympathetic functions.
Question 3
A 58-year-old woman is prescribed oxybutynin for treatment of overactive bladder. She reports significant improvement in her symptoms of urinary urgency and frequency. However, she contacts her physician a month later complaining of a persistently bothersome side effect.
Based on the mechanism of action of oxybutynin, which of the following side effects is she most likely experiencing?
- Diarrhea
- Bradycardia
- Excessive tearing
- Dry mouth (correct answer)
Explanation: Oxybutynin is an antimuscarinic agent that blocks M3 receptors on the detrusor muscle, causing it to relax and increasing bladder capacity. However, it also blocks muscarinic receptors elsewhere in the body, leading to classic anticholinergic side effects. These include dry mouth (xerostomia) due to blockade of M3 receptors on salivary glands, constipation, blurred vision, and confusion, especially in the elderly.
Question 4
A 55-year-old man is in the intensive care unit with septic shock. Despite aggressive intravenous fluid resuscitation, his mean arterial pressure remains low at 55 mm Hg. A continuous infusion of phenylephrine is initiated, which successfully increases his blood pressure.
The therapeutic effect of phenylephrine in this patient is mediated primarily by the stimulation of which of the following receptors?
- Alpha-1 adrenergic (correct answer)
- Beta-1 adrenergic
- Beta-2 adrenergic
- Dopamine D1
Explanation: Phenylephrine is a selective alpha-1 adrenergic agonist. Activation of alpha-1 receptors on vascular smooth muscle causes potent vasoconstriction, which increases systemic vascular resistance (SVR) and, consequently, blood pressure. It has minimal effect on beta receptors, so it does not directly increase heart rate or contractility and may cause a reflex bradycardia.
Question 5
A 59-year-old man with a history of resistant hypertension is prescribed clonidine. His blood pressure improves significantly after starting the medication. The physician cautions him against abruptly discontinuing the drug due to the risk of rebound hypertension.
What is the primary mechanism by which clonidine exerts its antihypertensive effect?
- Blockade of alpha-1 receptors in peripheral arterioles
- Stimulation of central presynaptic alpha-2 receptors (correct answer)
- Blockade of beta-1 receptors in the juxtaglomerular apparatus
- Direct relaxation of vascular smooth muscle via nitric oxide
Explanation: Clonidine is a centrally acting alpha-2 adrenergic agonist. It stimulates alpha-2 receptors in the brainstem (specifically the nucleus tractus solitarii), which inhibits presynaptic release of norepinephrine. This leads to a decrease in central sympathetic outflow, reducing heart rate, cardiac output, and peripheral vascular resistance, thereby lowering blood pressure.
Question 6
A 70-year-old woman with a history of ischemic cardiomyopathy is admitted with acute decompensated heart failure and cardiogenic shock. Her blood pressure is 80/50 mm Hg, and she has signs of poor organ perfusion. An infusion of dobutamine is started.
The primary desired hemodynamic effect of dobutamine in this patient is an increase in which of the following?
- Systemic vascular resistance
- Myocardial contractility (correct answer)
- Pulmonary capillary wedge pressure
- Afterload
Explanation: Dobutamine is a synthetic catecholamine that is primarily a beta-1 adrenergic agonist. Stimulation of beta-1 receptors in the heart leads to a significant increase in myocardial contractility (positive inotropy) and, to a lesser extent, heart rate. This improves cardiac output and organ perfusion in cardiogenic shock. Dobutamine also has weak beta-2 agonist activity, which can cause mild vasodilation and a decrease in systemic vascular resistance (afterload).
Question 7
A 19-year-old college student with a history of intermittent asthma reports using his albuterol inhaler 4-5 times a day for the past week due to wheezing. He tells his physician that after each use, he feels his 'heart racing' and his hands get 'shaky'.
These adverse effects are best explained by albuterol's stimulation of which of the following receptors?
- Beta-2 receptors in skeletal muscle and cardiac tissue (correct answer)
- Alpha-1 receptors in peripheral vasculature
- Muscarinic M2 receptors in the sinoatrial node
- Beta-1 receptors in the kidney
Explanation: Albuterol is a short-acting beta-2 selective adrenergic agonist used for bronchodilation. However, at higher doses or with frequent use, its selectivity decreases. The tremor (shaky hands) results from stimulation of beta-2 receptors in skeletal muscle. The tachycardia (heart racing) occurs due to stimulation of both beta-2 receptors present in cardiac tissue and some cross-reactivity with cardiac beta-1 receptors at higher doses.
Question 8
A 62-year-old man is started on prazosin for symptomatic benign prostatic hyperplasia. On the second day of treatment, he feels dizzy and nearly faints upon standing up from his bed in the morning.
This patient's symptoms are most likely due to which of the following effects of the medication?
- Reflex tachycardia
- First-dose orthostatic hypotension (correct answer)
- Central nervous system sedation
- Drug-induced bradycardia
Explanation: Prazosin is an alpha-1 adrenergic antagonist. It blocks alpha-1 receptors on both arterial and venous smooth muscle, causing vasodilation and a decrease in blood pressure. A well-known adverse effect, particularly with the first dose or after a dose increase, is orthostatic hypotension. This occurs because the blockade of venous alpha-1 receptors prevents the normal vasoconstrictor response needed to maintain blood pressure upon standing.
Question 9
A 67-year-old man with chronic systolic heart failure (ejection fraction 30%) is being managed with an ACE inhibitor, a diuretic, and carvedilol. Studies have shown that carvedilol improves long-term survival in patients with heart failure.
The unique therapeutic benefit of carvedilol in this condition is derived from its antagonist activity at which combination of receptors?
- Beta-1 and Beta-2 only
- Beta-1 only
- Alpha-1, Beta-1, and Beta-2 (correct answer)
- Muscarinic M2 and Beta-1
Explanation: Carvedilol (and labetalol) are non-selective beta-blockers that also have alpha-1 blocking properties. In heart failure, the beta-1 blockade reduces the harmful effects of chronic sympathetic stimulation on the heart (e.g., remodeling, apoptosis). The alpha-1 blockade causes peripheral vasodilation, which reduces both preload and afterload, further decreasing the workload on the failing heart.
Question 10
A 28-year-old woman is prescribed a transdermal patch to prevent motion sickness during an upcoming cruise. The medication is highly effective but she notes side effects of drowsiness and a dry mouth.
The medication in the patch, most likely scopolamine, exerts its antiemetic effect by blocking which class of receptors in the central nervous system?
- Serotonin 5-HT3 receptors
- Histamine H1 receptors
- Dopamine D2 receptors
- Muscarinic cholinergic receptors (correct answer)
Explanation: Scopolamine is a centrally acting antimuscarinic agent. It is particularly effective for motion sickness because it blocks muscarinic receptors in the vestibular system and the brainstem vomiting center. The side effects of drowsiness and dry mouth are due to its central and peripheral anticholinergic properties, respectively.
Question 11
A 52-year-old man who has smoked one pack of cigarettes per day for 30 years expresses a strong desire to quit. His physician prescribes varenicline. The physician explains that the drug will help reduce cravings and also make smoking less satisfying if he has a lapse.
Varenicline accomplishes these dual effects by acting as which of the following at central nicotinic acetylcholine receptors?
- Competitive antagonist
- Full agonist
- Partial agonist (correct answer)
- Non-competitive antagonist
Explanation: Varenicline is a partial agonist at the α4β2 nicotinic acetylcholine receptor subtype. As a partial agonist, it provides a moderate, sustained level of dopamine release in the mesolimbic pathway, which helps to reduce cravings and withdrawal symptoms (agonist activity). At the same time, it occupies the receptor and prevents nicotine from binding, thereby blocking the rewarding effects of smoking (antagonist activity).
Question 12
A 65-year-old woman with overactive bladder was treated with oxybutynin but had to discontinue it due to intolerable dry mouth and constipation. Her physician switches her to mirabegron, which she tolerates well.
Unlike oxybutynin, mirabegron improves symptoms of overactive bladder through which of the following mechanisms?
- Antagonism of muscarinic M3 receptors on the detrusor muscle
- Stimulation of beta-3 adrenergic receptors on the detrusor muscle (correct answer)
- Blockade of alpha-1 adrenergic receptors in the bladder neck
- Inhibition of phosphodiesterase type 5 in bladder smooth muscle
Explanation: Mirabegron is a beta-3 adrenergic agonist. Stimulation of beta-3 receptors on the detrusor muscle leads to smooth muscle relaxation, which increases the bladder's capacity to store urine and reduces symptoms of urgency and frequency. This mechanism is distinct from antimuscarinic drugs like oxybutynin, which block M3 receptors to prevent involuntary bladder contractions. Because mirabegron does not affect muscarinic receptors, it avoids the typical anticholinergic side effects.
Question 13
A 68-year-old man undergoes a prostatectomy. On postoperative day 2, he develops abdominal distention and is unable to void, despite having a palpable, distended bladder. A bladder scan confirms a volume of 700 mL. The physician administers bethanechol. The patient is able to urinate shortly thereafter.
Which of the following best describes the mechanism of action of the administered drug?
- Direct stimulation of muscarinic receptors on the detrusor muscle (correct answer)
- Inhibition of acetylcholinesterase at the neuromuscular junction
- Antagonism of muscarinic receptors in the bladder trigone
- Direct stimulation of nicotinic receptors at the autonomic ganglia
Explanation: Bethanechol is a direct-acting cholinomimetic that selectively stimulates muscarinic receptors, particularly M3 receptors on the detrusor muscle of the bladder and on smooth muscle of the GI tract. This stimulation leads to detrusor muscle contraction and relaxation of the trigone and sphincter, promoting urination. It is used to treat non-obstructive urinary retention.
Question 14
A 70-year-old man with benign prostatic hyperplasia (BPH) complains of urinary hesitancy and a weak stream. His blood pressure is 125/80 mm Hg. His physician prescribes tamsulosin. The patient asks why he was given this specific drug instead of another one he heard about, prazosin.
Tamsulosin has a lower incidence of orthostatic hypotension compared to prazosin because of its relative selectivity for which receptor subtype, which is concentrated in the prostate and bladder neck?
- Alpha-1A (correct answer)
- Alpha-1B
- Alpha-1D
- Alpha-2A
Explanation: Alpha-1 receptors have subtypes. Alpha-1A receptors are predominantly found in the smooth muscle of the prostate and bladder neck, and their blockade by tamsulosin relaxes these tissues, improving urinary flow in BPH. Alpha-1B receptors are primarily found in vascular smooth muscle. Prazosin is non-selective for these subtypes and blocks both, leading to significant vasodilation and a risk of orthostatic hypotension. Tamsulosin's selectivity for Alpha-1A makes it uroselective with fewer vascular side effects.
Question 15
A 66-year-old man with a long history of smoking presents with an acute exacerbation of chronic obstructive pulmonary disease (COPD), characterized by increased dyspnea and wheezing. He is treated in the emergency department with supplemental oxygen, systemic corticosteroids, and a nebulized solution containing albuterol and ipratropium.
What is the primary mechanism by which ipratropium provides therapeutic benefit in this patient?
- Stimulation of beta-2 adrenergic receptors, leading to bronchodilation
- Antagonism of muscarinic receptors, leading to bronchodilation (correct answer)
- Inhibition of phosphodiesterase, increasing intracellular cAMP
- Blockade of histamine H1 receptors on bronchial smooth muscle
Explanation: Ipratropium is a short-acting muscarinic antagonist (SAMA). It competitively blocks muscarinic receptors (primarily M3) on airway smooth muscle, preventing acetylcholine-induced bronchoconstriction. This results in bronchodilation. It is a quaternary amine, so it does not readily cross the blood-brain barrier and has minimal systemic side effects.
Question 16
A 58-year-old man with a history of moderate persistent asthma and a recent myocardial infarction is being evaluated for long-term medical therapy. His cardiologist considers prescribing propranolol.
The use of propranolol is relatively contraindicated in this patient due to its potential to cause which of the following?
- Hypertensive crisis
- Bronchoconstriction (correct answer)
- Diuresis
- Coronary vasospasm
Explanation: Propranolol is a non-selective beta-blocker, meaning it antagonizes both beta-1 and beta-2 adrenergic receptors. While the beta-1 blockade is beneficial for the heart post-MI, the blockade of beta-2 receptors in the lungs is problematic. Beta-2 receptors mediate bronchodilation. Blocking them can lead to bronchoconstriction, which can precipitate a severe asthma attack in susceptible individuals. Cardioselective beta-1 blockers (e.g., metoprolol, atenolol) are preferred in such patients.
Question 17
A 15-year-old boy is stung by a bee and rapidly develops diffuse urticaria, wheezing, and lightheadedness. In the emergency department, his blood pressure is 75/40 mm Hg and his heart rate is 130/min. He is given an intramuscular injection of epinephrine.
Which of the following effects of epinephrine is most critical for reversing this patient's life-threatening hypotension?
- Beta-1 receptor-mediated increase in cardiac contractility
- Beta-2 receptor-mediated bronchodilation
- Alpha-1 receptor-mediated vasoconstriction (correct answer)
- Beta-2 receptor-mediated inhibition of mast cell degranulation
Explanation: In anaphylactic shock, massive histamine release causes widespread vasodilation and capillary leak, leading to profound hypotension. Epinephrine is the treatment of choice because it addresses all aspects of anaphylaxis. However, the most critical life-saving effect for reversing shock is its potent alpha-1 agonist activity, which causes vasoconstriction, increases systemic vascular resistance, and raises blood pressure. The beta-2 effects (bronchodilation) and beta-1 effects (increased cardiac output) are also crucial but secondary to vasoconstriction for treating the shock itself.
Question 18
A 72-year-old woman presents to the emergency department with severe, deep right eye pain, headache, nausea, and blurred vision. On examination, her right pupil is fixed and mid-dilated, and the cornea appears hazy. Intraocular pressure is measured at 55 mm Hg (normal < 21 mm Hg). A diagnosis of acute angle-closure glaucoma is made. In addition to other therapies, pilocarpine eye drops are administered.
How does pilocarpine help to lower intraocular pressure in this condition?
- Decreasing the production of aqueous humor by the ciliary body
- Contracting the ciliary muscle, which opens the trabecular meshwork (correct answer)
- Relaxing the pupillary sphincter muscle, causing mydriasis
- Blocking beta-adrenergic receptors on the ciliary epithelium
Explanation: Pilocarpine is a direct-acting muscarinic agonist. In the eye, it causes contraction of the ciliary muscle (a parasympathetic action). This contraction pulls on the trabecular meshwork, increasing the outflow of aqueous humor and thereby lowering intraocular pressure. It also causes miosis (pupillary constriction), which can further help open the angle in angle-closure glaucoma.
Question 19
A 40-year-old woman with a confirmed diagnosis of myasthenia gravis is managed with long-term oral pyridostigmine. She reports a significant improvement in her symptoms of ptosis and generalized weakness with the medication.
Which of the following best describes the mechanism by which pyridostigmine improves muscle strength in this patient?
- It sensitizes postsynaptic nicotinic receptors to acetylcholine.
- It increases the presynaptic release of acetylcholine vesicles.
- It increases the duration of acetylcholine in the synaptic cleft. (correct answer)
- It acts as a direct agonist at the nicotinic receptor.
Explanation: Pyridostigmine is a long-acting, reversible acetylcholinesterase (AChE) inhibitor. By inhibiting the AChE enzyme, it prevents the breakdown of acetylcholine in the neuromuscular junction. This increases the concentration and prolongs the half-life of acetylcholine in the synaptic cleft, allowing it to better compete for the reduced number of functional nicotinic receptors characteristic of myasthenia gravis, thereby improving neuromuscular transmission and muscle strength.
Question 20
A 34-year-old woman with myasthenia gravis presents with increasing ptosis and diplopia that worsens throughout the day. She is treated with a medication that improves her muscle strength by increasing the amount of acetylcholine available at the neuromuscular junction. However, she also experiences abdominal cramps and diarrhea.
Which of the following is the most likely mechanism of the drug used to treat her muscle weakness?
- Directly agonizes postsynaptic nicotinic receptors
- Reversibly inhibits acetylcholinesterase (correct answer)
- Blocks presynaptic voltage-gated calcium channels
- Promotes the synthesis of acetylcholine in the presynaptic terminal
Explanation: Myasthenia gravis is treated with acetylcholinesterase (AChE) inhibitors, such as pyridostigmine or neostigmine. These drugs reversibly inhibit AChE, the enzyme that degrades acetylcholine in the synaptic cleft. This action increases the concentration and duration of action of acetylcholine at the neuromuscular junction, improving muscle strength. The side effects (cramps, diarrhea) are due to increased muscarinic stimulation in the GI tract.