A 23-year-old woman is brought to the emergency department 30 minutes after being found unresponsive on the floor by her boyfriend. Paramedics found several empty pill bottles next to her on the floor. According to her boyfriend, she has a history of insomnia and generalized anxiety disorder and was recently diagnosed with depression. Her temperature is 36°C (96.8°F), pulse is 64/min, respirations are 10/min and shallow, and blood pressure is 112/75 mm Hg. On examination, she does not open her eyes, makes incomprehensible sounds, and extends her extremities when a painful stimulus is applied. Her pupils are 3 mm and reactive to light. The corneal reflex is normal and gag reflex is absent. There is diffuse hypotonia and decreased deep tendon reflexes. Cardiopulmonary examination shows no abnormalities. She is intubated for airway protection. Mechanical ventilation and an infusion of 0.9% saline are begun. Which of the following would most likely reverse this patient's condition?
Q92
A 27-year-old woman presents to the emergency department because of muscle tightness and pain. She says that she has experienced increasing tightness and cramping of the muscles on the left side of her neck. She also says that she has trouble looking downwards because her “eyes are stuck.” She has a history of schizophrenia, which is being treated with haloperidol. Her temperature is 37.0°C (98.6°F), the pulse is 110/min, the respirations are 18/min, and the blood pressure is 115/71 mm Hg. Physical examination shows significant stiffness in her neck with muscle spasms. Her head is tilted severely to the left side, and her eyes are steady in upward gaze. Respiratory examination shows good air entry bilaterally with no wheezing. Which of the following medicines is the most appropriate next step in management?
Q93
A 60-year-old man presents to the emergency department complaining of worsening exertional dyspnea over the last week. He denies chest pain and lightheadedness but reports persistent cough with white sputum. His past medical history includes hypertension and diabetes mellitus. He has a 50 pack-year history of smoking but denies any illicit drug use or alcohol consumption. His temperature is 101°F (38.3°C), blood pressure is 154/104 mmHg, pulse is 110/min, respirations are 26/min, and oxygen saturation is 88% on a non-rebreather mask. Physical exam is notable for an obese man in distress. The anteroposterior diameter of the patient's chest is increased, and he has decreased breath sounds bilaterally with diffuse expiratory wheezing. Which of the following is the best next step in management?
Q94
A 50-year-old man comes to the physician because of gradually worsening rhythmic movements of his right hand for the past 5 months. His symptoms worsen when he is in a meeting and he is concerned that people are noticing it more frequently. There is no personal or family history of serious illness, but the patient recalls that his father developed bobbing of the head in older age. He takes no medications. Neurological examination shows a tremor of the right hand when the limbs are relaxed. When the patient is asked to move his arm the tremor decreases. He has reduced arm swing while walking. Which of the following is the most appropriate pharmacotherapy?
Q95
A 77-year-old man with refractory shock has been under treatment in an intensive care unit for last 7 days. Despite the best possible management by the team of physicians and intensivists, he fails to show improvement. After discussion with his relatives and obtaining informed consent from them, the team administers to him a novel drug, an adrenergic agonist that produces positive chronotropic effects and inotropic effects and stimulates the release of renin from the kidneys. The drug does not have any other adrenergic effects. Which of the following second messengers is most likely to be responsible for the actions of the novel drug?
Q96
A 43-year-old woman presents for a routine checkup. She says she has been uncontrollably grimacing and smacking her lips for the past 2 months, and these symptoms have been getting progressively worse. Past medical history is significant for schizophrenia, managed medically with haloperidol. Which of the following is the most likely diagnosis in this patient?
Q97
A 46-year-old man presents to the emergency department with confusion, lacrimation, salivation, nausea, vomiting, abdominal pain, and diarrhea. He developed these symptoms 30 minutes after he finished treating his garden with the insecticide malathion. His vital signs are as follows: blood pressure is 85/50 mm Hg, heart rate is 49/min, respiratory rate is 12/min, and temperature is 36.5℃ (97.7℉). At presentation, the patient is lethargic. Physical examination reveals pallor, miosis, nystagmus, widespread bilateral loud wheezes on lung auscultation, decreased heart sounds on cardiac auscultation, abdominal tenderness, and bilaterally increased upper and lower extremities muscle tone. Which of the following statements is true?
Q98
A 7-year-old boy is brought in to clinic by his parents with a chief concern of poor performance in school. The parents were told by the teacher that the student often does not turn in assignments, and when he does they are partially complete. The child also often shouts out answers to questions and has trouble participating in class sports as he does not follow the rules. The parents of this child also note similar behaviors at home and have trouble getting their child to focus on any task such as reading. The child is even unable to watch full episodes of his favorite television show without getting distracted by other activities. The child begins a trial of behavioral therapy that fails. The physician then tries pharmacological therapy. Which of the following is most likely the mechanism of action of an appropriate treatment for this child's condition?
Q99
A 52-year-old man presents to his primary care physician for a yearly checkup complaining of recent weight gain. The patient states that he has noticed that, regardless of his diet, his midsection has gotten increasingly larger and his old clothes no longer fit. The patient has a 2-year history of left hip arthritis from a car accident for which he is on prednisone, as well as a history of migraine headaches. The patient has also noticed that in the last 2 months, he has developed acne and his face has become fuller in appearance. On exam, the patient has gained 26 pounds since his previous checkup 1 year prior, and he now has a BMI 28.2 kg/m^2 (up from 24.1 kg/m^2 previously). His temperature is 98.3°F (36.8°C), blood pressure is 134/94 mmHg, pulse is 72/min, and respirations are 12/min. His physical exam is notable for red striae on his shoulders and around his waist. On his labs, the patient’s serum ACTH is found to be decreased. Which of the following changes is most likely expected?
Q100
A 40-year-old man is brought to an urgent care clinic by his wife with complaints of dizziness and blurring of vision for several hours. His wife adds that he has had slurred speech since this morning and complained of difficulty swallowing last night. His wife mentions that her husband was working outdoors and ate stew with roasted beef and potatoes that had been sitting on the stove for the past 3 days. The patient's past medical history is unremarkable. A physical examination reveals right eye ptosis and palatal weakness with an impaired gag reflex. Cranial nerve examination reveals findings suggestive of multiple cranial nerve involvement. What is the mechanism of action of the toxin that is the most likely cause of this patient's symptoms?
Cholinergic/Adrenergic drugs US Medical PG Practice Questions and MCQs
Question 91: A 23-year-old woman is brought to the emergency department 30 minutes after being found unresponsive on the floor by her boyfriend. Paramedics found several empty pill bottles next to her on the floor. According to her boyfriend, she has a history of insomnia and generalized anxiety disorder and was recently diagnosed with depression. Her temperature is 36°C (96.8°F), pulse is 64/min, respirations are 10/min and shallow, and blood pressure is 112/75 mm Hg. On examination, she does not open her eyes, makes incomprehensible sounds, and extends her extremities when a painful stimulus is applied. Her pupils are 3 mm and reactive to light. The corneal reflex is normal and gag reflex is absent. There is diffuse hypotonia and decreased deep tendon reflexes. Cardiopulmonary examination shows no abnormalities. She is intubated for airway protection. Mechanical ventilation and an infusion of 0.9% saline are begun. Which of the following would most likely reverse this patient's condition?
A. Sodium bicarbonate
B. Fomepizole
C. Flumazenil (Correct Answer)
D. Dextrose
E. Naloxone
Explanation: ***Flumazenil***
- This patient presents with **central nervous system (CNS) depression** (unresponsiveness, shallow respirations, hypotonia, absent gag reflex) following suspected pill overdose, consistent with **benzodiazepine toxicity**.
- **Flumazenil** is a competitive antagonist at the **GABA-A receptor**, effectively reversing the CNS depressant effects of benzodiazepines.
*Sodium bicarbonate*
- This is used to treat **tricyclic antidepressant (TCA) overdose**, which can cause widened QRS complexes and arrhythmias.
- The patient's presentation does not suggest TCA toxicity; specifically, she does not have **cardiac conduction abnormalities**.
*Fomepizole*
- This is an antidote for **methanol** or **ethylene glycol poisoning**, which causes severe metabolic acidosis and can lead to organ damage.
- There is no evidence of these specific intoxicants or their characteristic metabolic derangements in this patient.
*Dextrose*
- This is administered for **hypoglycemia**, which can cause altered mental status and unresponsiveness.
- While it's a common initial intervention in altered mental status, the patient's symptoms are more indicative of a drug overdose, and there's no specific indication of **low blood glucose**.
*Naloxone*
- This opioid antagonist is used to reverse **opioid overdose**, which typically presents with **miosis (pinpoint pupils)**, respiratory depression, and CNS depression.
- This patient has **3 mm reactive pupils**, making opioid overdose less likely as the primary cause of her symptoms.
Question 92: A 27-year-old woman presents to the emergency department because of muscle tightness and pain. She says that she has experienced increasing tightness and cramping of the muscles on the left side of her neck. She also says that she has trouble looking downwards because her “eyes are stuck.” She has a history of schizophrenia, which is being treated with haloperidol. Her temperature is 37.0°C (98.6°F), the pulse is 110/min, the respirations are 18/min, and the blood pressure is 115/71 mm Hg. Physical examination shows significant stiffness in her neck with muscle spasms. Her head is tilted severely to the left side, and her eyes are steady in upward gaze. Respiratory examination shows good air entry bilaterally with no wheezing. Which of the following medicines is the most appropriate next step in management?
A. Benztropine (Correct Answer)
B. Haloperidol
C. Lorazepam
D. Propranolol
E. Dantrolene
Explanation: ***Benztropine***
- This patient is experiencing an **acute dystonic reaction** caused by **haloperidol**, a dopamine receptor antagonist, and **benztropine** is an anticholinergic medication that effectively treats these reactions.
- **Acute dystonia** presents with sustained painful muscle contractions, often affecting the neck (torticollis), eyes (oculogyric crisis), or trunk.
*Haloperidol*
- Administering more haloperidol would **worsen** the patient's acute dystonia, as it is the causative agent.
- It works by blocking **dopamine D2 receptors**, leading to an imbalance with acetylcholine, which is what causes the dystonia.
*Lorazepam*
- While lorazepam (a benzodiazepine) can provide some symptomatic relief by **muscle relaxation**, it is not the primary treatment for acute dystonia.
- It would not address the underlying cholinergic-dopaminergic imbalance that causes the dystonia.
*Propranolol*
- Propranolol is a **beta-blocker** primarily used to treat akathisia (restlessness) or tremor side effects of antipsychotics, not acute dystonia.
- It would not be effective in resolving the severe muscle spasms and contractions seen in dystonia.
*Dantrolene*
- Dantrolene is a **muscle relaxant** often used to treat muscle rigidity and hyperthermia in conditions like **neuroleptic malignant syndrome (NMS)**.
- The patient's presentation does not include features of NMS (e.g., fever, autonomic instability), making dantrolene inappropriate for acute dystonia.
Question 93: A 60-year-old man presents to the emergency department complaining of worsening exertional dyspnea over the last week. He denies chest pain and lightheadedness but reports persistent cough with white sputum. His past medical history includes hypertension and diabetes mellitus. He has a 50 pack-year history of smoking but denies any illicit drug use or alcohol consumption. His temperature is 101°F (38.3°C), blood pressure is 154/104 mmHg, pulse is 110/min, respirations are 26/min, and oxygen saturation is 88% on a non-rebreather mask. Physical exam is notable for an obese man in distress. The anteroposterior diameter of the patient's chest is increased, and he has decreased breath sounds bilaterally with diffuse expiratory wheezing. Which of the following is the best next step in management?
A. Muscarinic blocker
B. Glucocorticoid-analog
C. Alpha-2 blocker
D. Beta-2 agonist (Correct Answer)
E. Alpha-1 blocker
Explanation: ***Beta-2 agonist***
- The patient presents with **acute exacerbation of COPD**, evidenced by his significant smoking history (50 pack-years), barrel chest (increased AP diameter), decreased breath sounds, and diffuse expiratory wheezing.
- **Short-acting beta-2 agonists (SABAs)** like **albuterol** are **first-line bronchodilators** in acute COPD exacerbations, providing rapid relief of bronchospasm by relaxing airway smooth muscle.
- According to **GOLD guidelines**, SABAs are the primary initial bronchodilator, often combined with short-acting muscarinic antagonists (SAMAs) like ipratropium for optimal effect.
- This patient requires **immediate bronchodilation** to address severe dyspnea and hypoxemia (88% on non-rebreather).
*Muscarinic blocker*
- **Short-acting muscarinic antagonists (SAMAs)** like **ipratropium bromide** are important adjunctive bronchodilators in acute COPD exacerbations.
- While SAMAs are effective and typically used **in combination with SABAs**, they are generally considered **adjunctive rather than first-line monotherapy**.
- In clinical practice, both SABAs and SAMAs are often administered together, but when asked for the "best next step," **beta-2 agonist is the more standard initial choice**.
*Glucocorticoid-analog*
- Systemic **glucocorticoids** like **prednisone** are indeed crucial in managing acute COPD exacerbations to reduce airway inflammation and shorten recovery time.
- However, they do **not provide immediate bronchodilation**, which is the most urgent need for this patient with severe respiratory distress and hypoxemia.
- Glucocorticoids are typically administered **after or concurrent with bronchodilators**, not as the initial intervention.
*Alpha-2 blocker*
- **Alpha-2 blockers have no role** in the management of acute respiratory distress or COPD exacerbations.
- These agents are used for conditions like **hypertension** or psychiatric disorders (note: clonidine is actually an alpha-2 **agonist**, not blocker).
- They do not affect airway caliber and are completely unrelated to bronchodilation.
*Alpha-1 blocker*
- **Alpha-1 blockers** like prazosin or doxazosin are used for **hypertension or benign prostatic hyperplasia (BPH)**.
- They have **no role in acute respiratory management** or COPD exacerbations.
- These agents cause peripheral vasodilation and do not affect airway smooth muscle or bronchospasm.
Question 94: A 50-year-old man comes to the physician because of gradually worsening rhythmic movements of his right hand for the past 5 months. His symptoms worsen when he is in a meeting and he is concerned that people are noticing it more frequently. There is no personal or family history of serious illness, but the patient recalls that his father developed bobbing of the head in older age. He takes no medications. Neurological examination shows a tremor of the right hand when the limbs are relaxed. When the patient is asked to move his arm the tremor decreases. He has reduced arm swing while walking. Which of the following is the most appropriate pharmacotherapy?
A. Trihexyphenidyl
B. Propranolol
C. Clonazepam
D. Donepezil
E. Levodopa/carbidopa (Correct Answer)
Explanation: ***Levodopa/carbidopa***
- The patient's symptoms (gradually worsening rhythmic movements, **resting tremor** which improves with action, reduced arm swing, and possible family history of head bobbing/tremor) are highly suggestive of **Parkinson's disease**.
- **Levodopa/carbidopa** is the most effective medication for symptomatic treatment of Parkinson's disease, particularly for motor symptoms like tremor, bradykinesia, and rigidity.
*Trihexyphenidyl*
- This is an **anticholinergic** medication that can be used to treat tremor in Parkinson's disease, but it is generally less effective than levodopa and has more side effects, especially in older patients (e.g., confusion, dry mouth, blurred vision).
- It is typically considered for younger patients with prominent tremor rather than older individuals or those with a broader range of motor symptoms.
*Propranolol*
- **Propranolol** is a beta-blocker primarily used to treat **essential tremor**, a condition characterized by an action or postural tremor that improves with alcohol and often has a strong family history.
- The patient's tremor is a **resting tremor** that decreases with action, making essential tremor less likely.
*Clonazepam*
- **Clonazepam** is a benzodiazepine that is used to treat various conditions, including anxiety, seizures, and some movement disorders (e.g., restless legs syndrome, clonus).
- It is not a primary treatment for Parkinson's disease tremor and would not address the other motor symptoms like reduced arm swing.
*Donepezil*
- **Donepezil** is an **acetylcholinesterase inhibitor** used to treat the cognitive symptoms of Alzheimer's disease and other dementias.
- It has no role in the treatment of the motor symptoms of Parkinson's disease.
Question 95: A 77-year-old man with refractory shock has been under treatment in an intensive care unit for last 7 days. Despite the best possible management by the team of physicians and intensivists, he fails to show improvement. After discussion with his relatives and obtaining informed consent from them, the team administers to him a novel drug, an adrenergic agonist that produces positive chronotropic effects and inotropic effects and stimulates the release of renin from the kidneys. The drug does not have any other adrenergic effects. Which of the following second messengers is most likely to be responsible for the actions of the novel drug?
A. Calcium ion
B. Cyclic adenosine monophosphate (cAMP) (Correct Answer)
C. Cyclic guanosine monophosphate (cGMP)
D. Diacylglycerol (DAG)
E. Inositol 1,4,5-triphosphate (IP3)
Explanation: **Cyclic adenosine monophosphate (cAMP)**
- The drug described is an **adrenergic agonist** with **positive chronotropic** and **inotropic effects**, and it stimulates **renin release**. These actions are characteristic of **beta-1 (β1) adrenergic receptor** activation.
- Activation of β1 receptors is coupled to **G protein-coupled receptors (GPCRs)** that activate **adenylyl cyclase**, leading to an increase in intracellular **cAMP**, which acts as the second messenger.
*Calcium ion*
- While **calcium ions** are crucial for cardiac contractility and renin release, they are often directly modulated downstream by events initiated by second messengers like **cAMP** or **IP3/DAG**, rather than being the primary direct second messenger for β1-adrenergic stimulation.
- For example, increased cAMP in cardiac cells leads to **phosphorylation of L-type calcium channels**, increasing calcium influx, but cAMP itself is the direct initiating second messenger.
*Cyclic guanosine monophosphate (cGMP)*
- **cGMP** is typically associated with pathways activated by **nitric oxide** and **natriuretic peptides**, leading to vasodilation and smooth muscle relaxation, which are not the primary effects described for this drug.
- Drugs that activate **guanylyl cyclase** to increase cGMP would generally have opposite effects to the cardiotonic and renin-releasing actions mentioned.
*Diacylglycerol (DAG)*
- **DAG** is a second messenger produced along with **IP3** by the activation of **phospholipase C**, typically initiated by **alpha-1 (α1) adrenergic receptors** or other Gq-coupled GPCRs.
- α1 adrenergic activation causes **vasoconstriction** and other effects, which are distinct from the positive chronotropic and inotropic actions of a β1 agonist.
*Inositol 1,4,5-triphosphate (IP3)*
- **IP3** is generated alongside **DAG** through the activation of **phospholipase C**, following the binding of agonists to **Gq-coupled receptors** like the α1 adrenergic receptor.
- Its primary role is to trigger the release of **calcium from intracellular stores**, which, while important for muscle contraction, is not the direct second messenger pathway for the described β1-adrenergic actions.
Question 96: A 43-year-old woman presents for a routine checkup. She says she has been uncontrollably grimacing and smacking her lips for the past 2 months, and these symptoms have been getting progressively worse. Past medical history is significant for schizophrenia, managed medically with haloperidol. Which of the following is the most likely diagnosis in this patient?
A. Oculogyric crisis
B. Trismus
C. Tourette’s syndrome
D. Torticollis
E. Tardive dyskinesia (Correct Answer)
Explanation: ***Tardive dyskinesia***
- The symptoms of **uncontrollable grimacing** and **lip smacking** are classic presentations of **tardive dyskinesia**, an involuntary movement disorder.
- This condition often develops after **chronic use of dopamine receptor-blocking agents**, such as typical antipsychotics like **haloperidol**.
- Tardive dyskinesia typically emerges after months to years of antipsychotic therapy and is more commonly associated with first-generation (typical) antipsychotics.
*Oculogyric crisis*
- This is a form of **acute dystonia** characterized by **sustained upward deviation of the eyes**.
- While it can be induced by antipsychotics, the present symptoms of grimacing and lip smacking are not characteristic of an oculogyric crisis.
*Trismus*
- Trismus refers to a **limited range of motion of the jaw** or a **sustained contraction of the jaw muscles**.
- This condition primarily affects the jaw and would not explain the grimacing or lip-smacking movements.
*Tourette's syndrome*
- Tourette's syndrome is characterized by **multiple motor tics** and at least one **vocal tic** that persist for more than a year.
- While some tics can involve facial movements, the sudden onset in adulthood after medication use points away from Tourette's, which typically presents in childhood.
*Torticollis*
- Torticollis, or **wry neck**, is a focal dystonia characterized by a sustained or intermittent **contraction of neck muscles**, leading to abnormal head posture.
- This condition primarily affects the neck and head posture and does not explain the oral-facial dyskinesias described.
Question 97: A 46-year-old man presents to the emergency department with confusion, lacrimation, salivation, nausea, vomiting, abdominal pain, and diarrhea. He developed these symptoms 30 minutes after he finished treating his garden with the insecticide malathion. His vital signs are as follows: blood pressure is 85/50 mm Hg, heart rate is 49/min, respiratory rate is 12/min, and temperature is 36.5℃ (97.7℉). At presentation, the patient is lethargic. Physical examination reveals pallor, miosis, nystagmus, widespread bilateral loud wheezes on lung auscultation, decreased heart sounds on cardiac auscultation, abdominal tenderness, and bilaterally increased upper and lower extremities muscle tone. Which of the following statements is true?
A. Malathion activates the enzyme responsible for acetylcholine breakdown by modifying its allosteric site.
B. Maximum reaction rate (Vmax) of the affected enzyme is not changed in this patient.
C. The patient’s symptoms are caused by reversible enzyme inhibition.
D. The affected enzyme is inhibited by malathion via the formation of hydrogen bonds between its allosteric site and malathion phosphoric groups.
E. The patient’s symptoms result from the formation of covalent bonds between malathion and the affected enzyme. (Correct Answer)
Explanation: ***The patient’s symptoms result from the formation of covalent bonds between malathion and the affected enzyme.***
- Malathion is an **organophosphate insecticide** that irreversibly inhibits **acetylcholinesterase** by forming a stable **covalent bond** with a serine residue in the enzyme's active site.
- This **covalent modification** prevents the enzyme from breaking down acetylcholine, leading to its accumulation and **cholinergic crisis**, which explains the patient's symptoms (confusion, lacrimation, salivation, bradycardia, wheezing, GI symptoms).
*Malathion activates the enzyme responsible for acetylcholine breakdown by modifying its allosteric site.*
- Malathion **inhibits**, not activates, the enzyme **acetylcholinesterase**, which is responsible for acetylcholine breakdown.
- The inhibition occurs at the **active site**, not the allosteric site, via **covalent bonding**, not allosteric modification.
*Maximum reaction rate (Vmax) of the affected enzyme is not changed in this patient.*
- Organophosphate poisoning causes **irreversible inhibition** of acetylcholinesterase, effectively reducing the amount of functional enzyme.
- This reduction in functional enzyme directly leads to a **decrease in the Vmax** of the reaction, as fewer enzyme active sites are available to process the substrate.
*The patient’s symptoms are caused by reversible enzyme inhibition.*
- Organophosphates like malathion are known for causing **irreversible inhibition** of acetylcholinesterase through the formation of a stable **covalent bond**, which requires the synthesis of new enzyme.
- **Reversible inhibition** can be overcome by increasing substrate concentration or removing the inhibitor, which is not the case here given the severity and persistence of symptoms.
*The affected enzyme is inhibited by malathion via the formation of hydrogen bonds between its allosteric site and malathion phosphoric groups.*
- Malathion inhibits the enzyme by forming a **covalent bond** at the **active site**, specifically with a serine residue, rather than through hydrogen bonds at an allosteric site.
- The **phosphoric groups** of malathion interact directly with the active site, leading to phosphorylation of the enzyme and its inactivation.
Question 98: A 7-year-old boy is brought in to clinic by his parents with a chief concern of poor performance in school. The parents were told by the teacher that the student often does not turn in assignments, and when he does they are partially complete. The child also often shouts out answers to questions and has trouble participating in class sports as he does not follow the rules. The parents of this child also note similar behaviors at home and have trouble getting their child to focus on any task such as reading. The child is even unable to watch full episodes of his favorite television show without getting distracted by other activities. The child begins a trial of behavioral therapy that fails. The physician then tries pharmacological therapy. Which of the following is most likely the mechanism of action of an appropriate treatment for this child's condition?
A. Increases the frequency of GABAa channel opening
B. Increases the duration of GABAa channel opening
C. Decreases synaptic reuptake of norepinephrine and dopamine (Correct Answer)
D. Blockade of D2 receptors
E. Antagonizes NMDA receptors
Explanation: ***Decreases synaptic reuptake of norepinephrine and dopamine***
- The presented symptoms (inattention, impulsivity, hyperactivity) are characteristic of **Attention-Deficit/Hyperactivity Disorder (ADHD)**.
- The most common pharmacological treatments for ADHD are **stimulants** (e.g., methylphenidate, amphetamines) which work by **inhibiting the reuptake of norepinephrine and dopamine**, thereby increasing their synaptic concentrations.
*Increases the frequency of GABAa channel opening*
- This is the mechanism of action for **benzodiazepines**, which are primarily used for anxiety, seizures, and insomnia.
- Benzodiazepines are not indicated for ADHD and would likely worsen symptoms due to their sedative effects.
*Increases the duration of GABAa channel opening*
- This describes the mechanism of action of **barbiturates**, which are potent central nervous system depressants.
- Like benzodiazepines, barbiturates are not used for ADHD and would have inappropriate sedative side effects.
*Blockade of D2 receptors*
- This is the primary mechanism of action for **antipsychotic medications**, used to treat conditions like schizophrenia or bipolar disorder.
- Blocking D2 receptors would likely cause side effects such as drowsiness and extrapyramidal symptoms, and would not address the core symptoms of ADHD.
*Antagonizes NMDA receptors*
- NMDA receptor antagonists (e.g., memantine, ketamine) are used in conditions like **Alzheimer's disease** or for anesthetic purposes.
- This mechanism is not relevant to the treatment of ADHD; enhancing NMDA receptor activity might actually be beneficial in some cognitive disorders.
Question 99: A 52-year-old man presents to his primary care physician for a yearly checkup complaining of recent weight gain. The patient states that he has noticed that, regardless of his diet, his midsection has gotten increasingly larger and his old clothes no longer fit. The patient has a 2-year history of left hip arthritis from a car accident for which he is on prednisone, as well as a history of migraine headaches. The patient has also noticed that in the last 2 months, he has developed acne and his face has become fuller in appearance. On exam, the patient has gained 26 pounds since his previous checkup 1 year prior, and he now has a BMI 28.2 kg/m^2 (up from 24.1 kg/m^2 previously). His temperature is 98.3°F (36.8°C), blood pressure is 134/94 mmHg, pulse is 72/min, and respirations are 12/min. His physical exam is notable for red striae on his shoulders and around his waist. On his labs, the patient’s serum ACTH is found to be decreased. Which of the following changes is most likely expected?
A. Bilateral adrenal hyperplasia
B. Lung malignancy
C. Unilateral adrenal atrophy
D. Bilateral adrenal atrophy (Correct Answer)
E. Unilateral adrenal hyperplasia
Explanation: **Bilateral adrenal atrophy**
- The patient's symptoms (weight gain, central obesity, red striae, acne, moon facies, hypertension) are consistent with **Cushing's syndrome**.
- Given the history of chronic prednisone use for arthritis and decreased ACTH, this points to **exogenous corticosteroid use** causing suppression of the hypothalamic-pituitary-adrenal (HPA) axis, resulting in bilateral adrenal atrophy.
*Bilateral adrenal hyperplasia*
- This would typically be seen in ACTH-dependent Cushing's syndrome, such as from a **pituitary adenoma** (Cushing's disease), where ACTH levels would be elevated or inappropriately normal, not decreased.
- Adrenal hyperplasia implies increased adrenal gland size and activity, which is contrary to the expected effect of chronic exogenous steroid use.
*Unilateral adrenal atrophy*
- Unilateral atrophy would be highly unusual in the context of chronic exogenous steroid use, which affects both adrenal glands equally through ACTH suppression.
- This might be seen if there was a **unilateral adrenal tumor** producing cortisol, leading to decreased ACTH and atrophy of the contralateral gland, but the provided ACTH level and clinical picture don't support this.
*Lung malignancy*
- While **small cell lung cancer** can cause Cushing's syndrome through ectopic ACTH production, this would present with **elevated ACTH** levels, contradicting the patient's decreased ACTH.
- The primary context here is chronic prednisone use, making ectopic ACTH less likely.
*Unilateral adrenal hyperplasia*
- This could occur with a **unilateral adrenal tumor** producing cortisol, leading to Cushing's syndrome and suppressed ACTH, but would cause atrophy of the *contralateral* adrenal gland, not unilateral hyperplasia alone.
- The patient's history of chronic prednisone use is the key factor, leading to bilateral suppression and atrophy.
Question 100: A 40-year-old man is brought to an urgent care clinic by his wife with complaints of dizziness and blurring of vision for several hours. His wife adds that he has had slurred speech since this morning and complained of difficulty swallowing last night. His wife mentions that her husband was working outdoors and ate stew with roasted beef and potatoes that had been sitting on the stove for the past 3 days. The patient's past medical history is unremarkable. A physical examination reveals right eye ptosis and palatal weakness with an impaired gag reflex. Cranial nerve examination reveals findings suggestive of multiple cranial nerve involvement. What is the mechanism of action of the toxin that is the most likely cause of this patient's symptoms?
A. Ribosylation of the Gs protein
B. Inhibition of glycine and GABA
C. Expression of superantigen
D. Inhibition of the release of acetylcholine (Correct Answer)
E. Ribosylation of eukaryotic elongation factor-2
Explanation: ***Inhibition of the release of acetylcholine***
- The patient's symptoms (dizziness, blurred vision, slurred speech, difficulty swallowing, ptosis, palatal weakness, impaired gag reflex, CN V and VII lesions) are consistent with **botulism**, caused by *Clostridium botulinum* toxin.
- **Botulinum toxin** acts by cleaving SNARE proteins (syntaxin, SNAP-25, and synaptobrevin) at the neuromuscular junction, thereby **inhibiting acetylcholine (ACh) release** from presynaptic terminals and causing flaccid paralysis.
*Ribosylation of the Gs protein*
- This mechanism is characteristic of **cholera toxin** and **heat-labile enterotoxin** of *E. coli*.
- It leads to persistent activation of adenylate cyclase, resulting in increased cyclic AMP and causing **secretory diarrhea**, which is not seen here.
*Inhibition of glycine and GABA*
- This mechanism is associated with **tetanus toxin**, produced by *Clostridium tetani*.
- Tetanus toxin acts by blocking the release of inhibitory neurotransmitters **glycine** and **GABA** in the spinal cord, leading to spastic paralysis and muscle rigidity.
*Expression of superantigen*
- **Superantigens** are toxins produced by bacteria like *Staphylococcus aureus* (e.g., toxic shock syndrome toxin-1) and *Streptococcus pyogenes*.
- They cause widespread activation of T cells, leading to a massive inflammatory response and symptoms like **fever, rash, and hypotension**, rather than neurological deficits.
*Ribosylation of eukaryotic elongation factor-2*
- This is the mechanism of action of **diphtheria toxin**, produced by *Corynebacterium diphtheriae*.
- It inhibits protein synthesis in eukaryotic cells, leading to **cell death** and symptoms like pharyngitis, pseudomembrane formation, and myocarditis, not the paralytic symptoms described.
