A 51-year-old woman presents to your office with 2 weeks of fatigue and generalized weakness. She has a past medical history of diabetes, hypertension, and hyperlipidemia. She was recently diagnosed with rheumatoid arthritis and started on disease-modifying therapy. She states she has felt less able to do things she enjoys and feels guilty she can't play sports with her children. Review of systems is notable for the patient occasionally seeing a small amount of bright red blood on the toilet paper. Laboratory studies are ordered as seen below.
Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 7,700/mm^3 with normal differential
Platelet count: 207,000/mm^3
MCV: 110 fL
Which of the following is the most likely etiology of this patient's fatigue?
Q232
A 67-year-old man presents to the emergency department with trouble urinating. The patient states that in general he has had difficulty urinating but recently, it has taken significant effort for him to initiate a urinary stream. He finds himself unable to completely void and states he has suprapubic tenderness as a result. These symptoms started suddenly 3 days ago. The patient has a history of benign prostatic hyperplasia, constipation, and diabetes mellitus. His current medications include finasteride, sodium docusate, and hydrochlorothiazide. He recently started taking phenylephrine for seasonal allergies. The patient’s last bowel movement was 2 days ago. His temperature is 99.0°F (37.2°C), blood pressure is 167/98 mmHg, pulse is 90/min, respirations are 14/min, and oxygen saturation is 100% on room air. Physical exam is notable for suprapubic tenderness, and an ultrasound reveals 750 mL of fluid in the bladder. Which of the following is the most likely etiology of this patient’s symptoms?
Q233
A 62-year-old woman is referred to a tertiary care hospital with a history of diplopia and fatigue for the past 3 months. She has also noticed difficulty in climbing the stairs and combing her hair. She confirms a history of 2.3 kg (5.0 lb) weight loss in the past 6 weeks and constipation. Past medical history is significant for type 2 diabetes mellitus. She has a 50-pack-year cigarette smoking history. Physical examination reveals a blood pressure of 135/78 mm Hg supine and 112/65 while standing, a heart rate of 82/min supine and 81/min while standing, and a temperature of 37.0°C (98.6°F). She is oriented to time and space. Her right upper eyelid is slightly drooped. She has difficulty in abducting the right eye. Pupils are bilaterally equal and reactive to light with accommodation. The corneal reflex is intact. Muscle strength is reduced in the proximal muscles of all 4 limbs, and the lower limbs are affected more when compared to the upper limbs. Deep tendon reflexes are bilaterally absent. After 10 minutes of cycling, the reflexes become positive. Sensory examination is normal. Diffuse wheezes are heard on chest auscultation. Which of the following findings is expected?
Q234
A 42-year-old woman comes to the physician because of progressive weakness. She has noticed increasing difficulty performing household chores and walking her dog over the past month. Sometimes she feels too fatigued to cook dinner. She has noticed that she feels better after sleeping. She does not have chest pain, shortness of breath, or a history of recent illness. She has no personal history of serious illness and takes no medications. She has smoked two packs of cigarettes daily for 25 years. She appears fatigued. Her temperature is 37°C (98.8°F), pulse is 88/min, and blood pressure is 148/80 mm Hg. Pulse oximetry shows an oxygen saturation of 98% in room air. Bilateral expiratory wheezes are heard at both lung bases. Examination shows drooping of the upper eyelids. There is diminished motor strength in her upper extremities. Her sensation and reflexes are intact. A treatment with which of the following mechanisms of action is most likely to be effective?
Q235
In an attempt to create other selective dopamine 1 (D1) agonists, a small pharmaceutical company created a cell-based chemical screen that involved three modified receptors - alpha 1 (A1), beta 1 (B1), and D1. In the presence of D1 stimulation, the cell would produce an mRNA that codes for a fluorescent protein; however, if the A1 or B1 receptors are also stimulated at the same time, the cells would degrade the mRNA of the fluorescent protein thereby preventing it from being produced. Which of the following would best serve as a positive control for this experiment?
Q236
A 48-year-old man is unable to pass urine after undergoing open abdominal surgery. His physical examination and imaging findings suggest that the cause of his urinary retention is non-obstructive and is most probably due to urinary bladder atony. He is prescribed a new selective muscarinic (M3) receptor agonist, which improves his symptoms. Which of the following is most likely involved in the mechanism of action of this new drug?
Q237
A 31-year-old woman is brought to the physician because of increasing restlessness over the past 2 weeks. She reports that she continuously paces around the house and is unable to sit still for more than 10 minutes at a time. During this period, she has had multiple episodes of anxiety with chest tightness and shortness of breath. She was diagnosed with a psychotic illness 2 months ago. Her current medications include haloperidol and a multivitamin. She appears agitated. Vital signs are within normal limits. Physical examination shows no abnormalities. The examination was interrupted multiple times when she became restless and began to walk around the room. To reduce the likelihood of the patient developing her current symptoms, a drug with which of the following mechanisms of action should have been prescribed instead of her current medication?
Q238
A 23-year-old man presents to the emergency department with shortness of breath. The patient was at a lunch hosted by his employer. He started to feel his symptoms begin when he started playing football outside with a few of the other employees. The patient has a past medical history of atopic dermatitis and asthma. His temperature is 98.3°F (36.8°C), blood pressure is 87/58 mmHg, pulse is 150/min, respirations are 22/min, and oxygen saturation is 85% on room air. Which of the following is the best next step in management?
Q239
A 65-year-old patient with a history of COPD and open-angle glaucoma in the left eye has had uncontrolled intraocular pressure (IOP) for the last few months. She is currently using latanoprost eye drops. Her ophthalmologist adds another eye drop to her regimen to further decrease her IOP. A week later, the patient returns because of persistent dim vision. On exam, she has a small fixed pupil in her left eye as well as a visual acuity of 20/40 in her left eye compared to 20/20 in her right eye. Which of the following is the mechanism of action of the medication most likely prescribed in this case?
Q240
A 5-year-old boy is brought to the emergency department by his parents for difficulty breathing. He was playing outside in the snow and had progressive onset of wheezing and gasping. His history is notable for eczema and nut allergies. The patient has respirations of 22/min and is leaning forward with his hands on his legs as he is seated on the table. Physical examination is notable for inspiratory and expiratory wheezes on exam. A nebulized medication is started and begins to relieve his breathing difficulties. Which of the following is increased in this patient as a result of this medication?
Cholinergic/Adrenergic drugs US Medical PG Practice Questions and MCQs
Question 231: A 51-year-old woman presents to your office with 2 weeks of fatigue and generalized weakness. She has a past medical history of diabetes, hypertension, and hyperlipidemia. She was recently diagnosed with rheumatoid arthritis and started on disease-modifying therapy. She states she has felt less able to do things she enjoys and feels guilty she can't play sports with her children. Review of systems is notable for the patient occasionally seeing a small amount of bright red blood on the toilet paper. Laboratory studies are ordered as seen below.
Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 7,700/mm^3 with normal differential
Platelet count: 207,000/mm^3
MCV: 110 fL
Which of the following is the most likely etiology of this patient's fatigue?
A. Depression
B. Gastrointestinal bleed
C. Iron deficiency
D. Medication side effect
E. Vitamin B12 deficiency (Correct Answer)
Explanation: ***Vitamin B12 deficiency***
- The elevated **MCV (110 fL)** indicates **macrocytic anemia**, which is often caused by a vitamin B12 deficiency, leading to fatigue and weakness.
- While other causes of fatigue are present, the specific lab finding of macrocytosis points directly to vitamin B12 deficiency as the most likely cause of her current symptoms.
*Depression*
- While feelings of guilt, loss of enjoyment, and fatigue could be symptoms of **depression**, the clear **macrocytic anemia** in the lab results points to a distinct physical cause.
- Depression is a common comorbidity, especially with chronic diseases like rheumatoid arthritis, but is less likely to be the primary cause of fatigue in the presence of such a dominant lab finding.
*Gastrointestinal bleed*
- Bright red blood on toilet paper suggests a **lower GI bleed** (e.g., hemorrhoids), but this type of bleed typically leads to **iron deficiency anemia** with a **microcytic MCV** (low MCV), not high MCV.
- The patient's hemoglobin and hematocrit are not severely low, making an acute significant bleed less likely to be the sole cause of her profound fatigue and macrocytic anemia.
*Iron deficiency*
- **Iron deficiency** usually presents with **microcytic anemia** (low MCV), typically less than 80 fL, and often results from chronic blood loss, such as in this patient's reported rectal bleeding.
- The presented elevated **MCV of 110 fL** directly contradicts iron deficiency as the primary cause of her fatigue and anemia.
*Medication side effect*
- While many medications can cause fatigue, there's no specific information provided about new medications that commonly lead to **macrocytic anemia** (e.g., methotrexate without folate supplementation).
- Without details on her specific disease-modifying therapy for rheumatoid arthritis and in the presence of a clear finding for macrocytic anemia, medication side effect is a less direct explanation.
Question 232: A 67-year-old man presents to the emergency department with trouble urinating. The patient states that in general he has had difficulty urinating but recently, it has taken significant effort for him to initiate a urinary stream. He finds himself unable to completely void and states he has suprapubic tenderness as a result. These symptoms started suddenly 3 days ago. The patient has a history of benign prostatic hyperplasia, constipation, and diabetes mellitus. His current medications include finasteride, sodium docusate, and hydrochlorothiazide. He recently started taking phenylephrine for seasonal allergies. The patient’s last bowel movement was 2 days ago. His temperature is 99.0°F (37.2°C), blood pressure is 167/98 mmHg, pulse is 90/min, respirations are 14/min, and oxygen saturation is 100% on room air. Physical exam is notable for suprapubic tenderness, and an ultrasound reveals 750 mL of fluid in the bladder. Which of the following is the most likely etiology of this patient’s symptoms?
A. Prostatic adenocarcinoma
B. Medication-induced symptoms (Correct Answer)
C. Constipation
D. Urinary tract infection
E. Worsening benign prostatic hypertrophy
Explanation: ***Medication-induced symptoms***
- The patient recently started **phenylephrine**, an **alpha-1 adrenergic agonist**, which can cause **urethral constriction** and worsen urinary outflow obstruction, especially in patients with BPH.
- The **sudden onset** of severe urinary retention, leading to suprapubic tenderness and a distended bladder (750 mL), is highly suggestive of a medication side effect given his existing BPH.
*Prostatic adenocarcinoma*
- While prostatic adenocarcinoma can cause urinary symptoms, these typically develop **gradually** and are less likely to present with such an acute, severe urinary retention episode.
- There are no other features like **weight loss**, **bone pain**, or abnormal **PSA levels** mentioned to suggest malignancy.
*Constipation*
- Although **severe constipation** can sometimes exacerbate urinary symptoms by physical compression on the bladder, the patient's last bowel movement was 2 days ago, which is not severe enough to cause acute urinary retention of this magnitude.
- The primary cause of his urinary symptoms is more likely related to bladder outflow obstruction rather than external compression from constipation.
*Urinary tract infection*
- A UTI typically presents with symptoms like **dysuria**, **frequency**, **urgency**, **fever**, and **chills**, none of which are prominent here.
- While a UTI can cause some urinary difficulty, it's less likely to be the sole cause of such acute and severe urinary retention or a bladder volume of 750 mL without other infection signs.
*Worsening benign prostatic hypertrophy*
- Although the patient has BPH and is on finasteride, a **sudden dramatic worsening** over 3 days, leading to complete inability to void and a large bladder volume, is less typical for a gradual disease progression.
- The acute change points more strongly to an **exacerbating factor**, such as a new medication, rather than a natural progression of BPH.
Question 233: A 62-year-old woman is referred to a tertiary care hospital with a history of diplopia and fatigue for the past 3 months. She has also noticed difficulty in climbing the stairs and combing her hair. She confirms a history of 2.3 kg (5.0 lb) weight loss in the past 6 weeks and constipation. Past medical history is significant for type 2 diabetes mellitus. She has a 50-pack-year cigarette smoking history. Physical examination reveals a blood pressure of 135/78 mm Hg supine and 112/65 while standing, a heart rate of 82/min supine and 81/min while standing, and a temperature of 37.0°C (98.6°F). She is oriented to time and space. Her right upper eyelid is slightly drooped. She has difficulty in abducting the right eye. Pupils are bilaterally equal and reactive to light with accommodation. The corneal reflex is intact. Muscle strength is reduced in the proximal muscles of all 4 limbs, and the lower limbs are affected more when compared to the upper limbs. Deep tendon reflexes are bilaterally absent. After 10 minutes of cycling, the reflexes become positive. Sensory examination is normal. Diffuse wheezes are heard on chest auscultation. Which of the following findings is expected?
A. Thymoma on CT scan of the chest
B. Incremental pattern on repetitive nerve conduction studies (Correct Answer)
C. Periventricular plaques on MRI of the brain
D. Antibodies against muscle-specific kinase
E. Elevated serum creatine kinase
Explanation: ***Incremental pattern on repetitive nerve conduction studies***
- The patient's symptoms (diplopia, fatigue, proximal muscle weakness, absent reflexes that normalize with exercise) are highly suggestive of **Lambert-Eaton myasthenic syndrome (LEMS)**.
- LEMS is characterized by impaired acetylcholine release at the neuromuscular junction, which manifests as an **incremental response** (progressively larger muscle action potentials) during high-frequency repetitive nerve stimulation.
*Thymoma on CT scan of the chest*
- **Thymoma** is strongly associated with **myasthenia gravis**, which typically presents with fluctuating weakness that worsens with activity and improves with rest, unlike the LEMS presentation.
- While LEMS can be paraneoplastic, it is most commonly associated with **small cell lung carcinoma**, not thymoma, making this finding less likely.
*Periventricular plaques on MRI of the brain*
- **Periventricular plaques** are characteristic findings in **multiple sclerosis**, a demyelinating disease of the central nervous system.
- Multiple sclerosis presents with diverse neurological deficits, but not typically with this specific pattern of fluctuating muscle weakness and absent deep tendon reflexes that improve with exercise.
*Antibodies against muscle-specific kinase*
- **Anti-MuSK antibodies** are associated with a specific subtype of **myasthenia gravis**, often presenting with prominent bulbar and respiratory weakness.
- While myasthenic syndromes share some features, the specific clinical picture (especially the improvement of reflexes with exercise) points away from standard myasthenia gravis and towards LEMS.
*Elevated serum creatine kinase*
- **Elevated creatine kinase** is typically seen in **myopathies** (e.g., inflammatory myopathies, muscular dystrophies) where there is direct muscle damage.
- In LEMS, the primary defect is at the neuromuscular junction, not within the muscle itself, so creatine kinase levels are usually normal.
Question 234: A 42-year-old woman comes to the physician because of progressive weakness. She has noticed increasing difficulty performing household chores and walking her dog over the past month. Sometimes she feels too fatigued to cook dinner. She has noticed that she feels better after sleeping. She does not have chest pain, shortness of breath, or a history of recent illness. She has no personal history of serious illness and takes no medications. She has smoked two packs of cigarettes daily for 25 years. She appears fatigued. Her temperature is 37°C (98.8°F), pulse is 88/min, and blood pressure is 148/80 mm Hg. Pulse oximetry shows an oxygen saturation of 98% in room air. Bilateral expiratory wheezes are heard at both lung bases. Examination shows drooping of the upper eyelids. There is diminished motor strength in her upper extremities. Her sensation and reflexes are intact. A treatment with which of the following mechanisms of action is most likely to be effective?
A. Stimulation of β2 adrenergic receptors
B. Competitive blocking of the muscarinic receptor
C. Reactivation of acetylcholinesterase
D. Inhibition of acetylcholinesterase (Correct Answer)
E. Removing autoantibodies, immune complexes, and cytotoxic constituents from serum
Explanation: ***Inhibition of acetylcholinesterase***
- The patient's symptoms of **progressive weakness**, **fatigue that improves with rest** (improves after sleeping), **bilateral ptosis (drooping eyelids)**, and **diminished motor strength** are classic signs of **myasthenia gravis**.
- **Myasthenia gravis** is an autoimmune disorder where antibodies block or destroy acetylcholine receptors at the neuromuscular junction; inhibiting **acetylcholinesterase** increases acetylcholine availability, improving muscle strength.
*Stimulation of B2 adrenergic receptors*
- This mechanism is primarily used to treat **bronchospasm** in conditions like **asthma** or **COPD**, corresponding to the expiratory wheezes, but would not address the systemic muscle weakness and ptosis.
- While beta-agonists can alleviate respiratory symptoms, they do not target the underlying pathophysiology of **myasthenia gravis**.
*Competitive blocking of the muscarinic receptor*
- **Muscarinic receptor blockers** like **ipratropium** are used to treat bronchoconstriction, often in **COPD**, by preventing acetylcholine from binding to muscarinic receptors on smooth muscle in the airways.
- This mechanism would not improve the skeletal muscle weakness and ptosis seen in **myasthenia gravis**, as these symptoms are related to nicotinic receptors at the neuromuscular junction, not muscarinic receptors.
*Reactivation of acetylcholinesterase*
- **Reactivation of acetylcholinesterase** would lead to a more rapid breakdown of acetylcholine, further *reducing* its availability at the neuromuscular junction.
- This action would worsen the symptoms of **myasthenia gravis** by further impairing neuromuscular transmission.
*Removing autoantibodies, immune complexes, and cytotoxic constituents from serum*
- This describes **plasmapheresis** (plasma exchange), which is a rapid, temporary treatment for myasthenia gravis, particularly during myasthenic crisis or before surgery.
- While effective in severe cases by reducing circulating antibodies, it's not the primary or initial mechanism of action for *pharmacological* therapy, which usually involves **acetylcholinesterase inhibitors** or immunotherapy.
Question 235: In an attempt to create other selective dopamine 1 (D1) agonists, a small pharmaceutical company created a cell-based chemical screen that involved three modified receptors - alpha 1 (A1), beta 1 (B1), and D1. In the presence of D1 stimulation, the cell would produce an mRNA that codes for a fluorescent protein; however, if the A1 or B1 receptors are also stimulated at the same time, the cells would degrade the mRNA of the fluorescent protein thereby preventing it from being produced. Which of the following would best serve as a positive control for this experiment?
A. Fenoldopam (Correct Answer)
B. Dobutamine
C. Epinephrine
D. Bromocriptine
E. Dopamine
Explanation: ***Fenoldopam***
- **Fenoldopam** is a selective **D1 dopamine receptor agonist** with minimal affinity for alpha-adrenergic receptors and no significant beta-adrenergic activity.
- Its selectivity for D1 receptors means it would stimulate only D1, leading to **fluorescent protein mRNA production** without triggering degradation via A1 or B1 pathways, serving as an ideal positive control for D1 stimulation.
*Dobutamine*
- **Dobutamine** is a **beta-1 adrenergic receptor agonist**, primarily used to increase cardiac contractility.
- Its strong B1 activity would lead to degradation of the fluorescent protein mRNA, making it unsuitable as a positive control for D1 stimulation.
*Epinephrine*
- **Epinephrine** (adrenaline) is a potent agonist at **alpha-1, alpha-2, beta-1, and beta-2 adrenergic receptors**.
- Its broad receptor activation, including A1 and B1, would cause the degradation of the fluorescent protein mRNA, thus failing to act as a positive control for D1.
*Bromocriptine*
- **Bromocriptine** is primarily a **D2 dopamine receptor agonist**, used in conditions like Parkinson's disease and hyperprolactinemia.
- It has minimal or no affinity for D1, A1, or B1 receptors at therapeutic concentrations, so it would not induce fluorescent protein mRNA production, nor would it cause its degradation.
*Dopamine*
- **Dopamine** acts on multiple receptors, including **D1, D2, alpha-1, and beta-1 adrenergic receptors** in a dose-dependent manner.
- Its concurrent stimulation of D1, A1, and B1 receptors would lead to both mRNA production and subsequent degradation, making it difficult to isolate D1 activity and therefore not an ideal positive control here.
Question 236: A 48-year-old man is unable to pass urine after undergoing open abdominal surgery. His physical examination and imaging findings suggest that the cause of his urinary retention is non-obstructive and is most probably due to urinary bladder atony. He is prescribed a new selective muscarinic (M3) receptor agonist, which improves his symptoms. Which of the following is most likely involved in the mechanism of action of this new drug?
A. Activation of phospholipase C (Correct Answer)
B. Inhibition of guanylyl cyclase
C. Inhibition of adenylyl cyclase
D. Increased transmembrane K+ conductance
E. Increased transmembrane Na+ conductance
Explanation: ***Activation of phospholipase C***
- **M3 receptors** are Gq protein-coupled receptors, and their activation leads to the stimulation of **phospholipase C**.
- **Phospholipase C** hydrolyzes **phosphatidylinositol 4,5-bisphosphate (PIP2)** into **inositol trisphosphate (IP3)** and **diacylglycerol (DAG)**, which ultimately increases intracellular Ca2+ and causes smooth muscle contraction in the bladder.
*Inhibition of guanylyl cyclase*
- **Guanylyl cyclase** is typically modulated by other pathways, such as **nitric oxide (NO)**, leading to cGMP production and smooth muscle relaxation.
- Its inhibition would not be the primary mechanism for a muscarinic M3 agonist aiming to contract the bladder.
*Inhibition of adenylyl cyclase*
- **Adenylyl cyclase** is typically inhibited by Gi-coupled receptors (e.g., M2 receptors) leading to a decrease in cAMP and muscle relaxation, which is the opposite effect desired in bladder atony.
- M3 receptors, which are Gq-coupled, do not directly inhibit adenylyl cyclase.
*Increased transmembrane K+ conductance*
- **Increased K+ conductance** typically leads to hyperpolarization and relaxation of smooth muscle, which would worsen bladder atony rather than improve it.
- This mechanism is not associated with direct M3 receptor activation.
*Increased transmembrane Na+ conductance*
- While Na+ channels play a role in neuronal excitability, a direct effect on **transmembrane Na+ conductance** is not the primary mechanism of action for M3 receptor agonists in causing bladder smooth muscle contraction.
- Smooth muscle contraction primarily involves **calcium influx and release**.
Question 237: A 31-year-old woman is brought to the physician because of increasing restlessness over the past 2 weeks. She reports that she continuously paces around the house and is unable to sit still for more than 10 minutes at a time. During this period, she has had multiple episodes of anxiety with chest tightness and shortness of breath. She was diagnosed with a psychotic illness 2 months ago. Her current medications include haloperidol and a multivitamin. She appears agitated. Vital signs are within normal limits. Physical examination shows no abnormalities. The examination was interrupted multiple times when she became restless and began to walk around the room. To reduce the likelihood of the patient developing her current symptoms, a drug with which of the following mechanisms of action should have been prescribed instead of her current medication?
A. H2 receptor antagonism
B. 5-HT2A receptor antagonism (Correct Answer)
C. α2 receptor antagonism
D. NMDA receptor antagonism
E. GABA receptor antagonism
Explanation: ***5-HT2A receptor antagonism***
- The patient is experiencing **akathisia**, a common extrapyramidal side effect of **typical antipsychotics** like haloperidol, characterized by subjective or objective motor restlessness.
- Atypical antipsychotics, which exert their antipsychotic effects primarily through **5-HT2A receptor antagonism** along with D2 receptor antagonism, have a lower propensity to cause extrapyramidal symptoms, including akathisia, compared to typical antipsychotics.
*H2 receptor antagonism*
- **H2 receptor antagonists** are primarily used to reduce gastric acid secretion in conditions like peptic ulcer disease and GERD.
- They have no direct role in treating psychosis or preventing extrapyramidal side effects.
*α2 receptor antagonism*
- **Alpha-2 receptor antagonists** (e.g., mirtazapine) are typically used as antidepressants; their mechanism involves increasing norepinephrine and serotonin release.
- This mechanism is not directly therapeutic for psychosis and would not prevent akathisia caused by D2 receptor blockade.
*NMDA receptor antagonism*
- **NMDA receptor antagonists** (e.g., ketamine, memantine) are studied for various neurological and psychiatric conditions, but their primary use is not in typical psychosis treatment, nor do they prevent akathisia from antipsychotics.
- Instead, NMDA receptor hypofunction is hypothesized in schizophrenia, and antagonism could potentially worsen psychotic symptoms.
*GABA receptor antagonism*
- **GABA receptor antagonists** (e.g., flumazenil) block the effects of inhibitory neurotransmitter GABA and can cause seizures and increased anxiety, which would be detrimental in a patient with psychosis and anxiety.
- Medications that *enhance* GABAergic transmission (e.g., benzodiazepines) are sometimes used to treat acute akathisia or anxiety, but long-term antagonism would be contra-indicated.
Question 238: A 23-year-old man presents to the emergency department with shortness of breath. The patient was at a lunch hosted by his employer. He started to feel his symptoms begin when he started playing football outside with a few of the other employees. The patient has a past medical history of atopic dermatitis and asthma. His temperature is 98.3°F (36.8°C), blood pressure is 87/58 mmHg, pulse is 150/min, respirations are 22/min, and oxygen saturation is 85% on room air. Which of the following is the best next step in management?
A. Albuterol and prednisone
B. IV epinephrine
C. IV fluids and 100% oxygen
D. Albuterol and norepinephrine
E. IM epinephrine (Correct Answer)
Explanation: ***IM epinephrine***
- The patient presents with **signs of anaphylaxis**, including acute onset shortness of breath, hypotension (BP 87/58 mmHg), tachycardia (HR 150/min), and hypoxia (SpO2 85%). Given his history of atopic dermatitis and asthma, he is at high risk for severe allergic reactions.
- **Intramuscular epinephrine** is the first-line treatment for anaphylaxis as it acts rapidly to constrict blood vessels, relax airway smooth muscle, and reduce swelling, addressing both cardiovascular collapse and respiratory distress.
*Albuterol and prednisone*
- While **albuterol** (a bronchodilator) might help with bronchoconstriction, and **prednisone** (a corticosteroid) can reduce inflammation, these are not the immediate priority for severe anaphylaxis.
- They act too slowly to counteract the rapid, systemic effects of anaphylaxis, particularly the life-threatening hypotension and airway compromise.
*IV epinephrine*
- **Intravenous epinephrine** is reserved for severe, refractory cases of anaphylaxis, or for patients already receiving IV infusions in a critical care setting.
- Administering IV epinephrine requires careful titration due to the risk of arrhythmias and hypertension, and IM administration is preferred as the initial rapid response.
*IV fluids and 100% oxygen*
- **IV fluids** are crucial to address the distributive shock and hypotension in anaphylaxis, and **100% oxygen** is essential for hypoxia, but these are supportive measures.
- They do not address the underlying immunological mechanism driving the severe allergic reaction as directly and effectively as epinephrine.
*Albuterol and norepinephrine*
- **Albuterol** can help with bronchospasm, but it is insufficient for systemic anaphylaxis. **Norepinephrine** is a potent vasopressor used for severe shock.
- While norepinephrine can raise blood pressure, it does not have the broader beneficial effects of epinephrine on mast cell degranulation, airway dilation, and stabilization of vascular permeability, making it a secondary agent.
Question 239: A 65-year-old patient with a history of COPD and open-angle glaucoma in the left eye has had uncontrolled intraocular pressure (IOP) for the last few months. She is currently using latanoprost eye drops. Her ophthalmologist adds another eye drop to her regimen to further decrease her IOP. A week later, the patient returns because of persistent dim vision. On exam, she has a small fixed pupil in her left eye as well as a visual acuity of 20/40 in her left eye compared to 20/20 in her right eye. Which of the following is the mechanism of action of the medication most likely prescribed in this case?
A. Increasing the permeability of sclera to aqueous humor
B. Inhibiting the production of aqueous humor by the ciliary epithelium
C. Closing the trabecular mesh by relaxing the ciliary muscles
D. Opening the canal of Schlemm by contracting the ciliary muscle (Correct Answer)
E. Increasing reabsorption of aqueous humor by the ciliary epithelium
Explanation: **Correct Answer: Opening the canal of Schlemm by contracting the ciliary muscle**
- The clinical presentation of a **small fixed pupil (miosis)** and **dim vision** strongly suggests the patient was prescribed a **cholinergic agonist** (e.g., pilocarpine), which acts by stimulating muscarinic M3 receptors.
- Cholinergic agonists cause **ciliary muscle contraction**, which pulls on the scleral spur, widening the **trabecular meshwork** spaces and increasing outflow of aqueous humor through the **canal of Schlemm**, thereby lowering IOP.
- The **miosis** (pupillary constriction) and **accommodative spasm** causing dim vision are characteristic side effects of muscarinic agonists.
*Incorrect: Increasing the permeability of sclera to aqueous humor*
- This mechanism does not correspond to any commonly prescribed **glaucoma medication** and is not a primary mechanism for IOP regulation.
- The sclera serves as an anatomical boundary, not a primary site of aqueous humor outflow regulation.
*Incorrect: Inhibiting the production of aqueous humor by the ciliary epithelium*
- **Beta-blockers** (e.g., timolol) and **carbonic anhydrase inhibitors** (e.g., dorzolamide, acetazolamide) work by decreasing aqueous humor production.
- These medications do **not** cause **miosis** (pupil constriction) or the dim vision seen in this patient, which are hallmark side effects of cholinergic agonists.
*Incorrect: Closing the trabecular mesh by relaxing the ciliary muscles*
- Relaxation of the ciliary muscles would **narrow the trabecular meshwork**, which would **decrease aqueous humor outflow** and **increase** IOP, contradicting the goal of glaucoma treatment.
- This mechanism would not explain the **small fixed pupil** seen in this patient.
*Incorrect: Increasing reabsorption of aqueous humor by the ciliary epithelium*
- The **ciliary epithelium** is primarily responsible for the **production** of aqueous humor via active secretion, not its reabsorption.
- Aqueous humor is removed through the **trabecular meshwork** (conventional outflow) and the **uveoscleral pathway** (unconventional outflow), not by ciliary epithelial reabsorption.
Question 240: A 5-year-old boy is brought to the emergency department by his parents for difficulty breathing. He was playing outside in the snow and had progressive onset of wheezing and gasping. His history is notable for eczema and nut allergies. The patient has respirations of 22/min and is leaning forward with his hands on his legs as he is seated on the table. Physical examination is notable for inspiratory and expiratory wheezes on exam. A nebulized medication is started and begins to relieve his breathing difficulties. Which of the following is increased in this patient as a result of this medication?
A. Cyclic GMP
B. Diacylglycerol
C. ATP
D. Protein kinase C
E. Cyclic AMP (Correct Answer)
Explanation: ***Correct: Cyclic AMP***
- The patient presents with an acute asthma exacerbation, likely triggered by cold weather and his atopic history (eczema, nut allergies). The nebulized medication is most likely a **beta-2 agonist** (e.g., albuterol), which acts by stimulating **adenylate cyclase**.
- This stimulation leads to an increase in intracellular **cyclic AMP (cAMP)**, which activates protein kinase A (PKA). PKA then phosphorylates various targets, leading to **bronchodilation** by relaxing airway smooth muscle.
*Incorrect: Cyclic GMP*
- **Cyclic GMP (cGMP)** is primarily involved in smooth muscle relaxation via nitric oxide signaling, not typically the target of bronchodilators used for acute asthma exacerbations.
- While some drugs like **nitrates** increase cGMP, bronchodilators like albuterol do not act through this pathway.
*Incorrect: Diacylglycerol*
- **Diacylglycerol (DAG)** is a secondary messenger produced by the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) by phospholipase C.
- It is involved in various cell signaling pathways, including the activation of **protein kinase C (PKC)**, but it is not directly increased by beta-2 agonists.
*Incorrect: Protein kinase C*
- **Protein kinase C (PKC)** is a family of enzymes activated by calcium and **diacylglycerol (DAG)**, playing roles in cell growth, differentiation, and metabolism.
- Beta-2 agonists do not directly increase PKC activity; rather, they activate the adenylyl cyclase-cAMP-PKA pathway.
*Incorrect: ATP*
- **ATP (adenosine triphosphate)** is the cellular energy currency and is not specifically increased by beta-2 agonist therapy.
- While ATP is the substrate for adenylate cyclase to produce cAMP, beta-2 agonists do not increase ATP levels themselves.
