A 35-year-old female presents to her primary care physician because of chronic fatigue that has stopped her from gardening and walking with her friends. Upon further questioning, she elaborates that she feels fine after waking up but gradually becomes more tired and weak as the day progresses. This appears to be particularly problematic when she is engaged in physical activity or when eating. Review of systems elicits that she occasionally experiences double vision after spending a prolonged period looking at a computer screen. Testing confirms the diagnosis and the patient is prescribed a long-acting medication to alleviate her symptoms. The products of the enzyme that is inhibited by the prescribed drug are transported by a protein that is sensitive to which of the following chemicals?
Q142
A 23-year-old man is brought to the emergency department from a college party because of a 1-hour history of a crawling sensation under his skin. He appears anxious and is markedly pale. His temperature is 38°C (100.4°F), pulse is 104/min, respirations are 18/min, and blood pressure is 145/90 mm Hg. Physical examination shows diaphoretic skin, moist mucous membranes, and dilated pupils. Which of the following substances is most likely the cause of this patient's symptoms?
Q143
A 22-year-old man is brought to the emergency department 10 minutes after falling down a flight of stairs. An x-ray of the right wrist shows a distal radius fracture. A rapidly acting intravenous anesthetic agent is administered, and closed reduction of the fracture is performed. Following the procedure, the patient reports palpitations and says that he experienced an “extremely vivid dream,” in which he felt disconnected from himself and his surroundings while under anesthesia. His pulse is 110/min and blood pressure is 140/90 mm Hg. The patient was most likely administered a drug that predominantly blocks the effects of which of the following neurotransmitters?
Q144
A 19-year-old man is seen by his primary care physician. The patient has a history of excessive daytime sleepiness going back several years. He has begun experiencing episodes in which his knees become weak and he drops to the floor when he laughs. He has a history of marijuana use. His family history is notable for hypertension and cardiac disease. His primary care physician refers him for a sleep study, which confirms your suspected diagnosis.
Which of the following is the best first-line pharmacological treatment for this patient?
Q145
A 58-year-old man comes to the physician for a 2-month history of increased urinary frequency. Urodynamic testing shows a urinary flow rate of 11 mL/s (N>15) and a postvoid residual volume of 65 mL (N<50). Prostate-specific antigen level is 3.2 ng/mL (N<4). Treatment with a drug that also increases scalp hair regrowth is initiated. Which of the following is the most likely mechanism of action of this drug?
Q146
A 26-year-old woman presents with an 8-month history of insomnia and anxiety. She says that she has difficulty sleeping and has feelings of impending doom linked to her difficult financial situation. No significant family history and no current medications. The patient was prescribed an 8-week supply of medication. She follows up 4 weeks later saying that she has increased anxiety and needs a refill. She says that over the past month, due to increasing anxiety levels, she started taking extra doses of her medication to achieve an anxiolytic effect. Which of the following medications was most likely prescribed to this patient?
Q147
A 16-year-old boy is brought to the emergency department by ambulance with a visible deformity of the upper thigh after being involved in a motor vehicle collision. He is informed that he will require surgery and is asked about his medical history. He mentions that he had surgery to remove his tonsils several years ago and at that time suffered a complication during the surgery. Specifically, shortly after the surgery began, he began to experience severe muscle contractions and an increased body temperature. Based on this information, a different class of muscle relaxants are chosen for use during the upcoming surgery. If these agents needed to be reversed, the reversal agent should be administered with which of the following to prevent off-target effects?
Q148
A 43-year-old male with a history of thyroid cancer status post total thyroidectomy presents to his primary care physician after repeated bouts of headaches. His headaches are preceded by periods of anxiety, palpitations, and sweating. The patient says he is unable to pinpoint any precipitating factors and instead says the events occur without warning. Of note, the patient's father and uncle also have a history of thyroid cancer. On exam his vitals are: T 36.8 HR 87, BP 135/93, RR 14, and O2 Sat 100% on room air. The patient's TSH is within normal limits, and he reports taking his levothyroxine as prescribed. What is the next best step in diagnosing this patient's chief complaint?
Q149
A 16-year-old woman is brought to the emergency department by her family for not being responsive. The patient had locked herself in her room for several hours after breaking up with her boyfriend. When her family found her, they were unable to arouse her and immediately took her to the hospital. The patient has a past medical history of anorexia nervosa, which is being treated, chronic pain, and depression. She is not currently taking any medications. The patient has a family history of depression in her mother and grandmother. IV fluids are started, and the patient seems to be less somnolent. Her temperature is 101°F (38.3°C), pulse is 112/min, blood pressure is 90/60 mmHg, respirations are 18/min, and oxygen saturation is 95% on room air. On physical exam, the patient is somnolent and has dilated pupils and demonstrates clonus. She has dry skin and an ultrasound of her bladder reveals 650 mL of urine. The patient is appropriately treated with sodium bicarbonate. Which of the following is the best indicator of the extent of this patient's toxicity?
Q150
A 32-year-old man with a history of alcohol binge drinking and polysubstance use is found down in his hotel room with bottles of alcohol, oxycodone, alprazolam, amphetamine-dextroamphetamine, and tadalafil. When EMS arrives, he appears comatose with pinpoint pupils and oxygen saturation of 80% on room air. He is intubated at the scene and airlifted to the nearest intensive care unit. Body temperature is 95 degrees F (35 degrees C). Creatine phosphokinase is 12,000 U/L. MRI of the brain demonstrates extensive infarcts consistent with acute hypoxic ischemic injury. Which of the following is the likely culprit for his overdose?
Cholinergic/Adrenergic drugs US Medical PG Practice Questions and MCQs
Question 141: A 35-year-old female presents to her primary care physician because of chronic fatigue that has stopped her from gardening and walking with her friends. Upon further questioning, she elaborates that she feels fine after waking up but gradually becomes more tired and weak as the day progresses. This appears to be particularly problematic when she is engaged in physical activity or when eating. Review of systems elicits that she occasionally experiences double vision after spending a prolonged period looking at a computer screen. Testing confirms the diagnosis and the patient is prescribed a long-acting medication to alleviate her symptoms. The products of the enzyme that is inhibited by the prescribed drug are transported by a protein that is sensitive to which of the following chemicals?
A. Guanethidine
B. Hemicholinium (Correct Answer)
C. Vesamicol
D. Botulinum
E. Reserpine
Explanation: ***Hemicholinium***
- The clinical presentation of **fatigue worsening with activity and throughout the day**, along with **double vision**, is highly suggestive of **myasthenia gravis**.
- **Pyridostigmine**, a long-acting **acetylcholinesterase inhibitor**, is used to treat myasthenia gravis, increasing acetylcholine at the neuromuscular junction for improved muscle strength. The question asks about the transport of the products of the enzyme inhibited by Pyridostigmine. Acetylcholinesterase breaks down acetylcholine into choline and acetate. Hence, it is asking about **choline transport**. **Hemicholinium** is a drug that inhibits the high-affinity reuptake of choline into the presynaptic neuron, disrupting acetylcholine synthesis.
*Guanethidine*
- **Guanethidine** is a **sympathetic neuron blocker** that inhibits the release of norepinephrine from adrenergic nerve terminals.
- It does not directly affect acetylcholine synthesis or transport, which is the focus of the question.
*Vesamicol*
- **Vesamicol** blocks the **vesicular acetylcholine transporter (VAChT)**, preventing acetylcholine from being packaged into synaptic vesicles.
- While it affects acetylcholine storage, it does not directly inhibit choline reuptake, which is the specific mechanism relevant to the question.
*Botulinum*
- **Botulinum toxin** prevents the release of acetylcholine from presynaptic terminals by cleaving SNARE proteins, leading to muscle paralysis.
- Its action is on **acetylcholine release**, not on the transport of its precursor (choline) or breakdown products.
*Reserpine*
- **Reserpine** depletes **monoamine neurotransmitters** (norepinephrine, dopamine, serotonin) by inhibiting their uptake into storage vesicles.
- It is primarily associated with adrenergic and serotonergic pathways, not cholinergic transmission.
Question 142: A 23-year-old man is brought to the emergency department from a college party because of a 1-hour history of a crawling sensation under his skin. He appears anxious and is markedly pale. His temperature is 38°C (100.4°F), pulse is 104/min, respirations are 18/min, and blood pressure is 145/90 mm Hg. Physical examination shows diaphoretic skin, moist mucous membranes, and dilated pupils. Which of the following substances is most likely the cause of this patient's symptoms?
A. Scopolamine
B. Phencyclidine
C. Cocaine (Correct Answer)
D. Oxycodone
E. Lysergic acid diethylamide
Explanation: ***Cocaine***
- The patient's symptoms of **anxiety**, **diaphoresis**, **mydriasis (dilated pupils)**, and **tachycardia** are consistent with **sympathomimetic toxicity**, commonly seen with cocaine use.
- The **crawling sensation under the skin (formication)**, also known as "cocaine bugs," is a classic symptom of significant cocaine intoxication.
*Scopolamine*
- Scopolamine is an **anticholinergic** agent, causing symptoms like **dry mouth**, **dilated pupils**, and **tachycardia**, but typically also causes dry skin and urinary retention.
- It would not usually present with diaphoresis or the specific crawling sensation.
*Phencyclidine*
- **Phencyclidine (PCP)** intoxication characteristically causes **nystagmus**, **ataxia**, and often leads to **violent behavior** or **agitation**, which are not the primary features described here.
- While it can cause hallucinations and psychosis, the "crawling sensation" is less typical for PCP compared to cocaine.
*Oxycodone*
- **Oxycodone** is an **opioid**, which would typically cause **miosis (constricted pupils)**, **respiratory depression**, and **sedation**, directly contradicting the patient's symptoms.
- It would not lead to anxiety, tachycardia, or diaphoresis in the manner described.
*Lysergic acid diethylamide*
- **Lysergic acid diethylamide (LSD)** is a **hallucinogen** known for causing marked perceptual distortions, vivid hallucinations, and altered thought processes.
- While it can cause autonomic symptoms like sweating and tachycardia, the specific "crawling sensation" is not a hallmark symptom of LSD, and the clinical picture is more suggestive of sympathomimetic overload.
Question 143: A 22-year-old man is brought to the emergency department 10 minutes after falling down a flight of stairs. An x-ray of the right wrist shows a distal radius fracture. A rapidly acting intravenous anesthetic agent is administered, and closed reduction of the fracture is performed. Following the procedure, the patient reports palpitations and says that he experienced an “extremely vivid dream,” in which he felt disconnected from himself and his surroundings while under anesthesia. His pulse is 110/min and blood pressure is 140/90 mm Hg. The patient was most likely administered a drug that predominantly blocks the effects of which of the following neurotransmitters?
A. Endorphin
B. Dopamine
C. Norepinephrine
D. Glutamate (Correct Answer)
E. Gamma-aminobutyric acid
Explanation: ***Glutamate***
- The patient's symptoms of **dissociative anesthesia**, **vivid dreams**, and **palpitations** are characteristic of **ketamine**, which is a rapidly acting intravenous anesthetic.
- Ketamine works primarily as a **non-competitive antagonist of the NMDA receptor**, blocking the excitatory effects of glutamate.
*Endorphin*
- Endorphins are **endogenous opioid peptides** that act on opioid receptors, producing analgesia and euphoria.
- Drugs acting predominantly on endorphin pathways (e.g., opioids) do not typically cause dissociative states or vivid dreams as described.
*Dopamine*
- Dopamine is involved in reward, motivation, and motor control; drugs affecting dopamine (e.g., antipsychotics, Parkinson's medications) have different primary effects.
- Blocking dopamine would not directly produce dissociative anesthesia or the cardiovascular and hallucinatory side effects seen with ketamine.
*Norepinephrine*
- Norepinephrine is a neurotransmitter involved in the **sympathetic nervous system** and its effects on alertness, vigilance, and the fight-or-flight response.
- While ketamine can cause sympathetic stimulation leading to increased heart rate and blood pressure, its primary mechanism of anesthesia is not through norepinephrine blockade.
*Gamma-aminobutyric acid*
- **Gamma-aminobutyric acid (GABA)** is the main inhibitory neurotransmitter in the CNS, and drugs that enhance GABAergic activity (e.g., benzodiazepines, propofol) typically cause sedation, anxiolysis, and amnesia.
- This patient's symptoms of vivid dreams and dissociation are opposite to the effects of GABAergic anesthetics, which often produce unconsciousness without such mental experiences.
Question 144: A 19-year-old man is seen by his primary care physician. The patient has a history of excessive daytime sleepiness going back several years. He has begun experiencing episodes in which his knees become weak and he drops to the floor when he laughs. He has a history of marijuana use. His family history is notable for hypertension and cardiac disease. His primary care physician refers him for a sleep study, which confirms your suspected diagnosis.
Which of the following is the best first-line pharmacological treatment for this patient?
A. Zolpidem
B. Lisdexamfetamine
C. Modafinil (Correct Answer)
D. Methylphenidate
E. Dextroamphetamine
Explanation: ***Modafinil***
- This patient presents with symptoms of **narcolepsy** (excessive daytime sleepiness, cataplexy triggered by laughter). **Modafinil** is a non-amphetamine stimulant and a **first-line treatment** for the **excessive daytime sleepiness** component of narcolepsy due to its efficacy in improving wakefulness with a relatively low side effect profile.
- It works by increasing the release of **monoamines (norepinephrine, dopamine, serotonin)** and histamine, promoting wakefulness without significant cardiovascular effects or abuse potential compared to traditional stimulants.
- **Note:** While modafinil addresses the daytime sleepiness, **cataplexy** would typically require additional treatment with **sodium oxybate** (first-line for cataplexy) or antidepressants (SSRIs, SNRIs, or TCAs).
*Zolpidem*
- **Zolpidem** is a **sedative-hypnotic** primarily used for the short-term treatment of **insomnia**, not for excessive daytime sleepiness or narcolepsy.
- Administering a sedative would worsen the patient's primary complaint of daytime sleepiness.
*Lisdexamfetamine*
- **Lisdexamfetamine** is a **prodrug of dextroamphetamine**, a potent central nervous system stimulant used for **ADHD** and sometimes narcolepsy.
- While effective, it is generally considered a **second-line treatment** for narcolepsy after non-amphetamine stimulants like modafinil, especially given its higher potential for abuse and side effects.
*Methylphenidate*
- **Methylphenidate** is a **central nervous system stimulant** commonly used for **ADHD** and, in some cases, narcolepsy.
- Similar to lisdexamfetamine, it is a stronger stimulant with greater potential for side effects and abuse compared to modafinil, making it a less preferred first-line option.
*Dextroamphetamine*
- **Dextroamphetamine** is a potent **amphetamine stimulant** effective for increasing wakefulness in narcolepsy.
- However, due to its **higher abuse potential**, cardiovascular side effects, and more significant impact on dopamine pathways, it is usually reserved for cases refractory to safer options like modafinil.
Question 145: A 58-year-old man comes to the physician for a 2-month history of increased urinary frequency. Urodynamic testing shows a urinary flow rate of 11 mL/s (N>15) and a postvoid residual volume of 65 mL (N<50). Prostate-specific antigen level is 3.2 ng/mL (N<4). Treatment with a drug that also increases scalp hair regrowth is initiated. Which of the following is the most likely mechanism of action of this drug?
A. Gonadotropin-releasing hormone receptor agonism
B. Decreased conversion of hydroxyprogesterone to androstenedione
C. Decreased conversion of testosterone to dihydrotestosterone (Correct Answer)
D. Decreased conversion of testosterone to estradiol
E. Selective alpha-1A/D receptor antagonism
Explanation: ***Decreased conversion of testosterone to dihydrotestosterone***
- The patient's symptoms (urinary frequency), urodynamic findings (low flow rate, elevated postvoid residual), and slightly elevated PSA are consistent with **benign prostatic hyperplasia (BPH)**.
- A drug that treats BPH and also increases **scalp hair regrowth** is a **5α-reductase inhibitor** (e.g., finasteride), which works by blocking the conversion of testosterone to dihydrotestosterone (DHT), the primary androgen responsible for prostate growth and androgenetic alopecia.
*Gonadotropin-releasing hormone receptor agonism*
- GnRH agonists (e.g., leuprolide) are used for advanced **prostate cancer** by initially stimulating and then desensitizing GnRH receptors, leading to decreased testosterone production.
- They do not promote scalp hair regrowth but can cause **testicular atrophy** and **hot flashes**.
*Decreased conversion of hydroxyprogesterone to androstenedione*
- This pathway is involved in the synthesis of androgens in the adrenal glands and gonads but is not the primary mechanism targeted by drugs used for BPH with hair regrowth benefits.
- Drugs acting at this step are not typically associated with BPH treatment or hair regrowth.
*Decreased conversion of testosterone to estradiol*
- This refers to the action of **aromatase inhibitors** (e.g., anastrozole), which block the conversion of androgens to estrogens.
- Aromatase inhibitors are used in the treatment of **hormone-sensitive breast cancer** and do not treat BPH or promote scalp hair regrowth.
*Selective alpha-1A/D receptor antagonism*
- **Alpha-1 blockers** (e.g., tamsulosin) relax the smooth muscle in the prostate and bladder neck, improving urinary flow in BPH.
- While effective for BPH, they do not impact **hair regrowth** and may cause orthostatic hypotension or ejaculatory dysfunction.
Question 146: A 26-year-old woman presents with an 8-month history of insomnia and anxiety. She says that she has difficulty sleeping and has feelings of impending doom linked to her difficult financial situation. No significant family history and no current medications. The patient was prescribed an 8-week supply of medication. She follows up 4 weeks later saying that she has increased anxiety and needs a refill. She says that over the past month, due to increasing anxiety levels, she started taking extra doses of her medication to achieve an anxiolytic effect. Which of the following medications was most likely prescribed to this patient?
A. Triazolam (Correct Answer)
B. Hydroxyzine
C. Zolpidem
D. Buspirone
E. Propranolol
Explanation: ***Triazolam***
- Triazolam is a **short-acting benzodiazepine** commonly prescribed for insomnia, but its rapid onset and short duration can lead to **rebound anxiety** and dependence with chronic use, as seen with the patient's increased anxiety and need for a refill.
- The patient's need to take "extra doses...to achieve an anxiolytic effect" suggests the development of **tolerance** and dependence, which is characteristic of benzodiazepine misuse.
*Hydroxyzine*
- Hydroxyzine is a **first-generation antihistamine** with sedative and anxiolytic properties, often used for anxiety and insomnia due to its relatively low abuse potential.
- It does not typically cause the **rapid tolerance** and withdrawal symptoms (like increased anxiety needing extra doses) seen with benzodiazepines.
*Zolpidem*
- Zolpidem is a **non-benzodiazepine hypnotic** (Z-drug) that acts on GABA-A receptors and is commonly prescribed for insomnia.
- While it has **lower dependence potential** than benzodiazepines, the patient's presentation with rapid tolerance development and dose escalation for anxiolytic effect is more characteristic of **benzodiazepine use** rather than zolpidem, which primarily provides sedation without strong anxiolytic effects.
*Buspirone*
- Buspirone is an **anxiolytic** that works on serotonin receptors and is used for generalized anxiety disorder, but it has a **delayed onset of action** (weeks) and lacks the immediate anxiolytic effect that would lead to acute dose escalation.
- It has a **low potential for abuse** or dependence, making it an unlikely choice for a patient rapidly escalating doses for an immediate effect.
*Propranolol*
- Propranolol is a **beta-blocker** used to manage the physical symptoms of anxiety (e.g., tremors, palpitations), but it does not directly treat the psychological symptoms of anxiety or insomnia.
- It is not associated with **tolerance, dependence**, or the need for dose escalation to achieve an anxiolytic effect.
Question 147: A 16-year-old boy is brought to the emergency department by ambulance with a visible deformity of the upper thigh after being involved in a motor vehicle collision. He is informed that he will require surgery and is asked about his medical history. He mentions that he had surgery to remove his tonsils several years ago and at that time suffered a complication during the surgery. Specifically, shortly after the surgery began, he began to experience severe muscle contractions and an increased body temperature. Based on this information, a different class of muscle relaxants are chosen for use during the upcoming surgery. If these agents needed to be reversed, the reversal agent should be administered with which of the following to prevent off-target effects?
A. Atropine (Correct Answer)
B. Epinephrine
C. Echothiophate
D. Methacholine
E. Phentolamine
Explanation: **Atropine**
- The patient's history of **severe muscle contractions** and **increased body temperature** during prior surgery indicates **malignant hyperthermia**, a contraindication for succinylcholine
- Therefore, **nondepolarizing neuromuscular blockers** will be used instead and reversal is typically achieved with **neostigmine** (acetylcholinesterase inhibitor)
- Neostigmine increases acetylcholine at **both nicotinic and muscarinic receptors**, causing undesirable **muscarinic side effects** (bradycardia, salivation, bronchospasm, increased GI motility)
- **Atropine** or **glycopyrrolate** (muscarinic antagonists) must be co-administered to prevent these off-target muscarinic effects
*Epinephrine*
- Sympathomimetic acting on **alpha- and beta-adrenergic receptors** used for anaphylaxis, severe asthma, and cardiac arrest
- Not used to prevent muscarinic side effects of acetylcholinesterase inhibitors
*Echothiophate*
- **Irreversible acetylcholinesterase inhibitor** used for glaucoma treatment
- Would exacerbate rather than prevent cholinergic side effects when combined with neostigmine
*Methacholine*
- **Muscarinic cholinergic agonist** used in bronchial challenge tests for asthma diagnosis
- Would worsen muscarinic side effects rather than preventing them
*Phentolamine*
- **Alpha-adrenergic blocker** used for hypertensive crises from pheochromocytoma or vasopressor extravasation
- No role in managing muscarinic side effects of acetylcholinesterase inhibitors
Question 148: A 43-year-old male with a history of thyroid cancer status post total thyroidectomy presents to his primary care physician after repeated bouts of headaches. His headaches are preceded by periods of anxiety, palpitations, and sweating. The patient says he is unable to pinpoint any precipitating factors and instead says the events occur without warning. Of note, the patient's father and uncle also have a history of thyroid cancer. On exam his vitals are: T 36.8 HR 87, BP 135/93, RR 14, and O2 Sat 100% on room air. The patient's TSH is within normal limits, and he reports taking his levothyroxine as prescribed. What is the next best step in diagnosing this patient's chief complaint?
A. 24-hour urine free cortisol
B. Plasma aldosterone/renin ratio
C. Abdominal CT scan with and without IV contrast
D. Plasma fractionated metanephrines (Correct Answer)
E. High dose dexamethasone suppression test
Explanation: ***Plasma fractionated metanephrines***
- The patient's symptoms of **anxiety, palpitations, sweating, and headaches** occurring in discrete "attacks" are classic for a **pheochromocytoma**, a tumor that secretes catecholamines.
- Given the patient's and his family's history of **thyroid cancer**, specifically likely **medullary thyroid cancer** due to the familial link, there is a high suspicion for **Multiple Endocrine Neoplasia type 2 (MEN2)**, which commonly includes pheochromocytoma. **Plasma fractionated metanephrines** are the most sensitive screening test for pheochromocytoma.
*24-hour urine free cortisol*
- This test is used to detect **Cushing's syndrome**, which involves excessive cortisol production.
- Although Cushing's can cause **hypertension**, the paroxysmal symptoms of anxiety, palpitations, and sweating are not typical of Cushing's syndrome.
*Plasma aldosterone/renin ratio*
- This ratio is used to screen for **primary hyperaldosteronism**, a cause of secondary hypertension.
- While the patient has **hypertension (135/93 mm Hg)**, his symptom complex of episodic anxiety, palpitations, and sweating is not characteristic of primary hyperaldosteronism.
*Abdominal CT scan with and without IV contrast*
- An abdominal CT scan can visualize adrenal masses, but it is typically performed *after* biochemical confirmation of a pheochromocytoma to localize the tumor.
- Performing imaging before biochemical testing risks incidentalomas or missing a biochemically active but small tumor, and it is not the most appropriate *next step* in diagnosis given the strong clinical suspicion.
*High dose dexamethasone suppression test*
- This test is specifically used to differentiate between **Cushing's disease** (pituitary ACTH excess) and other causes of Cushing's syndrome.
- The patient's symptoms are not consistent with excessive cortisol production, making this test inappropriate for his chief complaint.
Question 149: A 16-year-old woman is brought to the emergency department by her family for not being responsive. The patient had locked herself in her room for several hours after breaking up with her boyfriend. When her family found her, they were unable to arouse her and immediately took her to the hospital. The patient has a past medical history of anorexia nervosa, which is being treated, chronic pain, and depression. She is not currently taking any medications. The patient has a family history of depression in her mother and grandmother. IV fluids are started, and the patient seems to be less somnolent. Her temperature is 101°F (38.3°C), pulse is 112/min, blood pressure is 90/60 mmHg, respirations are 18/min, and oxygen saturation is 95% on room air. On physical exam, the patient is somnolent and has dilated pupils and demonstrates clonus. She has dry skin and an ultrasound of her bladder reveals 650 mL of urine. The patient is appropriately treated with sodium bicarbonate. Which of the following is the best indicator of the extent of this patient's toxicity?
A. QRS prolongation (Correct Answer)
B. QT prolongation
C. Serum drug level
D. Anion gap acidosis
E. Liver enzyme elevation
Explanation: ***QRS prolongation***
- This patient's symptoms (including **hyperthermia**, **tachycardia**, **hypotension**, **dilated pupils**, **somnolence**, and **clonus**) along with her history of depression suggest **tricyclic antidepressant (TCA) toxicity**.
- **QRS prolongation** on an EKG (greater than 100 ms) is the most reliable indicator of severe TCA toxicity and predicts the risk of **seizures** and **ventricular arrhythmias**.
*QT prolongation*
- While some drugs cause QT prolongation, **TCA toxicity** primarily causes sodium channel blockade leading to **QRS widening**, which is a more critical indicator of immediate cardiotoxicity risk.
- QT prolongation is seen in toxicities involving potassium channel blockade, which is not the primary mechanism of severe TCA cardiotoxicity.
*Serum drug level*
- **Serum drug levels** of TCAs do not reliably correlate with the severity of toxicity due to variable metabolism, protein binding, and individual patient sensitivity.
- Clinical signs and EKG findings are more important in guiding management.
*Anion gap acidosis*
- Although **metabolic acidosis** can occur in severe overdose, it is not specific to TCA toxicity and is a less direct indicator of the immediate cardiotoxic and neurotoxic risk compared to QRS prolongation.
- Anion gap can be elevated due to various reasons in a critically ill patient.
*Liver enzyme elevation*
- **Liver enzyme elevation** is not an immediate or primary indicator of acute TCA overdose severity.
- Liver toxicity can occur with chronic use or some specific drug overdoses, but it is not the most pertinent marker for acute, life-threatening TCA toxicity.
Question 150: A 32-year-old man with a history of alcohol binge drinking and polysubstance use is found down in his hotel room with bottles of alcohol, oxycodone, alprazolam, amphetamine-dextroamphetamine, and tadalafil. When EMS arrives, he appears comatose with pinpoint pupils and oxygen saturation of 80% on room air. He is intubated at the scene and airlifted to the nearest intensive care unit. Body temperature is 95 degrees F (35 degrees C). Creatine phosphokinase is 12,000 U/L. MRI of the brain demonstrates extensive infarcts consistent with acute hypoxic ischemic injury. Which of the following is the likely culprit for his overdose?
A. Amphetamines
B. Phosphodiesterase-5 (PDE-5) inhibitors
C. Alcohol
D. Benzodiazepines
E. Opioids (Correct Answer)
Explanation: ***Opioids***
- The patient's presentation with **pinpoint pupils**, **respiratory depression** (oxygen saturation 80%, requiring intubation), and coma is highly characteristic of **opioid overdose**.
- **Hypothermia** and **rhabdomyolysis** (elevated CK) are common complications of severe opioid toxicity due to prolonged immobility and hypoperfusion.
*Amphetamines*
- Amphetamine overdose typically causes **mydriasis (dilated pupils)**, **tachycardia**, **hypertension**, and **hyperthermia**, which are contrary to the patient's presentation.
- While amphetamines can cause rhabdomyolysis and altered mental status, the pinpoint pupils and hypothermia rule it out as the primary cause of his comatose state.
*Phosphodiesterase-5 (PDE-5) inhibitors*
- PDE-5 inhibitors like tadalafil primarily cause **vasodilation**, which can lead to **hypotension**, headaches, and flushing.
- They do not typically cause **respiratory depression**, **pinpoint pupils**, or coma, making it an unlikely culprit for this severe presentation.
*Alcohol*
- While excessive alcohol consumption can cause **CNS depression**, coma, and respiratory depression, it typically results in **dilated or normal pupils**, not pinpoint pupils.
- The combination of pinpoint pupils and severe respiratory depression points more strongly towards opioid toxicity.
*Benzodiazepines*
- Benzodiazepine overdose causes **CNS depression**, respiratory depression, and coma, but typically presents with **normal or slightly dilated pupils**.
- While benzodiazepines can exacerbate opioid effects, the classic **pinpoint pupils** are the key differentiating factor pointing to opioids.