All questions
Question 1
A 45-year-old man with a long history of schizophrenia, previously managed with haloperidol, is switched to a new medication due to persistent negative symptoms. Six months later, his fasting glucose is 135 mg/dL and he has gained 11 kg (25 lb). His psychotic symptoms, however, have improved. The new medication is discontinued due to these metabolic changes.
The beneficial effects and metabolic side effects of this new medication are most likely mediated by its antagonist activity at which combination of receptors?
- Dopamine D2 and Serotonin 5-HT2A receptors (correct answer)
- Dopamine D2 receptors only
- Muscarinic M1 and Histamine H1 receptors
- Norepinephrine and Serotonin transporters
Explanation: This patient developed metabolic syndrome (weight gain, hyperglycemia) after being switched to a new antipsychotic, which is characteristic of atypical (second-generation) antipsychotics like olanzapine or clozapine. These agents exert their therapeutic effects and are also responsible for their metabolic side effect profile through combined antagonism of dopamine D2 and serotonin 5-HT2A receptors. Blockade of H1 and muscarinic receptors also contributes to weight gain and other side effects, but the core antipsychotic and metabolic mechanism involves D2 and 5-HT2A.
Question 2
A 55-year-old woman being treated for atypical depression with phenelzine is brought to the emergency department with a severe headache, palpitations, and a blood pressure of 210/120 mm Hg. She reports that her symptoms began shortly after attending a wine and cheese party. She has been compliant with her medication regimen.
This patient's hypertensive crisis is a result of the prescribed medication inhibiting an enzyme that normally metabolizes which of the following substances found in the consumed food and beverage?
- Tyramine (correct answer)
- Tryptophan
- Glutamate
- Histamine
Explanation: Phenelzine is a monoamine oxidase (MAO) inhibitor. MAO is responsible for breaking down dietary catecholamines like tyramine, which is found in aged cheeses, cured meats, and red wine. When MAO is inhibited, ingested tyramine is not metabolized, leading to a massive release of stored catecholamines (norepinephrine, epinephrine) from nerve terminals, causing a severe hypertensive crisis.
Question 3
An 82-year-old woman with generalized anxiety disorder is prescribed a low dose of lorazepam. A week later, her daughter brings her to the clinic because she has become increasingly confused, forgetful, and has had two falls. The physician suspects the new medication is responsible for these symptoms.
This medication exerts its anxiolytic and adverse cognitive effects by which of the following mechanisms?
- Increasing the frequency of chloride channel opening on the GABAA receptor (correct answer)
- Increasing the duration of chloride channel opening on the GABAA receptor
- Directly activating the GABAA receptor at the GABA binding site
- Blocking voltage-gated sodium channels in the CNS
Explanation: Lorazepam is a benzodiazepine. Benzodiazepines are positive allosteric modulators of the GABAA receptor. They bind to a site distinct from the GABA binding site and increase the frequency of chloride channel opening when GABA is bound. This enhances the inhibitory effect of GABA, leading to sedation, anxiolysis, and cognitive impairment, particularly in the elderly. Barbiturates increase the duration of channel opening.
Question 4
A 34-year-old man undergoes an open reduction and internal fixation of a tibial fracture. Postoperatively, he is started on a patient-controlled analgesia pump with morphine. While his pain is well-controlled, he complains of significant constipation by the second postoperative day. He has no prior history of gastrointestinal issues.
This common adverse effect of morphine is primarily mediated by the activation of which receptors in the enteric nervous system?
- Muscarinic M3 receptors
- Serotonin 5-HT3 receptors
- μ-opioid receptors (correct answer)
- α2-adrenergic receptors
Explanation: Opioids like morphine cause constipation by activating μ-opioid receptors in the myenteric plexus of the gastrointestinal tract. This activation inhibits the release of acetylcholine from nerve endings, leading to decreased smooth muscle motility, reduced peristalsis, and increased colonic transit time, resulting in constipation.
Question 5
A 68-year-old man with Parkinson disease is treated with a combination of levodopa and carbidopa. His bradykinesia and rigidity improve significantly. He experiences mild nausea but avoids the severe vomiting and cardiac arrhythmias that can occur with levodopa alone.
What is the primary mechanism by which carbidopa enhances the therapeutic effect of levodopa and reduces its peripheral side effects?
- It inhibits peripheral aromatic L-amino acid decarboxylase. (correct answer)
- It directly stimulates dopamine receptors in the striatum.
- It blocks the reuptake of dopamine in the synaptic cleft.
- It inhibits catechol-O-methyltransferase (COMT) in the brain.
Explanation: Carbidopa is an inhibitor of peripheral aromatic L-amino acid decarboxylase (also known as DOPA decarboxylase). This enzyme converts levodopa to dopamine. By inhibiting this enzyme in the periphery, carbidopa prevents the conversion of levodopa to dopamine outside the central nervous system. This increases the amount of levodopa that can cross the blood-brain barrier and be converted to dopamine in the brain, while reducing peripheral side effects like nausea, vomiting, and arrhythmias caused by peripheral dopamine.
Question 6
A 22-year-old man with a history of generalized tonic-clonic seizures is being managed with an antiepileptic drug. During a routine dental visit, the dentist notes significant gingival hyperplasia. The patient also mentions that he has noticed increased growth of coarse hair on his face and trunk.
The medication responsible for these findings most likely exerts its anticonvulsant effect by which of the following mechanisms?
- Inhibition of T-type calcium channels
- Blockade of voltage-gated sodium channels (correct answer)
- Potentiation of GABAA receptor-mediated inhibition
- Irreversible inhibition of GABA transaminase
Explanation: Gingival hyperplasia and hirsutism are classic side effects of phenytoin. Phenytoin is a primary antiepileptic drug that works by blocking voltage-gated sodium channels in their inactivated state. This action prolongs the refractory period of the neuron, preventing the rapid, repetitive firing that characterizes seizures.
Question 7
A 28-year-old man is started on sertraline for major depressive disorder. After six weeks of treatment, his mood has improved significantly, but he reports new-onset difficulty achieving orgasm, which he finds distressing. He has no other medical problems and takes no other medications.
This adverse effect is a well-known complication of medications that increase the synaptic concentration of which neurotransmitter?
- Dopamine
- Norepinephrine
- Serotonin (correct answer)
- Acetylcholine
Explanation: Sertraline is a selective serotonin reuptake inhibitor (SSRI). SSRIs work by blocking the presynaptic serotonin transporter (SERT), leading to increased levels of serotonin in the synaptic cleft. Stimulation of various serotonin receptors, particularly 5-HT2 and 5-HT3, is responsible for the common side effect of sexual dysfunction, including decreased libido, delayed ejaculation, and anorgasmia.
Question 8
A 30-year-old woman is undergoing a brief surgical procedure for which desflurane, an inhaled anesthetic, is used. The anesthesiologist notes that both the induction of and emergence from anesthesia are very rapid. The patient is awake and alert shortly after the anesthetic is discontinued.
The rapid onset and recovery associated with this anesthetic agent are best explained by which of its physicochemical properties?
- High blood:gas partition coefficient
- Low blood:gas partition coefficient (correct answer)
- High minimum alveolar concentration (MAC)
- Extensive hepatic metabolism
Explanation: The speed of induction and recovery for an inhaled anesthetic is inversely proportional to its solubility in blood, which is measured by the blood:gas partition coefficient. Anesthetics with a low blood:gas partition coefficient (like desflurane and nitrous oxide) are less soluble in blood. This means that the partial pressure of the gas in the alveoli equilibrates very quickly with the partial pressure in the blood and brain, leading to rapid induction and rapid elimination upon discontinuation.
Question 9
A 35-year-old man with acute psychosis is started on haloperidol. Within a week, he develops a slow, shuffling gait, a resting tremor in his right hand, and a noticeable lack of facial expression. His wife states he seems 'stiff as a board.'
These extrapyramidal symptoms are a direct consequence of haloperidol's antagonist activity at which of the following receptors in the nigrostriatal pathway?
- Serotonin 5-HT2A receptors
- Histamine H1 receptors
- Muscarinic M1 receptors
- Dopamine D2 receptors (correct answer)
Explanation: Haloperidol is a high-potency typical (first-generation) antipsychotic that exerts its effects primarily through potent antagonism of dopamine D2 receptors. Blockade of D2 receptors in the mesolimbic pathway is therapeutic for positive psychotic symptoms. However, blockade of D2 receptors in the nigrostriatal pathway disrupts the normal balance of dopamine and acetylcholine, leading to an excess of cholinergic activity and producing extrapyramidal symptoms (EPS) such as parkinsonism (bradykinesia, rigidity, tremor) as seen in this patient.
Question 10
A 9-year-old boy is diagnosed with attention-deficit/hyperactivity disorder (ADHD). He is started on methylphenidate. After several weeks, his parents and teacher report a significant improvement in his ability to focus on tasks and a reduction in hyperactive and impulsive behaviors.
What is the primary mechanism of action of methylphenidate in treating ADHD?
- Selective inhibition of norepinephrine reuptake
- Blockade of presynaptic dopamine and norepinephrine transporters (correct answer)
- Increased release of dopamine and norepinephrine from presynaptic vesicles
- Direct agonism of postsynaptic D2 dopamine receptors
Explanation: Methylphenidate is a CNS stimulant used to treat ADHD. Its primary mechanism of action is the blockade of the dopamine transporter (DAT) and norepinephrine transporter (NET). This inhibition of reuptake increases the synaptic concentrations of dopamine and norepinephrine, particularly in the prefrontal cortex, which is thought to enhance executive function, attention, and impulse control.
Question 11
A dentist injects lidocaine, a local anesthetic, to numb a patient's gum before a procedure. However, the injection is administered into an area of inflamed, abscessed tissue. The patient reports that the anesthetic effect is much weaker than expected.
The reduced efficacy of the local anesthetic in this setting is best explained by which of the following?
- Inflamed tissue has a low extracellular pH, which increases the proportion of the cationic form of the drug. (correct answer)
- Bacterial enzymes in the abscess rapidly metabolize the lidocaine.
- Increased blood flow to the inflamed area enhances systemic absorption.
- Inflamed tissue has a high extracellular pH, which prevents the drug from binding to sodium channels.
Explanation: Local anesthetics are weak bases. To be effective, they must cross the lipid-rich nerve membrane in their non-ionized (uncharged) form. Once inside the neuron, they re-equilibrate, and the ionized (cationic) form blocks the intracellular side of the voltage-gated sodium channel. Infected and inflamed tissues are acidic (have a low extracellular pH). This acidic environment protonates the weak base anesthetic, increasing the proportion of the ionized, cationic form. The charged form cannot effectively cross the nerve membrane, leading to reduced anesthetic efficacy.
Question 12
An 80-year-old man with postherpetic neuralgia is prescribed low-dose amitriptyline. While it helps his pain, he complains of a persistently dry mouth, difficulty urinating, and constipation. On examination, his pupils are noted to be dilated.
These adverse effects are caused by the drug's antagonist activity at which of the following receptors?
- α1-adrenergic receptors
- Dopamine D2 receptors
- Muscarinic acetylcholine receptors (correct answer)
- Histamine H1 receptors
Explanation: Amitriptyline is a tricyclic antidepressant (TCA) with strong anticholinergic properties. The symptoms described—dry mouth (xerostomia), urinary retention, constipation, and mydriasis (dilated pupils)—are classic signs of muscarinic receptor blockade. These effects result from the inhibition of parasympathetic nervous system activity throughout the body.
Question 13
A 27-year-old woman with epilepsy is well-controlled on valproic acid. She and her partner are planning a pregnancy and she consults her neurologist for preconception counseling. The physician discusses the significant teratogenic risks associated with her current medication.
In utero exposure to valproic acid is most strongly associated with an increased risk for which of the following congenital malformations?
- Limb reduction defects
- Ebstein anomaly
- Cleft palate
- Neural tube defects (correct answer)
Explanation: Valproic acid is a known human teratogen. Its use during the first trimester of pregnancy is associated with a significantly increased risk of major congenital malformations, most notably neural tube defects such as spina bifida. The mechanism is thought to involve inhibition of folate absorption and metabolism, which is critical for neural tube closure.
Question 14
A 75-year-old woman is diagnosed with mild Alzheimer disease after her family notes progressive memory loss over the past year. She is started on donepezil. Her family is counseled that the medication may offer a modest, temporary improvement in cognitive function.
This medication aims to improve cognitive symptoms by increasing the synaptic availability of which neurotransmitter?
- Norepinephrine
- Dopamine
- Serotonin
- Acetylcholine (correct answer)
Explanation: Donepezil is an acetylcholinesterase inhibitor. In Alzheimer disease, there is a significant loss of cholinergic neurons, leading to a deficit of acetylcholine in brain regions critical for memory and cognition. By inhibiting acetylcholinesterase, the enzyme that breaks down acetylcholine, donepezil increases the amount and duration of action of acetylcholine in the synaptic cleft, thereby enhancing cholinergic transmission and providing modest symptomatic relief.
Question 15
A 48-year-old man with bipolar I disorder has been maintained on lithium for several years. He presents to his physician complaining of constant thirst, frequent urination, and a persistent fine tremor in his hands. Laboratory studies show a normal serum glucose and a serum sodium of 143 mEq/L. His lithium level is within the therapeutic range.
Lithium is thought to produce both its therapeutic and certain adverse effects, such as nephrogenic diabetes insipidus, by interfering with which of the following signaling pathways?
- Tyrosine kinase receptor pathway
- Janus kinase (JAK)-STAT pathway
- Inositol phosphate signaling pathway (correct answer)
- Nuclear hormone receptor pathway
Explanation: The proposed mechanism of action for lithium involves the inhibition of enzymes in the inositol phosphate signaling pathway, such as inositol monophosphatase. This depletes intracellular inositol, which dampens the signaling of Gq-protein coupled receptors, including certain adrenergic, muscarinic, and serotonergic receptors. Interference with this pathway in the renal collecting duct cells, specifically with the V2 receptor signaling for ADH, leads to nephrogenic diabetes insipidus, causing polyuria and polydipsia.
Question 16
A 40-year-old accountant with generalized anxiety disorder expresses concern about the sedative effects and abuse potential of benzodiazepines. His physician prescribes an anxiolytic that is not a benzodiazepine, does not cause significant sedation, and is not a controlled substance. The patient is advised that the medication may take 2-4 weeks to become fully effective.
Which of the following represents the most likely mechanism of action of the prescribed drug?
- Partial agonism at serotonin 5-HT1A receptors (correct answer)
- Non-selective beta-adrenergic receptor blockade
- Irreversible inhibition of monoamine oxidase
- Antagonism at histamine H1 receptors
Explanation: The clinical scenario describes the key features of buspirone. Buspirone is an anxiolytic used for generalized anxiety disorder that is unique because it is not a benzodiazepine, lacks sedative and hypnotic effects, and has no abuse potential. Its mechanism of action is as a partial agonist at presynaptic and postsynaptic serotonin 5-HT1A receptors. It also has some antagonist activity at dopamine D2 receptors. The delayed onset of action is characteristic of this medication.
Question 17
A 32-year-old woman with bipolar II disorder is started on a mood stabilizer. The dose is titrated slowly over several weeks. However, three weeks into treatment, she develops a fever, sore throat, and a diffuse, targetoid rash on her trunk, face, and palms. She is hospitalized with a diagnosis of Stevens-Johnson syndrome.
Which of the following medications, which acts by inhibiting voltage-gated sodium channels, is most likely responsible for this life-threatening dermatologic reaction?
- Lithium
- Valproic acid
- Lamotrigine (correct answer)
- Quetiapine
Explanation: Lamotrigine is an antiepileptic and mood-stabilizing drug whose mechanism involves blockade of voltage-gated sodium channels. It carries a black box warning for potentially life-threatening rashes, including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). The risk is highest when the initial dose is high or the dose is escalated too rapidly, which is why a slow titration schedule is crucial.
Question 18
A 58-year-old man with a long history of alcohol use disorder is admitted to the hospital for an elective cholecystectomy. On the second day of admission, he becomes agitated, diaphoretic, and tremulous. He experiences visual hallucinations and a generalized tonic-clonic seizure. His blood pressure is 180/100 mm Hg and heart rate is 120/min.
This patient's withdrawal syndrome is primarily caused by the downregulation of inhibitory neurotransmission and upregulation of excitatory neurotransmission. The acute symptoms are best explained by a sudden lack of ethanol-mediated potentiation of which receptor system?
- Dopamine D2 receptors
- NMDA glutamate receptors
- GABAA receptors (correct answer)
- Serotonin 5-HT1A receptors
Explanation: Chronic ethanol use potentiates the effect of GABA at GABAA receptors, leading to increased chloride influx and CNS inhibition. To compensate, the body downregulates GABAA receptors. Concurrently, ethanol inhibits NMDA glutamate receptors, and the body compensates by upregulating them. Upon abrupt cessation of alcohol, the system is left in a hyperexcitable state: there is reduced GABAergic inhibition and excessive glutamatergic excitation, leading to the symptoms of alcohol withdrawal, including seizures and delirium tremens.
Question 19
A 22-year-old man is brought to the emergency department after being found unresponsive by his friends. On examination, his respiratory rate is 4/min, pupils are 1 mm and nonreactive to light, and he has track marks on his arms. He is immediately given an intravenous bolus of naloxone, and his respiratory rate and level of consciousness improve within one minute.
How does naloxone reverse the life-threatening effects of the opioid overdose?
- It acts as a partial agonist at μ-opioid receptors, displacing the full agonist.
- It is a competitive antagonist with high affinity for μ-opioid receptors. (correct answer)
- It accelerates the hepatic metabolism of the opioid via cytochrome P450.
- It directly stimulates the respiratory centers in the brainstem.
Explanation: The patient's presentation of respiratory depression, pinpoint pupils (miosis), and unresponsiveness is classic for an opioid overdose. Naloxone is a pure, competitive antagonist at all opioid receptors (μ, κ, and δ), with the highest affinity for the μ-receptor. When administered, it rapidly displaces the opioid agonist (e.g., heroin, fentanyl) from these receptors, particularly in the brainstem respiratory centers, thereby reversing the life-threatening respiratory depression.
Question 20
A 24-year-old woman is brought to the emergency department by her roommate, who found her lethargic and difficult to arouse. The patient has slurred speech, ataxia, and mild respiratory depression. An empty bottle of alprazolam is found nearby. An intravenous medication is administered, and the patient's level of consciousness rapidly improves.
The antidote administered to this patient, flumazenil, reverses the sedative effects by which mechanism?
- Competitive antagonism at the benzodiazepine binding site on the GABAA receptor (correct answer)
- Competitive antagonism at the μ-opioid receptor
- Non-competitive antagonism at the barbiturate binding site on the GABAA receptor
- Increasing the hepatic metabolism of benzodiazepines via P450 induction
Explanation: This patient presents with a benzodiazepine (alprazolam) overdose. The specific antidote is flumazenil. Flumazenil is a competitive antagonist that binds with high affinity to the benzodiazepine binding site on the GABAA receptor. By occupying this site, it prevents benzodiazepines from binding and enhancing the effects of GABA, thereby rapidly reversing the CNS and respiratory depression.