A 28-year-old woman secretary complains of fatigue that increases throughout the day. At the end of her workday, she says her eyes feel “heavy” and “droopy,” although she does not feel particularly tired. Pyridostigmine is prescribed to treat her myasthenia gravis. How does pyridostigmine work?

Correct Answer: A

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: C

Rationale: A pure opioid antagonist binds opioid receptors (primarily mu) without activating them, reversing agonist effects. Naloxone (choice C) is the gold standard, used in opioid overdose to rapidly reverse respiratory depression and sedation by competitively blocking receptors. Methadone (choice A) is a full mu agonist, used for pain and addiction maintenance, not antagonism. Nalbuphine (choice B) is a mixed agonist-antagonist, with kappa agonism and mu antagonism, not pure. Buprenorphine (choice D) is a partial mu agonist with high affinity, used in addiction treatment, not a pure antagonist. Naloxone's pure antagonistic action distinguishes it, making it essential in emergencies to counteract opioid toxicity, unlike mixed or agonist drugs.

Correct Answer: B

Rationale: NSAIDs (e.g., ibuprofen, aspirin) inhibit cyclo-oxygenase (COX) enzymes (choice B), reducing prostaglandin synthesis, which mediates inflammation, pain, and fever. Cholinesterase (choice A) is targeted by anticholinesterases, not NSAIDs. Lipo-oxygenase (choice C) produces leukotrienes, unaffected by most NSAIDs. Phosphodiesterase (choice D) relates to cAMP, irrelevant here. COX inhibition is the unifying mechanism, critical for understanding NSAID effects and side effects like GI irritation.

Correct Answer: A

Rationale: Morphine treats acute abdominal pain (choice A), like postoperative pain, via mu agonism, though diagnosis is key due to masking. Head injury (choice B) contraindicates it due to respiratory depression and ICP rise. Bronchial asthma (choice C) worsens with respiratory suppression. Neurogenic shock (choice D) isn't a primary indication. Acute pain aligns with morphine's analgesic role.

Correct Answer: A

Rationale: Allopurinol (choice A) reduces serum and urinary uric acid by inhibiting xanthine oxidase, preventing urate formation, ideal for chronic gout post-acute attack. Colchicine (choice B) and Indomethacin (choice C) treat acute inflammation, not uric acid levels. Probenecid (choice D) increases urinary uric acid excretion, not decreasing it. Allopurinol fits the description for long-term gout management.