A 43-year-old woman with diagnosed myasthenia gravis presents with profound skeletal muscle weakness. We are unsure whether she is experiencing a cholinergic crisis or a myasthenic crisis, so we administer a usually appropriate dose of parenteral edrophonium. Assume the patient was actually experiencing a cholinergic crisis. Which of the following is the most likely response to the drug?

Correct Answer: D

Rationale: The correct answer is D: Ventilatory distress or failure. Edrophonium is a short-acting acetylcholinesterase inhibitor used to differentiate between myasthenic and cholinergic crises. In a cholinergic crisis, which is an excess of acetylcholine, administering edrophonium can worsen symptoms due to further acetylcholine accumulation. This can lead to excessive stimulation of the respiratory muscles, resulting in ventilatory distress or failure. Choice A is incorrect because cholinergic crisis typically causes hypotension, not hypertension. Choice B is incorrect because edrophonium-induced tachycardia can worsen myocardial ischemia, not angina. Choice C is incorrect because increased ventricular automaticity would not be a common response to edrophonium in a cholinergic crisis.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Adrenaline causes vasoconstriction leading to increased blood pressure. 2. Prazosin is an alpha-1 adrenergic receptor antagonist. 3. By blocking alpha-1 receptors, prazosin reverses the vasoconstrictive effects of adrenaline. 4. Propranolol (A) is a non-selective beta-blocker and would not directly counteract adrenaline's vasoconstrictive effects. 5. Phenylephrine (B) is a vasoconstrictor itself and would further exacerbate the hypertensive effect of adrenaline. 6. Amphetamine (D) is a sympathomimetic drug that would also enhance the hypertensive effects of adrenaline. Summary: Prazosin (C) is the correct answer as it specifically targets the alpha-1 adrenergic receptors responsible for the hypertensive effects of adrenaline. Propranolol, phenylephrine, and amphetamine would

Correct Answer: C

Rationale: Atropine is used in the treatment of intestinal colic due to its ability to relax smooth muscles, including those in the gastrointestinal tract. It helps relieve spasms and pain associated with intestinal colic. Tachycardia is usually treated with beta-blockers, not atropine. Glaucoma is treated with medications that reduce intraocular pressure, not atropine. Enlarged prostate is typically managed with medications that target prostate enlargement, not atropine. Therefore, the correct choice is C: Intestinal colic.

Correct Answer: C

Rationale: Rationale: C: Prazosin can block Alpha1 receptor only. - Prazosin is a selective Alpha1 blocker, mainly used for hypertension. - By blocking Alpha1 receptors, it reduces vasoconstriction and lowers blood pressure. - Prazosin does not affect Alpha2 receptors, distinguishing it from non-selective Alpha blockers. - Correct as it accurately describes Prazosin's mechanism of action. Incorrect: A: Phentolamine is a non-selective Alpha blocker, affecting both Alpha1 and Alpha2 receptors. B: Alpha2 blockers increase noradrenaline release by inhibiting the negative feedback control. D: Alpha blockers typically decrease blood pressure, but can increase heart rate due to vasodilation.

Correct Answer: B

Rationale: Step-by-step rationale for why B (Carbachol) is the correct answer: 1. Carbachol is a cholinergic drug that acts on both muscarinic and nicotinic receptors. 2. It is resistant to hydrolysis by both true and pseudo cholinesterase enzymes. 3. Acetylcholine (A) is rapidly hydrolyzed by both cholinesterases. 4. Bethanechol (C) is a muscarinic agonist but not a nicotinic agonist. 5. Succinylcholine (D) is a depolarizing neuromuscular blocking agent, not a cholinergic agonist. Summary: Carbachol is the only drug among the choices that has both muscarinic and nicotinic actions and is resistant to hydrolysis by cholinesterases. Acetylcholine is rapidly hydrolyzed, Bethanechol does not have nicotinic actions, and Succinyl