We have a 48-year-old female patient with a history of myasthenia gravis. She has been treated with an oral acetylcholinesterase inhibitor for several years and has done well till now. She presents with muscle weakness and other signs and symptoms that could reflect either a cholinergic crisis (excess dosages of her maintenance drug) or a myasthenic crisis (insufficient treatment). We will use a rapidly acting parenteral acetylcholinesterase inhibitor (AChE) to help make the differential diagnosis. Which of the following drugs would be most appropriate for this use?

Correct Answer: A

Rationale: The correct answer is A: Edrophonium. Edrophonium is a short-acting acetylcholinesterase inhibitor that can help differentiate between a cholinergic crisis and a myasthenic crisis. In this scenario, administering edrophonium will temporarily increase acetylcholine levels at the neuromuscular junction. If the patient's symptoms improve following edrophonium administration, it suggests a myasthenic crisis due to insufficient treatment. On the other hand, if the symptoms worsen, it indicates a cholinergic crisis due to excess dosages of the maintenance drug. Choice B: Malathion is an organophosphate insecticide and is not used for diagnosing myasthenia gravis. Choice C: Physostigmine is a longer-acting acetylcholinesterase inhibitor and is not appropriate for rapidly assessing the patient's condition in this scenario. Choice D: Pralidoxime is used as an antidote for organophosphate

Correct Answer: C

Rationale: The correct answer is C: Organic phosphate. Pralidoxime is used to treat toxicity caused by organophosphates, which inhibit cholinesterase enzymes. Pralidoxime works by reactivating the inhibited cholinesterase enzymes, restoring their function. Atropine is used to counteract the effects of excessive acetylcholine in cholinergic toxicity, not organophosphate poisoning. Nicotine is a nicotinic receptor agonist and not treated with pralidoxime. Amphetamine is a central nervous system stimulant and does not involve cholinesterase inhibition. Therefore, the correct answer is C as pralidoxime is specifically used to treat toxicity caused by organophosphates.

Correct Answer: B

Rationale: The correct answer is B: Prazosin. α-1 adrenergic receptors are selectively blocked by prazosin. Prazosin is a selective α-1 adrenergic receptor antagonist, specifically targeting these receptors. It works by blocking the effects of norepinephrine, leading to vasodilation and reduced blood pressure. A: Phentolamine is a non-selective α-adrenergic receptor antagonist, blocking both α-1 and α-2 receptors. C: Propranolol is a non-selective β-adrenergic receptor antagonist, blocking β-1 and β-2 receptors. D: Ergotamine is a medication used for the treatment of migraines and has vasoconstrictive properties but does not selectively block α-1 adrenergic receptors.

Correct Answer: D

Rationale: The correct answer is D because physostigmine is used in the treatment of glaucoma due to its ability to lower intraocular pressure. It works by inhibiting the enzyme acetylcholinesterase, leading to increased levels of acetylcholine which helps in constricting the pupil and improving drainage of fluid in the eye. Options A and C are incorrect as physostigmine is a tertiary amine and a reversible anti-cholinesterase. Option B is incorrect as physostigmine does have CNS action, crossing the blood-brain barrier and affecting brain function.

Correct Answer: D

Rationale: The correct answer is D because anticholinesterase drugs are not bronchodilators; they actually increase cholinergic activity by inhibiting the breakdown of acetylcholine. Reversible and irreversible types do exist (A), neostigmine and physostigmine are examples (B), and they can cause miosis and lacrimation due to increased cholinergic activity (C). Hence, D is the incorrect statement.