Which of the following direct-acting cholinomimetics has the shortest duration of action?

Correct Answer: A

Rationale: Step 1: Acetylcholine is a direct-acting cholinomimetic that quickly hydrolyzes by acetylcholinesterase, leading to a short duration of action. Step 2: Methacholine, Carbachol, and Bethanechol are also direct-acting cholinomimetics but are more resistant to enzymatic degradation, resulting in longer durations of action. Summary: Acetylcholine has the shortest duration of action due to rapid enzymatic degradation compared to the other choices. Methacholine, Carbachol, and Bethanechol have longer durations of action as they are more resistant to enzymatic degradation.

Correct Answer: C

Rationale: The correct answer is C: Methoxamine. Beta receptor agonists stimulate beta receptors, leading to various effects like increased heart rate and bronchodilation. Methoxamine is an alpha-1 adrenergic agonist, not a beta receptor agonist. Epinephrine, Isoproterenol, and Dobutamine are all beta receptor agonists, so they are incorrect choices. Epinephrine acts on both alpha and beta receptors, Isoproterenol is a non-selective beta agonist, and Dobutamine primarily targets beta-1 receptors.

Correct Answer: B

Rationale: The correct answer is B, Reserpine, as it inhibits the storage of norepinephrine and other neurotransmitters in vesicles, indirectly blocking adrenoreceptor activation. Tolazoline (A) is a vasodilator, Carvedilol (C) is a non-selective beta-blocker with alpha-blocking activity, and Prazosin (D) is a selective alpha-1 adrenergic receptor antagonist. Reserpine is the only indirect-acting adrenoreceptor blocking drug among the choices provided.

Correct Answer: A

Rationale: Phenobarbital is the correct answer because it is a known inducer of hepatic drug-metabolizing enzyme systems, such as cytochrome P450 enzymes. This increase in enzyme activity can lead to faster metabolism and clearance of drugs, resulting in potential drug interactions. Zolpidem, Flurazepam, and Zaleplon are not known to significantly increase the activity of hepatic drug-metabolizing enzymes, making them incorrect choices.

Correct Answer: C

Rationale: Rationale: Carbamazepine is the correct answer because it is a first-line treatment for trigeminal neuralgia due to its mechanism of action in inhibiting voltage-gated sodium channels. This helps reduce neuronal firing and alleviate nerve pain. Primidone and Lamotrigine are not typically used for trigeminal neuralgia. Topiramate may have some efficacy, but it is not as effective as Carbamazepine, which is the drug of choice for treating this condition.