Which one of the following groups is responsible for the duration of the local anesthetic action?

Correct Answer: A

Rationale: The correct answer is A: Intermediate chain. The duration of local anesthetic action is mainly determined by the intermediate chain in the structure. The length and structure of the intermediate chain influence the rate of diffusion through tissues and the binding affinity to sodium channels. Lipophilic and ionizable groups do play a role in the mechanism of action of local anesthetics but do not directly affect the duration of action. Therefore, choice A is the most relevant in determining the duration of local anesthetic action compared to the other choices.

Correct Answer: A

Rationale: The correct answer is A: Benztropine. Benztropine is an anticholinergic drug that helps improve symptoms of Parkinson's disease by blocking excess acetylcholine in the brain, thus restoring a balance between dopamine and acetylcholine. This helps alleviate tremors, muscle stiffness, and other motor symptoms associated with Parkinson's. Summary of other choices: B: Edrophonium is a reversible acetylcholinesterase inhibitor used for diagnosing myasthenia gravis. C: Succinylcholine is a depolarizing neuromuscular blocker used for muscle relaxation during surgeries. D: Hexamethonium is a ganglionic blocker used to lower blood pressure.

Correct Answer: C

Rationale: The correct answer is C because a relatively pure alpha agonist primarily acts on alpha receptors in blood vessels causing vasoconstriction, leading to increased peripheral arterial resistance and reflex bradycardia. This results in an increase in blood pressure and venous return. Since alpha agonists primarily target blood vessels, they do not have a direct effect on blood vessels. Choices A, B, and D are incorrect as they are known effects of alpha agonists.

Correct Answer: B

Rationale: The correct answer is B: Metoprolol. Metoprolol is a beta1-selective antagonist, meaning it selectively blocks beta1-adrenergic receptors. This specificity results in decreased heart rate and contractility without affecting beta2 receptors, which are primarily found in the lungs. Choice A, Propranolol, is a non-selective beta blocker that blocks both beta1 and beta2 receptors. Choice C, Carvedilol, is a non-selective beta blocker with additional alpha-blocking activity. Choice D, Sotalol, is a non-selective beta blocker with Class III antiarrhythmic properties. Therefore, the correct answer is B as it is the only beta1-selective antagonist among the options provided.

Correct Answer: C

Rationale: Thiopental is the correct answer because it is an ultra-short-acting barbiturate with a rapid onset and short duration of action. It is commonly used for induction of anesthesia due to its fast-acting properties. Secobarbital and Amobarbital are short to intermediate-acting barbiturates, while Phenobarbital is a long-acting barbiturate used for seizure control. In summary, Thiopental stands out as the ultra-short-acting option compared to the other choices due to its specific pharmacokinetic profile.