Tolerance develops because of:

Correct Answer: C

Rationale: Tolerance develops due to the body adapting to a drug's presence, requiring higher doses for the same effect. Diminished absorption means less drug enters the body, leading to tolerance. Rapid excretion removes the drug quickly, causing the body to adjust, also leading to tolerance. Therefore, both factors contribute to tolerance development. Choice C is correct. Choices A and B alone do not fully explain tolerance development as they are only partial explanations, making them incorrect.

Correct Answer: A

Rationale: The correct answer is A: Pancuronium. It is a nondepolarizing muscle relaxant that works by blocking acetylcholine receptors at the neuromuscular junction, leading to muscle relaxation. Succinylcholine (B) is a depolarizing muscle relaxant that causes initial muscle depolarization before relaxation. Hexamethonium (C) is a ganglionic blocking agent used for hypertension. Scopolamine (D) is an anticholinergic drug used for motion sickness. Thus, the correct choice is A as it specifically acts as a nondepolarizing muscle relaxant by blocking acetylcholine receptors.

Correct Answer: B

Rationale: The correct answer is B: Succinylcholine. Succinylcholine can increase intraocular pressure, which is dangerous for patients with glaucoma. This is due to its depolarizing mechanism of action, causing muscle fasciculations and potential pressure build-up in the eye. A: Tubocurarine is a nondepolarizing neuromuscular blocking agent and not contraindicated in glaucoma. C: Pancuronium is a nondepolarizing agent and does not have a significant effect on intraocular pressure. D: Gallamine is a nondepolarizing agent and is not contraindicated in glaucoma.

Correct Answer: C

Rationale: Rationale: Ephedrine is preferable for chronic orthostatic hypotension because it acts as a sympathomimetic by increasing both norepinephrine and epinephrine release, thus improving blood pressure regulation over time. Epinephrine (A) has a short duration of action and may lead to tachycardia. Norepinephrine (B) primarily acts on alpha receptors, which may cause vasoconstriction and worsen orthostatic hypotension. Salmeterol (D) is a long-acting beta-2 agonist used in asthma, not suitable for orthostatic hypotension.

Correct Answer: C

Rationale: The correct answer is C: Sotalol. Sotalol is a nonselective beta-blocker with no intrinsic sympathomimetic or local anesthetic activity, making it suitable for treating life-threatening ventricular arrhythmias. Propranolol (A) is also a nonselective beta-blocker but has intrinsic sympathomimetic activity. Oxprenolol (B) is nonselective but has partial agonist activity. Atenolol (D) is a selective beta-1 blocker and not suitable for ventricular arrhythmias.