Tolerance and drug resistance can be a consequence of:

Correct Answer: A

Rationale: The correct answer is A: Change in receptors, loss of them or exhaustion of mediators. Tolerance and drug resistance often occur due to changes in receptors, such as downregulation or desensitization, leading to decreased drug efficacy. Loss of receptors or exhaustion of mediators can also contribute to reduced drug response over time. Explanation of why other choices are incorrect: B: Increased receptor sensitivity would not lead to tolerance or drug resistance, as it would result in enhanced drug effects. C: Decreased metabolic degradation would increase drug levels in the body, potentially leading to increased drug effects rather than tolerance. D: Decreased renal tubular secretion may alter drug excretion but would not directly cause tolerance or drug resistance.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Succinylcholine is a depolarizing agent because it acts as a nicotinic acetylcholine receptor agonist. 2. It causes initial depolarization of the motor end plate leading to muscle fasciculations. 3. By maintaining depolarization, it prevents repolarization and muscle contraction, inducing muscle relaxation. Summary: A. Vecuronium is a non-depolarizing agent that blocks acetylcholine receptors. B. Scopolamine is an anticholinergic drug used for motion sickness. D. Hexamethonium is a ganglionic blocker used for hypertension.

Correct Answer: B

Rationale: The correct answer is B: A decrease in intraocular pressure. Depolarizing blockade, such as with succinylcholine, leads to sustained depolarization of the neuromuscular junction, causing muscle paralysis. This can result in hyperkalemia due to potassium release from muscles, emesis due to stimulation of chemoreceptors, and muscle pain due to fasciculations. Intraocular pressure is not affected by depolarizing blockade. Therefore, a decrease in intraocular pressure is not an effect seen with depolarizing blockade, making choice B the correct answer.

Correct Answer: A

Rationale: Step 1: Identify the key difference between epinephrine and ephedrine - epinephrine is a direct-acting sympathomimetic. Step 2: Ephedrine is a mixed-acting sympathomimetic, acting indirectly by releasing norepinephrine from nerve terminals. Step 3: Therefore, the correct answer is A because ephedrine is not a direct-acting sympathomimetic like epinephrine. Summary: B is incorrect because ephedrine does have oral activity, C is incorrect as ephedrine is not resistant to MAO and has a shorter duration of action, and D is incorrect as ephedrine is less potent than epinephrine.

Correct Answer: A

Rationale: Rationale: Betaxolol is the correct answer as it is a beta1-selective antagonist with a long duration of action due to its lipophilic properties. It has minimal beta2 or intrinsic sympathomimetic activity, leading to prolonged effects on heart rate and blood pressure. Sotalol (B) is a non-selective beta-blocker with class III antiarrhythmic properties. Nadolol (C) is a non-selective beta-blocker with a long duration, but not beta1-selective. Metoprolol (D) is a beta1-selective antagonist but has a shorter duration compared to betaxolol.