All of the following statements about efficacy and potency are true EXCEPT:

Correct Answer: D

Rationale: The correct answer is D because the ED50 is a measure of potency, not efficacy. Efficacy refers to the maximum effect of a drug, while potency is the comparative measure of the doses needed to produce the same effect. Therefore, A is incorrect because efficacy can be more important clinically than potency in certain situations. B is true as efficacy is indeed the maximum effect of a drug. C is also correct as it accurately describes potency as a comparative measure. In summary, D is incorrect because the ED50 is a measure of potency, not efficacy, making it the exception among the statements provided.

Correct Answer: A

Rationale: The correct answer is A: Hypotension and bradycardia. Nicotine is a stimulant that typically causes hypertension and tachycardia due to its effects on the sympathetic nervous system. Therefore, hypotension and bradycardia are not consistent with the toxic effects of nicotine. Choices B, C, and D are incorrect because convulsions, coma, respiratory arrest, skeletal muscle depolarization blockade, respiratory paralysis, hypertension, and cardiac arrhythmias are all potential toxic effects of a large dose of nicotine due to its impact on various physiological systems.

Correct Answer: D

Rationale: The correct answer is D (Both B and C). Succinylcholine and mivacurium are metabolized by plasma cholinesterase. An abnormal variant of plasma cholinesterase (B) can lead to prolonged neuromuscular blockade. Additionally, hepatic disease (C) can impair the metabolism of these drugs, further prolonging their effects. Therefore, in patients with both abnormal plasma cholinesterase and hepatic disease, the neuromuscular blockade can be significantly prolonged. Renal failure (A) does not directly impact the metabolism of succinylcholine and mivacurium, so it is not a significant factor in this context.

Correct Answer: A

Rationale: The correct answer is A: Xylometazoline. Xylometazoline is an alpha2-selective agonist, which means it specifically targets alpha2-adrenergic receptors. By activating these receptors, xylometazoline promotes constriction of the nasal mucosa, leading to reduced swelling and congestion. Phenylephrine (B) and methoxamine (C) are alpha1-selective agonists, not alpha2-selective, so they would not promote constriction of nasal mucosa. Epinephrine (D) is a non-selective agonist that acts on both alpha and beta receptors, leading to a broader range of effects, not specifically nasal constriction.

Correct Answer: A

Rationale: The correct answer is A because beta-blocking agents do not affect plasma lipid levels directly. Beta-blockers can decrease HDL levels and increase VLDL levels, which is opposite to choice A. Bronchoconstriction (B) is a common side effect of non-selective beta-blockers due to their action on beta-2 receptors in the lungs. Decrease in aqueous humor production (C) is a therapeutic effect of beta-blockers in treating glaucoma. "Membrane-stabilizing" action (D) refers to the ability of some beta-blockers to block sodium channels in the cardiac muscle, leading to antiarrhythmic effects.