When giving dextromethorphan, the nurse understands that this drug suppresses the cough reflex by which mechanism of action?

Correct Answer: C

Rationale: The correct answer is C because dextromethorphan suppresses the cough reflex by directly acting on the cough center in the brain. This drug inhibits the signals that trigger the cough reflex, leading to reduced coughing. Choice A is incorrect as dextromethorphan does not depress the central nervous system like opioids. Choice B is incorrect because dextromethorphan does not anesthetize stretch receptors. Choice D is incorrect as dextromethorphan does not affect the viscosity of bronchial secretions.

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: Procaine. It is a short-acting drug due to its rapid metabolism by plasma esterases, resulting in a shorter duration of action compared to the other choices. Procaine's quick onset and short duration make it suitable for minor procedures. Tetracaine, Bupivacaine, and Ropivacaine are all long-acting local anesthetics with slower metabolism and longer durations of action, making them more suitable for prolonged surgeries or chronic pain management.

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.