The nurse is reviewing the medication administration record of a patient who is taking isoniazid (INH). Which drug or drug class has a significant drug interaction with isoniazid?

Correct Answer: C

Rationale: The correct answer is C: phenytoin (Dilantin) has a significant drug interaction with isoniazid. Phenytoin is a substrate of the enzyme CYP2C9, which is inhibited by isoniazid, leading to increased phenytoin levels and potential toxicity. Pyridoxine (A) is often given with isoniazid to prevent peripheral neuropathy. Penicillins (B) do not have significant interactions with isoniazid. Benzodiazepines (D) are not metabolized through CYP2C9 and therefore do not interact significantly with isoniazid.

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: B

Rationale: The correct answer is B because carbachol causes miosis (pupillary constriction) instead of mydriasis (pupillary dilation). Carbachol stimulates muscarinic receptors causing constriction of the pupil. Choices A, C, and D are incorrect because carbachol does decrease intraocular pressure, exerts both nicotinic and muscarinic effects, and is resistant to acetylcholinesterase, respectively.

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.