A patient is to receive local anesthesia for removal of a lymph node from his armpit. The physician asks for a solution of premixed lidocaine and epinephrine. The nurse knows that the epinephrine is used for which reason?

Correct Answer: D

Rationale: The correct answer is D because epinephrine is added to lidocaine to vasoconstrict blood vessels, keeping the anesthetic at its local site of action and decreasing incisional bleeding. This helps prolong the duration of anesthesia and reduces the risk of systemic toxicity. A: Incorrect. Epinephrine does not prevent an anaphylactic reaction; it is added for vasoconstrictive effects. B: Incorrect. The anesthetic does not enhance the effect of epinephrine. They have separate roles. C: Incorrect. Epinephrine does not contribute to a balanced anesthetic state; it primarily acts on blood vessels.

Correct Answer: C

Rationale: The correct answer is C: Preventing thrombus formation. Anticoagulant therapy works by inhibiting the formation of blood clots, preventing thrombus formation. This is crucial in conditions like atrial fibrillation or deep vein thrombosis to reduce the risk of clot formation and subsequent embolism. Stabilizing an existing thrombus (A) or dissolving it (B) are typically managed with other medications like antiplatelet or thrombolytic agents. Dilating the vessel around a clot (D) is not the primary goal of anticoagulant therapy.

Correct Answer: D

Rationale: The correct answer is D, Hepatic impairment. Antitubercular drugs are primarily metabolized by the liver, so hepatic impairment can affect drug metabolism, leading to toxicity or reduced efficacy. Glaucoma (A), anemia (B), and heart failure (C) are not direct contraindications to antitubercular therapy. Glaucoma does not affect drug metabolism, anemia does not interfere with drug efficacy, and heart failure does not directly impact antitubercular drugs' effectiveness.

Correct Answer: A

Rationale: The correct answer is A: Faster urinary excretion. Biotransformation involves converting a drug into metabolites that are more easily excreted by the body, primarily through urine. This process increases the water solubility of the drug, allowing it to be eliminated more efficiently. Option B is incorrect because biotransformation typically leads to faster, not slower, urinary excretion. Option C is incorrect as biotransformation does not affect distribution within the organism. Option D is incorrect because biotransformation does not directly impact the binding of the drug to membranes.

Correct Answer: A

Rationale: The correct answer is A because the therapeutic index (TI) is a ratio that measures the safety of a drug by comparing the dose that produces therapeutic effects to the dose that causes toxicity. This ratio helps determine the margin of safety of a drug for a specific indication. Choice B is incorrect because TI does not directly measure effectiveness. Choice C is incorrect as bioavailability is a different concept related to drug absorption. Choice D is incorrect because TI focuses on safety and not drug elimination. Therefore, A is the correct answer as it accurately reflects the purpose of the therapeutic index.