Correct Answer: A

Rationale: The correct answer is bradycardia. Diltiazem, a calcium channel blocker, can lead to bradycardia as a side effect. Bradycardia should be reported immediately because it can result in serious cardiac complications, especially in a client with atrial fibrillation.

Correct Answer: A

Rationale: Visual disturbances, such as blurred or yellow vision, can be an early sign of digoxin toxicity. Monitoring for visual changes is crucial to detect and prevent potential adverse effects of digoxin.

Correct Answer: C

Rationale: Ondansetron can cause tremors as an adverse effect. Monitoring for tremors is essential as it can indicate a potential adverse reaction to the medication and prompt intervention is necessary to ensure the client's safety and comfort.

Correct Answer: D

Rationale: A therapeutic response to levothyroxine is indicated by a decrease in the level of TSH. This decrease signifies that the body requires less stimulation to produce thyroid hormone, reflecting a normalization of thyroid function due to the medication's effectiveness.

Correct Answer: C

Rationale: Penicillin is classified as an antibacterial drug, specifically used to treat bacterial infections. It works by inhibiting the growth of bacteria, making it an effective treatment for various bacterial infections.