A patient who has heart failure. The patient complains of shortness of breath, and the nurse auscultates crackles in the lungs. The nurse understands that these symptoms are the result of

Choice A reason: Morphine, an opioid, binds to mu, kappa, and delta receptors in the brain, spinal cord, and gastrointestinal tract. Mu receptors in the gut slow peristalsis, causing constipation, while central receptors relieve pain. This multi-receptor binding explains both therapeutic and side effects, making this the correct choice.

Choice B reason: Constipation from morphine occurs at therapeutic, not just toxic, doses due to mu receptor activation in the gastrointestinal tract, which reduces motility. Toxicity may worsen side effects, but constipation is a common effect at standard doses, making this choice inaccurate for explaining morphine’s mechanism.

Choice C reason: Morphine’s receptors (e.g., mu) regulate multiple processes, but the drug itself isn’t selective to multifunctional receptors. It binds broadly to opioid receptors, causing both analgesia and side effects like constipation. This choice misrepresents morphine’s non-selective binding, making it less accurate than choice A.

Choice D reason: Morphine’s effects, including analgesia and constipation, result from specific receptor binding, not coincidental processes. It activates opioid receptors in the brain for pain relief and in the gut for reduced motility. This choice incorrectly suggests constipation is unrelated to morphine’s pharmacological action, making it incorrect.

Choice A reason: Questioning why allergies aren’t aren’t in the chart is secondary and confrontational. Clarifying the specific allergy ensures safety, so this is incorrect for the first action.

Choice B reason: Identifying the specific antibiotic and reaction verifies the allergy, preventing anaphylaxis or harm. This is the priority safety step, making it the correct first action.

Choice C reason: Lowering the dose doesn’t address the allergy risk; allergic reactions can occur regardless. Verifying the allergy is critical first, so this is incorrect.

Choice D reason: An antihistamine may mitigate mild reactions but doesn’t confirm the allergy. Clarifying the allergy prevents unsafe administration, so this is incorrect for the first step.