The charge nurse asks the practical nurse (PN) to administer diphenhydramine 25 mg IM to a client prior to infusing a blood transfusion. Which explanation should the PN offer the client about the purpose of this drug?

Choice A reason: Taking a benzodiazepine with morphine is incorrect, as it increases sedation and respiratory depression risk, a dangerous opioid side effect. This indicates misunderstanding, as morphine’s primary management focuses on pain and side effects like constipation, not concurrent sedative use.

Choice B reason: Observing bowel movements and using a stool softener shows understanding, as morphine causes constipation by slowing gastrointestinal motility via opioid receptors. Proactive management with stool softeners prevents complications like impaction, aligning with safe opioid use in cancer pain management.

Choice C reason: Grapefruit juice avoidance is irrelevant to morphine, as it affects drugs metabolized by CYP3A4, not opioids. Morphine is metabolized via glucuronidation, unaffected by grapefruit. This indicates misunderstanding, as it does not address morphine’s key side effects or management.

Choice D reason: Watching for agitation or insomnia is not a primary concern with morphine, which causes sedation. These symptoms may relate to other conditions, but they do not reflect understanding of morphine’s effects, like constipation, making this choice incorrect.

Choice A reason: Cephalexin, a cephalosporin, has a 5–10% cross-reactivity risk with penicillin allergies due to similar beta-lactam structures. An anaphylactic history increases the risk of severe reactions. Contacting the provider ensures safety, potentially leading to an alternative antibiotic to prevent life-threatening allergic responses.

Choice B reason: Monitoring for rash or hives is reactive and insufficient for a client with a penicillin anaphylaxis history. Cephalexin’s cross-reactivity risk requires proactive avoidance, not just observation, as anaphylaxis can occur rapidly, making this choice inadequate compared to provider consultation.

Choice C reason: Giving cephalexin with an antihistamine does not prevent anaphylaxis, which can be rapid and severe in penicillin-allergic clients. Antihistamines mitigate mild allergies but are ineffective against severe reactions. This choice is unsafe without confirming the drug’s appropriateness first.

Choice D reason: Administering cephalexin as prescribed ignores the significant risk of cross-reactivity with penicillin, given the client’s anaphylactic history. This could trigger a life-threatening reaction, as cephalosporins share structural similarities with penicillins, making immediate administration without verification dangerous.