Which of the following medications would likely cross-react in a patient with a morphine allergy?

• A. Fentanyl
• B. Hydromorphone
• C. Oxycodone
• D. Codeine

Answer: (D)

Patients with a morphine allergy are at risk of cross-reactivity with codeine. This is primarily due to the structural similarity between codeine and morphine, as both belong to the same class of opioids and share similar chemical structures and metabolic pathways.

Codeine is a naturally occurring alkaloid that is derived from morphine and can cause similar allergic reactions in individuals who have a sensitivity to morphine. When a patient is allergic to morphine, their immune response may also recognize codeine as a related compound, potentially triggering the same type of allergic reaction.

In contrast, while fentanyl, hydromorphone, and oxycodone are also opioids, they have different chemical structures that do not resemble morphine as closely as codeine does. Therefore, the likelihood of cross-reactivity with these medications remains low compared to codeine. This distinction explains why codeine is more likely to provoke an allergic reaction in those with a history of morphine allergy.