Is a patient allergic to morphine (opioid analgesic) also allergic to oxycodone (opioid analgesic)?

From the Guidelines

A patient allergic to morphine may not necessarily be allergic to oxycodone, but caution is warranted due to potential cross-reactivity. Cross-reactivity between opioid medications is not universal and depends on the specific nature of the allergic reaction 1. True allergic reactions to opioids (involving immune system activation) are relatively rare, while many reported "allergies" are actually adverse effects like nausea, vomiting, or respiratory depression. If a patient has experienced a true allergic reaction to morphine (such as hives, rash, swelling, or anaphylaxis), there is some risk of cross-reactivity with oxycodone, though the risk varies.

Key Considerations

• The chemical structures of different opioids play a role in cross-reactivity patterns.
• Morphine and oxycodone have some structural differences that may allow a patient allergic to one to tolerate the other.
• For patients with documented morphine allergy who require pain management, careful consideration should be given to the severity of the previous reaction. Some key points to consider when deciding on the use of oxycodone in a patient allergic to morphine include:
• The severity of the previous allergic reaction to morphine
• The availability of alternative pain management options
• The need for close medical supervision and monitoring when introducing oxycodone In cases of severe allergic reactions to morphine, it would be prudent to avoid oxycodone and consider non-opioid pain management alternatives, as suggested by the use of oral NSAIDs, oxycodone, and hydromorphone being generally superior to codeine-acetaminophen combinations 1. For milder reactions, oxycodone might be cautiously tried under medical supervision with appropriate monitoring and emergency measures available.

From the Research

Allergic Reactions to Morphine and Oxycodone

• Allergic reactions to opioids are rare, but they can occur with naturally occurring compounds like morphine and codeine 2.
• There is no direct evidence to suggest that a patient allergic to morphine is also allergic to oxycodone, as they are two distinct opioid analgesics with different pharmacological properties 3, 4.
• However, it is essential to note that both morphine and oxycodone are opioid analgesics that work by interacting with the μ-opioid receptor, which may lead to similar side effects and allergic reactions in some individuals 3, 5.

Cross-Reactivity between Morphine and Oxycodone

• There is limited research on the cross-reactivity between morphine and oxycodone, but studies suggest that they have different analgesic potencies and effects on the pain system 4.
• A study found that oxycodone had a greater analgesic effect than morphine in response to skin, muscle, and oesophageal pain stimulation, indicating that they may have different mechanisms of action 4.
• Another study found that oxycodone is a potent μ-agonist and that at least part of its analgesic action is mediated by active metabolites, which may contribute to its distinct pharmacological profile compared to morphine 5.

Clinical Implications

• Clinicians should be aware of the potential for allergic reactions to opioids, including morphine and oxycodone, and take a detailed allergy history before administering these medications 2.
• If a patient is allergic to morphine, it is crucial to exercise caution when administering oxycodone, as there is limited research on cross-reactivity between the two opioids 2.
• Further studies are needed to fully understand the relationship between morphine and oxycodone allergy and to provide guidance on safe administration practices 3, 4, 2, 6, 5.