Will a patient allergic to morphine (opioid analgesic) experience a reaction to oxycodone (opioid analgesic)?

From the Guidelines

A patient allergic to morphine may still have a reaction to oxycodone, but the likelihood depends on the nature of the allergy and the individual's sensitivity to different opioids. According to the World Health Organization guidelines for cancer pain, patients who have poor analgesic efficacy or tolerability with one opioid may frequently tolerate another opioid 1. However, this does not necessarily mean that a patient allergic to morphine will not react to oxycodone.

Key Considerations

• True allergies to opioids are relatively rare, and what many patients report as "morphine allergies" are often side effects like nausea, itching, or respiratory depression rather than true allergic reactions.
• If a patient has experienced a genuine allergic reaction to morphine, there is a possibility of cross-reactivity with other opioids, including oxycodone.
• The conversion ratio between opioids remains unpredictable, and morphine, oxycodone, and hydromorphone have different chemical structures 1.

Recommendations

• For patients with confirmed morphine allergies, it's recommended to proceed with caution when considering oxycodone.
• If oxycodone is deemed necessary, starting with a low dose under medical supervision is advisable.
• Alternative pain management options, such as non-opioid analgesics (acetaminophen, NSAIDs) or opioids from different chemical classes (like fentanyl or tramadol), might be safer choices for patients with true morphine allergies.
• Always document the specific nature of any previous "allergic" reactions to help distinguish between true allergies and common opioid side effects.

Opioid Rotation

• Opioid rotation, including the use of oxycodone, hydromorphone, and methadone, can be useful in managing patients who are highly tolerant to previously used opioids or experiencing adverse effects 1.
• By substituting opioids and using lower doses than expected, it is possible to reduce or relieve the symptoms of opioid toxicity and improve analgesia.

From the Research

Opioid Allergy and Cross-Reactivity

• Opioid allergy labels are often unsubstantiated in clinical practice, and the removal of erroneous labels is important for pain management 2.
• A study found that patients with documented allergy or adverse drug reaction to opioids had a 100% re-exposure tolerance rate to subsequent opioid exposure, with no cross-reactivity among opioid classes 3.
• Another study found that the risk of IgE-mediated reactions caused by opioids is low in patients with historical IgE-mediated reactions to opioids, and opioid allergy documentations may propagate alert fatigue and unwarranted prescribing changes 4.

Morphine and Oxycodone Cross-Reactivity

• There is limited literature on cross-reactivity among opioid classes, but a study found no cross-reactivity among natural, semisynthetic, and synthetic opioids 3.
• Oxycodone is a semisynthetic opioid, and morphine is a natural opioid, but there is no direct evidence on cross-reactivity between the two 5.
• However, a study suggests that the incidence of allergic cross-reactivity between clinical and chemical opioid classes is low, with cross-reactivity rates ranging from 0% to 6.7% 4.

Clinical Implications

• The diagnosis of opioid allergy and distinction between anaphylactoid and true anaphylactic reactions can be challenging due to uncertainties associated with skin testing and the unavailability of opioid-specific immunoglobulin E antibody tests 6.
• Clinicians should be aware of the low likelihood of true reactivity and the potential for opioid allergy labels to propagate alert fatigue and unwarranted prescribing changes 2, 4.
• Further characterization of opioid allergy labels and evaluation of basophil activation testing in opiate allergy are needed to improve diagnosis and management of opioid allergies 2.