Keywords: opioid, opiate, allergy, hypersensitivity (PubMed Search)
How many times have you had a patient with an allergy to codeine described as stomach upset? Or how about a rash with morphine (probably secondary to histamine release)? True anaphylactic reactions to opioids are very rare (< 1%). But what happens when you have a patient with a true allergy, but still need to give an opioid? No problem, you just need to choose one that is structurally different.
All of the group 1 and 2 agents are structurally very similar to each other and should not be given if a true allergy exists to any other natural or semi-synthetic derivative. Group 3 agents have structures different enough that they can be given to a patient intolerant to the natural or semi-synthetics without fear of cross reactivity. They are also very different from others in this same group.