Question:

Can someone with an allergy to bactrim safely take glyburide or glipizide without having to worry about developing an allergic reaction? If not, can he/she try one of the newer sulfonlyureas released in the last year or two?

Answer:

The question raised is one that arises frequently in the abstract but infrequently (for me) in real life. The concern is that because the sulfonylurea drugs are similar in structure to sulfa antibiotics, there could be an important risk of an allergic cross-reaction when the sulfonylurea drug is given to the sulfa-allergic person?

There is no mention of sulfa cross-reactive allergy in the package insert for the original brands of glipizide or glyburide to guide us in one way or another. I asked this question of an allergy specialist many years ago who told me that in practice they never see patients where this proves to be the case. Are there valid studies that can allow an evidence-based decision? I`m afraid not. Within those constraints then, we face coming to some practical answer. If I have a patient who had a life-threatening reaction to a sulfa in the past, I would be more cautious than I would with a person who had an annoying but non-dangerous reaction. If I had alternative forms of therapy which were indicated in the individual patient, I would be inclined to avoid the ambiguous situation raised by using the drug with the small chance of an allergic reaction by using the alternative. If I felt on balance that the risk associated with the small potential for an allergic reaction were preferable to the risk of the alternate therapy, I would consider the potential risk of using the sulfonylurea worth taking. I think the risk of the cross allergy is small but I cannot say that it is zero.

There are several drugs which act through the same receptor as the sulfonylurea drugs but differ in structure. The concerns about cross allergy would not apply to these drugs. One such drug, called repaglinide, is approved by the Food and Drug Administration and is available in the United States. Another, called nateglinide, is under development but as far as I know it has not been decided upon by the Food and Drug Administration for the United States and is not available here.

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