This updated Medicines Q&A evaluates the limited evidence available on cross-sensitivity between sulfonamide-containing medicines and lists classes of medication that contain a sulfonamide in their chemical structure.


The summary is as follows:


Patients with documented allergy to sulfonamide antibiotics may be at increased risk of all drug-induced reactions that appear to be allergic in nature, irrespective of drug class. The term “sulfa-allergy” is misleading, restrictive, and should be avoided. Healthcare professionals should instead document the exact drug and the nature of the reaction as they would an adverse reaction to any other drug.


The existence of a cross-sensitivity between sulfonamide antibiotics and sulfonamide non-antibiotics is not supported by theory or clinical data (with the exception of sulfasalazine). Many experts do not agree with the contraindication of drugs simply on the basis of their chemical structure, but a large number of manufacturers still contraindicate the use of their drugs in patients with a documented hypersensitivity to sulfonamides.


Prescribers should be aware that this is a subject on which there is extreme variability, even in advice given for the same drug. Where a non-sulfonamide containing option is available, it would be prudent for prescribers to consider this before a sulfonamide-containing alternative.


In cases where it would be detrimental to the patient’s health to avoid using a particular therapy, consideration should be given to using one of the drugs listed above. Clinicians should conduct a careful risk-benefit assessment before prescribing, taking into account the history and nature of the allergy and any other drugs the patient may have taken, as it is possible they will have taken another sulfonamide in the interim period without it being realised. Patients will need to be counselled and monitored. Any decision to prescribe needs to be in the knowledge that if use of a drug is contraindicated, the prescriber is taking responsibility.


For patients with a convincing history of significant sulfonamide hypersensitivity reaction, for whom no acceptable alternative medications exist, desensitisation procedures may be attempted, in an environment where appropriate monitoring can be carried out.