This is based on a 2014 report on Pharmacist's Letter titled "Sulfa drugs and the sulfa-allergic patient." This list will disclose what the labeling says and what the evidence is. Unfortunately, the product labeling of many nonantibiotic sulfonamide agents does not correlate with what is known scientifically. For instance, many diuretics are either contraindicated or contain warnings regarding their use in patients with a history of sulfonamide allergy (see table).1,2 The inconsistency between product labeling and available evidence is likely because some of these agents (e.g., hydrochlorothiazide) were marketed many years before these newer theories refuting cross-reactivity were developed.
The inconsistency between product labeling and scientific evidence places clinicians in a difficult position. The routine avoidance of sulfonamide-containing drugs in patients with a history of sulfa allergy can unnecessarily complicate or compromise patient care. However, to ignore the product labeling recommendations places clinicians at risk of liability.
In a 2019 article, it was determined that "sulfa" drugs can be divided into two types: microbial and non-microbial, with the non-microbial lacking the functional groups necessary to generate a large immunologic response. Basically, if the name starts with "sulfa", then it's a microbial sulfa that actually contains the functional group that makes people allergic.
In a retrospective study assessed within that same article, it was found that, if a patient was prescribed a microbial sulfa and then later prescribed a non-microbial sulfa, then those with a sulfa allergy to the former have a 10x higher risk of being allergic to the non-microbial sulfa (e.g. 9.9% vs 1.6%). However, sulfa-allergic patients had a likewise correspondingly higher risk of a penicillin allergy, implying that these patients simply have a propensity for allergies in general rather than a specific sulfa allergy to the non-microbials. So, cross-allergies are quite possible but absolutely not guaranteed. And, if a patient is likely to be allergic to possibly anything, then, in the interest of them being on ANY therapy, it would be prudent to test their tolerances. (first citation contains great chart for likelihood of cross-allergy)