Usually when one says a sulfa allergy they are referring to sulfonamides,
and most folks
allergic to a sulfonamide antibiotic are still not allergic to sulfa
containing drugs like
lasix, hydrochlorothiazide, or captopril for that matter.  The human body
has many
sulfhydryl groups in many substances produced.  There are folks that do have
a
pan-sulfa allergy and may react to many sulfur containing compounds.  Some
are
allergic to sulfites, but one is more likely to see a pan-sulfa allergy in a
patient with
SLE.     There also may be a cross reactivity in some patients with paba
allergy.