"sulfa" as in the antibiotics? This refers to a "sulfonamide" moiety in chemical structure:
The classic example of a "sulfa" antibiotic is:
Sulfanilamide:can you spot the sulfonamide function within that structure?
It's at the right.
Allergy to so-called "Sulfa/Sulpha" drugs is completely real, completely well-recognized, and has been relatively common for the past fifty years or so, since the drug class become widely used after WWII.
it is not
related to allergy (or anaphylactoid intolerance, perhaps more correctly stated) to SULFITES.
Sulfite, on the other hand, is a simple inorganic anion (that is, it is negatively charged):
Sulfites are used as a food preservative or enhancer. They also occur in nature.
They may come in several related forms, such as--
Sulfur dioxide, (not a sulfite, but a closely related chemical oxide that can
, in solution, be interconverted to sulfite)
Potassium bisulfite or potassium metabisulfite
Sodium bisulfite, sodium metabisulfite or sodium sulfite
Sulfa drugs work because they impair a particular enzymatic pathway in bacteria. Well, in non-resistant bacteria, anyway.
In bacteria, antibacterial sulfonamides act as competitive inhibitors of the enzyme dihydropteroate synthetase (DHPS), an enzyme involved in folate synthesis. Sulfonamides are therefore bacteriostatic and inhibit growth and multiplication of bacteria, but do not kill them. Humans, in contrast to bacteria, acquire folate (vitamin B9) through the diet.
Sulfite sensitivity is slightly more common in those with salicylate sensitivity-- many asthmatics already know if they have such a sensitivity. It can also occur as a result of a particular genetically caused metabolic disorder which is usually fatal in early childhood.Any questions?