Solving the confusion between sulfa, sulfate and sulfites

One Saturday morning, 55-year-old Sara stalked up to our pharmacy counter, a brown prescription vial in her hand and a look that could blister paint on a wall 10 feet away. “I can’t take this stuff, it has Sulfa in it, it says so right on the label! I’ve told you, I’m deathly allergic to sulfa. I could have died!”
“Sara, you’re not in any danger. See? This medicine is a sulf-ATE, not a sul-FA. They sound quite similar, but don’t worry, they’re not the same thing at all.
This medicine contains a sulfate, which means that part of it contains a salt that has some sulfur in it. The salt part isn’t an active part of the medicine; it’s just the way it’s made. Even people who are allergic to sulfa drugs can take medicines like this without any trouble.
I can’t guarantee that you won’t have a reaction to this medicine, Sara, but if you do, it will be the OTHER part of your medicine that’ll be the trouble, not the salt part of it.”
When someone reports they are allergic to sulfa, it usually means that they’ve had an allergic reaction to an antibiotic containing sulfa. Sulfa-containing antibiotics are called sulfonamides because they contain a specific cluster of sulfur, oxygen, nitrogen and hydrogen molecules called a sulfonamide moiety. It’s the shape of that entire cluster that triggers the reaction, not the fact that it contains sulfur.
There are three general types of these sulfonamide compounds, each with a different chemical structure. Sulfa antibiotics make up one type of them.
People with a true allergy to sulfonamide antibiotics don’t have to avoid the other 2 groups of sulfonamide compounds because cross-reactivity between the different groups is not very common.  
It’s true that people allergic to sulfonamide antibiotics are more likely to experience allergic reactions to other types of sulfonamide medicines, but that’s only because they also tend to react more often to different medicines and chemicals like in soaps and foods, not because of any direct cross-sensitivity or cross-reaction with the other sulfonamides.
Only about 3% of the general population has a true allergy to “sulfa drugs”, or sulfonamide antibiotics. If you are one of them, you should definitely avoid the sulfa antibiotic sulfamethoxazole and anything that contains it, like the antibiotic combination trimethoprim-sulfamethoxazole. With 11 syllables to pronounce and spell, trimethoprim-sulfamethoxazole is often referred to by its older brand names Bactrim®, Septra® or abbreviated as TMP-SMX or SMX-TMP.
People experiencing an allergic reaction to a sulfonamide antibiotic often notice a red, raised itchy rash. The rash can progress into a serious, even life-threatening reaction affecting deeper layers of the skin and affecting other organs. Anyone who has had a severe or life-threatening reaction to any medication, not just sulfamethoxazole, should always let their doctor and pharmacist know, because people who have experienced a serious allergic reaction to one medicine are more likely to react to others.
Another type of reaction that is confused with an allergic reaction to sulfa is sensitivity to sulfites, which can cause trouble breathing in sensitive people. Sulfites are preservatives used in foods, wines and some medicines like eye drops. Sulfites were once widely used on fruits and vegetables to combat bacteria, but are now restricted. The Food and Drug Administration (FDA) requires any foods, wines or medicines containing sulfites to disclose it on the label.
Here are 4 Key Facts About Taking Sulfa Drugs, Sulfates and Sulfites:
1. Sulfates and sulfites are chemically different from sulfa drugs.
Being allergic to sulfa antibiotics doesn’t mean that you will react to sulfates or sulfites.  
2. Sulfa antibiotics have several different names.
Trimethoprim-sulfamethoxazole is the sulfa antibiotic most used in the United States, a name too long to say easily or fit onto a prescription label. Watch out for the names Bactrim®, Septra®, co-trimoxazole and the abbreviations TMP-SMX or SMX-TMP.
3 .If you develop a rash, call your doctor right away.
Sulfa antibiotics can trigger a rash that can turn into a life-threatening allergic reaction called Stevens-Johnson syndrome. Stevens-Johnson starts out as a full-body rash, can eventually cause your skin to peel completely off, and progress to organ failure and even death.  
4. If you have asthma, avoid sulfite preservatives.
People with asthma are more likely to react to sulfites, which are preservatives commonly found in foods, wines and in some eye drops. The FDA requires foods or medicines preserved with sulfites to show that on their labeling, to allow you to avoid them more easily.

Dr. Louise Achey, Doctor of Pharmacy is a 40-year veteran of pharmacology and author of Why Dogs Can’t Eat Chocolate: How Medicines Work and How YOU Can Take Them Safely. Check out her NEW website TheMedicationInsider.com for daily tips on how to take your medicine safely. 2020 Louise Achey