Sunday, May 30, 2010

Truth behind "Sulphur allergy"

Skin rash reactions and very rarely life-threatening Stevens-Johnson syndrome and toxic epidermal necrolysis can be associated with sulphonamides allergy. The chemical structure that is primarily responsible for allergy is the arylamines group present in those antibiotics and not the sulfur moiety per say. FYI, sulfur is a chemical element that is found in many substances even in our body.

As quoted in the article - 'Sulfur allergy' label is misleading, there is insufficient evidence to show allergic cross-reactivity between sulfonamide antibiotics and other sulfonamide drugs such as frusemide and gliclazide. In patients who have had an allergic reaction to one drug, allergic reactions to other drugs, even if entirely unrelated, occur more commonly. For those patients who are allergic to bactrim (sulfamethoxazole / trimethoprim), there is the possiblity of allergy to trimethoprim instead of sulfamethoxazole and therefore avoid BOTH sulfamethoxazole and trimethoprim.

Many patients believe that having been labelled 'sulfur allergic' they are also at risk of adverse reactions or allergies from sulfites, sulfates and even elemental sulfur and may attempt to avoid them. Sulfates are sometimes mildly irritant and sulfites can cause respiratory reactions in patients with asthma and, rarely, non-immunoglobulin E-mediated anaphylactic reactions, but there is no relationship between these reactions and hypersensitivity to sulfonamides. Patients who have had allergic reactions to sulfonamide drugs do not need to avoid sulfites, sulfates or sulfur. The author concluded that allergies should not be attributed to classes or groups of drugs unless proven because assumptions about cross-reactivity may later be found to be incorrect.

In the second article, it is mentioned that a sulfite reaction is different from a sulfonamide allergy (a reaction to sulfa drugs) because sulfites and sulfonamides are entirely different chemicals and have unrelated mechanisms of reaction. Sulfites are commonly present in food preservatives. A person sensitive to sulfites is no more likely to be allergic to sulfonamides than any other individual and vice versa. People allergic to sulphonamide drugs are also unlikely to be allergic to glucosamine.

Adapted from article 2:
Sulfonamide drug classes/individual drugs that may cause allergic reactions
Sulfonamide Antibiotics
Thiazide Diuretics
Loop Diuretics
Carbonic Anhydrase Inhibitors

Other medicines [article4]:

Celebrex®. Celecoxib (Celebrex®), a popular COX-2 inhibitor used for the treatment of arthritis and pain control, is a sulfonamide non-antibiotic medication. Although there have been no reports of sulfa-allergic patients reacting to Celebrex®, it is a theoretical concern, so the recommendation is that sulfa-allergic patients avoid this medication.

Zonisamide. Zonisamide is a sulfonamide medication used for the treatment of seizures. It has been associated with severe skin reactions, those typically seen with sulfa reactions. This medication should not be used in sulfa-allergic patients.

  • Avoid the term 'sulfur allergy'
  • Best to record drugs that the patient is allergic to and nature of the allergic reaction
  • Recommended for sulfa-allergic person to take the first dose of a sulfa-based diuretic under direct medical supervision to be on the safe side

"Sulfa-allergy" label is misleading
What medications should sulfa-allergic patients avoid?

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