Expert: Dr Alan Galbraith - 9/20/2009

Question
QUESTION: I have heard that many dermatologists prescribe the product Clenia, sodium sulfacetamide, to patients with sulfa allergies.  I am wondering what the pharmacologic explanation is for the ability to be able to do this.  Does it have something to do with the fact that it is topical and not systemic?Thanks!

ANSWER: Dear Avnee

Like you say, it is not absorbed when applied topicaly. However, if applied to broken or abraded skin it cause cause an allegic reaction in who is suplha sensitive.

Regards

Dr Alan Galbraith

---------- FOLLOW-UP ----------

QUESTION: Thanks for your reply but I am still confused.  The product information notes that people with sulfa hypersensitivities should not use sodium sulfacetamide.  I am wondering exactly why that is if systemic absorption is rare.  Through some research, I have found that sulfa antibiotics are more likely to cause a reaction than nonantibiotics.  However, sodium sulfacetamide is still an antibiotic so it is still considered in the more reactive group.  Also, what is the difference between a sulfa allergy and a sulfur allergy?  Thanks.

Answer
Dear Avnee

Product information has to be supercautious because of litigation etc so the risks are very often overstated.

I do not quite understand this statement. "Through some research, I have found that sulfa antibiotics are more likely to cause a reaction than nonantibiotics".  ie what are non-antibiotics - to me this a meaningless term and I need clarification on this. Sulphacetamide can
be classified as an antibiotic.

Sulpha allergy pertains to sulpha drugs which include sulphacetamide and many non-antibiotic drugs eg some are used in diabetes. The drugs contain a specific group which has a sulphur atom in it. Sulphur is an element and is rarely used in medicine these days except for example a little in acne treatment. As they are very different chemically speaking cross sensitivities are rare.

Regards

Alan Galbraith