Why is it bad to use both topical and oral diphenhydramine?
October 20, 2005 8:04 PM   Subscribe

Why is it bad to use both topical and oral diphenhydramine?

I've wondered this for a long time and can't really figure out how to formulate a Google query that'll get me the answer. The Benadryl website just says "don't do it," same as the products themselves. Does the topical get into the bloodstream somehow and potentially cause an overdose? Are they just covering their asses? Topical diphenhydramine has no side-effects on me--it doesn't seem to get into my bloodstream or if it does it's in such a small amount that it doesn't affect me--whereas oral diphenhydramine makes me sleepy, groggy, etc.

I'm having an allergic reaction to my deodorant that I'd love to get rid of with the topical but I've taken oral diphenhydramine within the past six hours for congestion, and I don't want to apply it in light of that scary vague warning.
posted by Kosh to Health & Fitness (3 answers total)
 
Does the topical get into the bloodstream somehow and potentially cause an overdose?

Yes, according to my doctor. However, I've used both at the same time with no problem. I frequently get hives and rashes; my current strategy is to take claritin hives relief (even if I have a non-hives rash) and use topical benadryl/diphenhydramine. Works great for me. As always, YMMV.
posted by necessitas at 8:16 PM on October 20, 2005


A PubMed search turns up articles like Diphenhydramine toxicity from combined oral and topical use, but their server is down right now so I can't read the abstract.
posted by mbrubeck at 8:18 PM on October 20, 2005


Best answer: This is the FDA ruling that added the wording. That led me to the original FDA proposal, which says:
Since publication of the external analgesic tentative final monograph, the agency has become aware of reports of adverse events (toxic psychosis), especially in children, when diphenhydramine was used topically for relief of pruritus due to chicken pox, poison ivy, and sunburn.
And then lots and lots of details which you should read. FWIW, the final ruling mentions objections that the risk is tiny and not worth adding a warning for:
One comment contended that the proposed label changes for diphenhydramine products are not necessary and would have no significant impact. The comment stated that the 23 reported cases of toxicity between 1979 and 1989 discussed in the proposal (62 FR 45767 at 45768) are minute compared to the millions of applications of these topical products. Further, in all cases, the toxicity was due to consumer noncompliance with directions and indications. In the majority of cases, no treatment was required except for discontinuance of the drug, with affected consumers released from medical care in 24 hours. The comment concluded that additional warnings would have no effect on consumers who have obviously ignored the existing warnings.
(I'm impressed all this stuff is out there and not horribly hard to find.)
posted by smackfu at 8:42 PM on October 20, 2005 [1 favorite]


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