Answer:
Table 4 on page S18 of the practice parameter on allergy testing provides a general recommendation on treatments that affect skin testing (1). The Karaz et al paper is cited as providing evidence that topical doxepin affects skin test reactivity for up to 11 days (2). There is minimal systemic absorption, plasma levels with topical therapy are 0 to 47 ng/ml vs 30 to 150 ng/ml following oral administration (3). However, the suppression was noted on the nonexposed arm, indicating that systemic absorption is likely responsible for the effect. These data are based upon testing of 5 normal individuals. I could not find any reports of the duration of diphenhydramine topical applications, but it would be much shorter in light of the relatively short half-life of diphenhydramine. A topical anesthetic, EMLA™, can be used for itch and should not affect the histamine cutaneous response. Finally, prolonged topical application of corticosteroid creams or ointments may affect allergy testing due to depletion of cutaneous mast cells (4,5,6).
In summary, discontinuation of short-lived antihistamine creams such as diphenhydramine should be stopped 24 hours before testing, long acting H1 inhibitor creams such as doxepin should be discontinued for 11-14 days, topical anesthetics for itch could probably be used up to 8-12 hours before testing and prolonged topical corticosteroid may have a prolonged effect based upon duration and potency of treatment.
1. Bernstein IL, Li JT, Bernstein JI, Hamilton R et al. Allergy diagnostic testing: an updated practice parameter.
Ann Allergy Asthma Immunol 2008;100(S3): S1-148.
2. Karaz, Sameh S., et al. "Effect of topical doxepin cream on skin testing."
Journal of allergy and clinical immunology 96.6 (1995): 997-998.
3.
GenDerm. Zonalon cream (doxepin hydrochloride cream) 5%. A clinical review. GemDerm Corporation, Lincoln, Illinois,1994.
4. Pipkorn U, Hammarlund A, Enerbach L. Prolonged treatment with topical glucocorticoids results in an inhibition of the allergen-induced weal-and-flare response and a reduction in skin mast cell numbers and histamine content.
Clin Exp Allergy. 1989;19:19 –25. (III)
5. Cole ZA, Clough GF, Church MK. Inhibition by glucocorticoids of the mast cell-dependent weal and flare response in human skin in vivo.
Br J Pharmacol. 2001;132:286 –292. (III)
6. Narasimha SK, Srinivas CR, Mathew AC. Effect of topical corticosteroid application frequency on histamine-induced wheals.
Int J Dermatol. 2005;44(5):425– 427. (III)
I hope this information is of help to you and your practice.
All my best.
Dennis K. Ledford, MD, FAAAAI