Background: Most patients who require skin prick testing cannot deal with their pruritus without taking antihistamines (AH). Orally administered AH has a quick onset of action, but it will suppress skin test responses (STR) from several days to weeks. In this study, we aimed to determine the onset and duration of action of single topical AH application by observing histamine-STR suppression over time.
Methods: A two-step, randomized, intraindividual parallel-comparative, double-blind, placebo-controlled trial was conducted on the volar side of the forearm. Step 1 was aimed to determine the onset, while step 2 determined the duration of action. The topical AH tested was a single application of 5% doxepin hydrochloride cream, while 10 mg/ml histamine dihydrochloride was used to test the skin responses.
Results: Our 10 subjects' mean age was 35.8 +/- 3.179 years. Histamine wheal response was suppressed starting on minute 90 and the wheal width were back to >/= 7 mm(2 )on minute 270. Significant histamine reactivity difference between genders (P = 0.201) and atopic status (P = 1.000), which could be a source of bias in histamine STR, was not found among our subjects.
Conclusion: Single application of topical AH has an onset of action in 90 min and duration of action < 180 min. Because of its short duration of action, topical AH can be used in a patient who needs AH but is scheduled to undergo skin prick testing after a few hours, without influencing the patient's STR.