Prevention of pruritus with ethyl-chloride in skin prick test: a double-blind placebo-controlled prospective study

Background: Ethyl-chloride (EC) spray was recently shown to be an effective antipruritic agent, when given 15 min after histamine skin-prick test (SPT), without changing the wheal and flare reaction. We aimed to investigate the antipruritic effect of EC on SPT, when given prior to SPT. Methods: A double-blind placebo-controlled prospective study. Overall, 44 volunteers underwent histamine SPT on both arms to trigger local pruritus. Prior to test, they were randomly treated with EC spray on one arm and saline spray (placebo) on the other. Subjects as well as researchers were blinded to the type of applied sprays. The wheal and flare reaction was measured after the SPT and subjects reported the intensity of pruritus following EC/placebo using a validated pruritus questionnaire (indexes 1-3) and a visual analog scale (VAS). Results: Significant improvement in pruritus was reported following treatment with EC compared with placebo for all four studied parameters. Index 1 in EC 3.7 +/- 2.3 versus 5 +/- 3.5 (p = 0.007) in placebo, index 2 in EC 2.6 +/- 2.1 versus 3.8 +/- 2.8 (p = 0.002) in placebo, index 3 of EC 6.3 +/- 3.8 versus 8.8 +/- 5.8 (p = 0.03) and VAS in EC 3.7 +/- 1.9 versus 4.4 +/- 2.3 (p = 0.003). There were no significant differences between EC and placebo in terms of the wheal and flare indurations area. Conclusions: Ethyl-chloride has an effective antipruritic agent, when given before histamine SPT. Its use did not change the wheal and flare reaction, making it ideal for prevention of pruritus, secondary to allergy skin test, without masking the results.