Levocetirizine for treatment of immediate and delayed mosquito bite reactions.

People frequently experience whealing and delayed papules from mosquito bites. Various antihistamines have previously been tried for the treatment of this condition. We performed a double-blind, placebo-controlled, cross-over study with levocetirizine 5 mg and matched placebo in 30 adults who were sensitive to mosquito bites. On the third treatment day the subjects received two Aedes aegypti bites on the forearm. The size of the bite lesions and the intensity of pruritus (visual analogue scale) were measured. Bite symptoms could be analysed in 28 subjects at 15 min and in 8 subjects at 24 h. Levocetirizine decreased the size of wheals by 60% (p < 0.001) and accompanying pruritus by 62% (p < 0.001) compared with placebo. The effect of levocetirizine increased in a linear fashion with the size of wheals and was most significant in the subjects with largest bite lesions. Levocetirizine also decreased the size of 24-h bite lesions by 71% (p=0.008) and accompanying pruritus by 56% (p=0.016). These results show that prophylactic levocetirizine 5 mg is an effective treatment for both immediate and delayed mosquito bite symptoms and is especially effective in subjects with large wheals.