Onset of action in the nasal antihistaminic effect of cetirizine and loratadine in patients with allergic rhinitis

Several studies have compared the cutaneous efficacy of cetirizine and loratadine and their onset of action. We assessed the nasal effect of these two antihistamines in a randomized, double-blind, crossover, placebo-controlled trial in order to compare objectively their efficacy and onset of action in the noses of patients with allergic rhinitis. Nasal challenge was performed by nebulization of increasing doubling doses of histamine (0, 0.04-1.28 mg/nostril) in 12 patients (eight men, four women, aged 22-39 years). Nasal airway resistance (NAR) was measured by posterior rhinomanometry either 1.5 h or 4 h after intake of cetirizine (10 mg), loratadine (10 mg), or placebo. Baseline NAR was identical between all study days (2.60-2.88 cmH₂O·1⁻¹·s). One and a half hours after intake, the increase in NAR induced by histamine was significantly reduced by both cetirizine and loratadine in contrast to placebo. However, with cetirizine the nasal obstruction was significantly lower than with loratadine ( P <0.05). Four hours after intake, a similar inhibition of the nasal obstruction caused by histamine was observed with both cetirizine and loratadine ( P <0.05). In conclusion, this study found cetirizine and loratadine to have similar nasal efficacy at therapeutic dosage 4 h after intake, whereas cetirizine was more effective than loratadine 1.5 h after intake. In agreement with the results observed in the skin, our study suggests a more rapid onset of action of cetirizine in the nose in allergic rhinitis.