SUPPRESSIVE EFFECT OF LORATADINE ON ALLERGEN-INDUCED HISTAMINE-RELEASE IN THE NOSE

It has been speculated whether the recently developed non-sedating antihistamines may possess other properties than merely being antagonists at the H-1-receptors. To investigate this suggestion 12 patients with strictly seasonal allergic rhinitis participated in a double-blind placebo controlled randomized cross-over study outside the pollen season. At steady state levels of 10 mg loratadine, a new non-sedating antihistamine, the patients were challenged with methacholine. This as followed by a nasal challenge with increasing doses of allergen. 24 h later the patients were rechallenged nasally with the same methacholine dose as the day before. The volume of the methacholine-induced nasal secretion was measured and the response to allergen was determined by scoring technique. In returned nasal lavage fluid the levels of histamine and TAME-esterase activity were measured. It was found that loratadine significantly reduced the immediate allergic nasal symptoms compared with placebo (P < 0.01). Loratadine also reduced the allergen-induced release of histamine into the nasal cavity after the strongest allergen dose, from 9.6 +/- 1.5 (mean +/- SEM) to 6.4 +/- 1.4 ng/ml (P < 0.05). A similar decrease in the TAME-esterase activity after treatment with loratadine was observed. The TAME-esterase activity decreased from 11.6 * 10(3) +/- 2.47 *10(3) to 5.60 *10(3) +/- 1.45 *10(3) CMP (P < 0.05). There were no significant changes between the active and placebo treatments regarding the methacholine-induced secretory response. This was true for the initial methacholine challenge as well as the secretory response 24 h later. This study shows that loratadine is an effective drug in the suppression of immediate allergic nasal symptoms. One of the beneficial effects of this drug could be a reduction in allergen-induced histamine release. A finding which further implicates that antihistamines may possess other effects than just a blocking of the H-1-receptor.