Onset of action of loratadine and placebo and other efficacy variables in patients with seasonal allergic rhinitis.

In a double-blind study, 185 patients with seasonal allergic rhinitis were randomly assigned to receive 10 mg of loratadine or placebo once daily for three days. On day 1 of treatment, the onset of relief of symptoms within 30 minutes of drug administration was reported by 13% of the loratadine-treated patients and by 4% of the placebo patients (P less than 0.05). At two hours after drug administration, 65% of the loratadine-treated patients and 48% of the placebo patients reported symptom relief. On day 3, the loratadine-treated patients reported a significantly greater relief of symptoms, and according to both physician and patient evaluations, the treatment response was significantly superior in the loratadine-treated than in the placebo patients. The incidence of sedation was 2% in the loratadine group and 1% in the placebo group.