Desloratadine is a new agent for the treatment of diseases such as seasonal allergic rhinitis and chronic urticaria. The pharmacologic profile of desloratadine offers particular benefits in terms of histamine H1-receptor binding potency and H1 selectivity. Desloratadine has a half-life of 21–24 h, permitting once-daily dosing. No specific cautions are required with respect to administration in renal or hepatic failure, and food or grapefruit juice have no effect on the pharmacologic parameters. No clinically relevant racial or sex variations in the disposition of desloratadine have been noted. In combination with the cytochrome P450 inhibitors, ketoconazole and erythromycin, the AUC and Cmax of desloratadine were increased to a small extent, but no clinically relevant drug accumulation occurred. With high-dose treatment (45 mg/day for 10 days), no significant adverse events were observed, despite the sustained elevation of plasma desloratadine levels. Specifically, desloratadine had no effects on the corrected QT interval (QTc) when administered alone, at high dose, or in combination with ketoconazole or erythromycin. Preclinical studies also show that desloratadine does not interfere with HERG channels or cardiac conduction parameters even at high dose. Desloratadine is nonsedating and free of antimuscarinic/anticholinergic effects in preclinical and clinical studies. Novel antiallergic and anti-inflammatory effects have also been noted with desloratadine, a fact which may be relevant to its clinical efficacy.