Role of antihistamines in allergic disease.

Both first-generation and second-generation antihistamines effectively reduce symptoms of sneezing, rhinorrhea, and nasal pruritus in individuals with allergic disease. These agents act as competitive inhibitors of histamine (a principal mediator of the allergic response) at various target-organ sites. Although the classic, first-generation antihistamines are unable to halt the allergic reaction once it has begun, emerging evidence has suggested that newer, second-generation agents may interfere with the release of inflammatory mediators from mast cells or may inhibit eosinophil chemotaxis. These effects may confer additional clinical benefit. Also, the second-generation agents produce fewer adverse reactions, including a marked reduction in sedation. Contrary to previous recommendations, recent findings have suggested that antihistamines may not necessarily be contraindicated in patients who have both asthma and allergic rhinitis. A greater understanding of the mechanisms of action and clinical effects of both older-generation and newer-generation antihistamines should help define optimal therapeutic strategies in the future.