Allergic rhinoconjunctivitis: the role of histamine.

Allergic rhinoconjunctivitis is the most common atopic condition encountered in clinical practice. Analysis of the pathogenesis of this condition permits identification of optimal therapeutic targets. The increased knowledge of the underlying pathophysiology suggests that multiple inflammatory mediators are involved in the pathogenesis of the allergic reaction in the ocular and nasal mucosa. However, despite the presence of a wide range of different mediators, it would appear that histamine plays a key role. Experimental allergen challenge studies have demonstrated that histamine is the only mediator which produces the full spectrum of clinical manifestations of the acute allergic reaction when applied to the mucosal surface. While both H(1)- and H(2)-receptors are present in the nasal and ocular mucosa, only H(1)-receptor antagonists are capable of inhibiting histamine-induced symptoms of allergic rhinoconjunctivitis. Furthermore, although the exact role of histamine in the immediate and prolonged allergic reaction has not yet been fully elucidated, these findings do not exclude the possibility that histamine is involved in these processes. The available evidence therefore supports current clinical practice for use of H(1)-receptor antagonist as a first-line therapy in patients with this atopic condition.