Figure 2From: Antihistaminic, Anti-Inflammatory, and Antiallergic Properties of the Nonsedating Second-Generation Antihistamine Desloratadine: a Review of the EvidenceH 1 -receptors may be activated by an antagonist, such as histamine (A) or exhibit spontaneous basal, or constitutive, activity in the absence of ligand binding (B). Anti-histamines repress both histamine-induced and constitutive activity, eventually restoring the receptor to an inactive state (C). AH, antihistamine; H, histamine.Back to article page