Antihistamines: Pharmacology and Clinical Use

Antihistamines are a diverse group of drugs which possess the ability to inhibit various histaminic actions. By and large, they bear a certain structural resemblance to histamine, and act principally to prevent histamine-receptor interaction through competition with histamine for histamine receptors. Consequently, they are helpful therapeutically in preventing, rather than reversing, histaminic actions. Individual antihistaminic drugs act to inhibit histaminic action at one or another histamine receptor (H1 or H2-receptor), but not at both receptors.