H2 antihistamines (cimetidine) and allergic-inflammatory reactions.

Experiments in the skin and synovialis have thrown new light on the allergic-inflammatory reactions. The inflammatory effect of histamine is thus due to stimulation of two different types of receptors in the vessels, i.e. histaminergic H1 and H2 receptors. Both types of receptors are of importance for the immediate cutaneous response to allergens and histamine. Treatment with a combination of H1 antagonists (classical antihistamines) and the H2 antagonist cimetidine will thus cause a much stronger inhibition of the urticarial reactions than treatment with the H1 and H2 antagonist alone. It is therefore probable that a combination therapy could have an advantage over the traditional treatment with classical antihistamines in urticaria and other histamine-mediated skin diseases. Histamine might also be of importance for the swelling of the joints in inflammatory diseases such as rheumatoid arthritis, and clinical trials with H1 and H2 antagonists are in progress.