11.04.2 Drugs that Modify the Actions of Histamine

H₁ receptor antagonists are also widely used for allergic conditions (rhinitis, hives, insect bites). New generation H₁ antagonists are peripherally acting and therefore less sedative than older antihistamines that cross the blood-brain barrier (e.g. cetirizine). Histamine release inhibitors (e.g. cromogylcate) can be used to prevent allergic reactions asthma. These drugs inhibit the release of histamine from mast cells, and therefore reduce histamine-induced allergy and bronchoconstriction.

H₁ receptor antagonists that act at the vestibular apparatus in the central nervous system are useful as anti-emetics and for motion sickness (e.g. promethazine), and as sedatives and for motion sickness (e.g. diphenhydramine). Some of the H₁-receptor antagonists also have some anti-cholinergic activity which also contributes to this effect.

H₂ receptor antagonists are effective in reducing acid secretion in the stomach and are used to treat peptic ulcer disease (PUD) and gastro-oesphageal reflux disorder (GORD) (e.g. ranitidine).