Histamine and H1-antihistamines: Celebrating a century of progress

In this review we celebrate a century of progress since the initial description of the physiologic and pathologic roles of histamine and 70 years of progress since the introduction of H1-antihistamines for clinical use. We discuss histamine and clinically relevant information about the molecular mechanisms of action of H1-antihistamines as inverse agonists (not antagonists or blockers) with immunoregulatory effects. Unlike first (old)-generation H1-antihistamines introduced from 1942 to the mid-1980s, most of the second (new)-generation H1-antihistamines introduced subsequently have been investigated extensively with regard to clinical pharmacology, efficacy, and safety; moreover, they are relatively free from adverse effects and not causally linked with fatalities after overdose. Important advances include improved nasal and ophthalmic H1-antihistamines with rapid onset of action (in minutes) for allergic rhinitis and allergic conjunctivitis treatment, respectively, and effective and safe use of high (up to 4-fold) doses of oral second-generation H1-antihistamines for chronic urticaria treatment. New H1-antihistamines introduced for clinical use include oral formulations (bilastine and rupatadine), and ophthalmic formulations (alcaftadine and bepotastine). Clinical studies of H3-antihistamines with enhanced decongestant effects have been conducted in patients with allergic rhinitis. Additional novel compounds being studied include H4-antihistamines with anti-inflammatory effects in allergic rhinitis, atopic dermatitis, and other diseases. Antihistamines have a storied past and a promising future.