Antihistamines in urticaria.
Urticaria is one of the most common and, in its chronic course, excruciating dermato-allergic diseases. Apart from the dermatological diagnosis, the identification and evaluation of causal triggering factors is of utmost importance. Here a 'three-step guideline' (according to Ring and Przybilla) has gained acceptance, ranging a general basic examination via an intensive investigation until oral provocation tests for food allergy and oral provocation tests for idiosyncrasy (OPTI) against food additives. Apart from true IgE-mediated allergies, pseudo-allergic reactions against food additives as well as food contents represent a major problem in chronic urticaria. Recently gastric mucosal colonization with Helicobacter pylori as the trigger of chronic urticaria has received attention. New pathophysiological concepts describe autoantibodies that are directed either against IgE or against the high-affinity IgE-receptor on the surface of mast cells and basophil leucocytes. In the intradermal test with autologous serum positive wheal and flare reactions can be observed (Greaves' test). In many patients with chronic urticaria considerable psychosomatic involvement is also observed. Histamine is one of the major mediators of most forms of urticaria although in some cases, especially physical urticaria, other mediators seem to play a role. Therefore antihistamines, and mainly H1 antihistamines, are the mainstay of antiurticaria therapy. Some studies have shown a benefit of combined H1- and H2-antagonist treatment in special forms of urticaria namely urticaria factitia. Similarly pretreatment with combined H1 and H2 antagonists has been proven to reduce effectively the frequency of pseudo-allergic reaction to some histamine-releasing drugs used in radiology or surgery. More than 50 years after the first introduction of an antihistamine into allergy therapy, antihistamines still represent modern and exciting agents contributing to the continuous improvement of antiallergic therapy. Antihistamine therapy can be performed with either the classical or second generation antihistamines. Classical antihistamines are connected with considerable side-effects especially sedation and anticholinergic effects. New non-sedating antihistamines have been developed that do not cross the blood-brain barrier. The efficacy of mizolastine, a new non-sedating H1 antagonist, has been evaluated in several placebo-controlled and comparative clinical trials. Overall, mizolastine 10 mg/day was found to be significantly more effective than placebo and as effective as other second generation antihistamine drugs in the management of patients with chronic urticaria, with a rapid and sustained action.