This review will focus on primarily on chronic spontaneous urticaria (CSU) characterised by the occurrence of itchy, short-lived weals ranging from a few millimetres to several centimetres in diameter which are accompanied by severe itching which is usually worse in the evening or night-time.Histamine, which is a key contributor to the symptoms of this condition, reaches very high concentrations due to the poor diffusibility of substances in the dermis. H1-antihistamines have been used for more than fifty years in treating various allergic manifestations. H1-antihistamines which penetrate into brain elicit, by inhibiting stimulant effect of histamine, drowsiness.In addition to this antihistamine effect, they can have parallel pharmacological properties, for example antimuscarinic and adrenolytic effects which must be considered.In a study of 51 patients treated with cetirizine at a dosage of 10 mg once daily, 18 patients had an inadequate response and were randomized to further treatment with either cetirizine 20 mg once daily or olopatadine 5 mg twice daily.Patients in the increased cetirizine dose group showed significant improvements in the severity of wheal and itching and in quality of life.Clinical studies sponsored by the manufacturer have shown that bilastine 20 mg once daily is as efficacious as other nonsedating antihistamines in allergic rhinoconjunctivitis and chronic urticaria in individuals from 12 and 18 years of age, respectively.
Antihistamines are inhibitors of histamine receptors. H1-antihistamines, inhibit competitively H1 receptors and the corresponding effects i. They do not inhibit antigen/antibodies reactions, nor histamine release, they inhibit H1 effects.Other H1-antihistamines having an important antimuscarinic activity like diphenhydramine and dimenhydrinate, are used in preventive and curative treatment of motion sickness, but scopolamine which has no antihistamine effect seems more effective than them in preventive treatment.In patients with urticaria resistant to the standard dosage of cetirizine or fexofenadine, doubling the daily dose may be effective.The first-genaration antihistamines have alpha adrenolytic activity which can decrease the vasoconstrictive effect of adrenaline and noradrenaline and an antimuscarinic effect with the corresponding adverse effects.Certain H1 antagonists, such as promethazine, have a local anesthetic effect.