Urticaria

Acute urticaria (named after its similarity to the sting of a nettle, Urtica) and angioedema usually respond well to Hj receptor antihistamines, although severe cases are relieved more quickly with use of adrenaline (epinephrine) (adrenaline injection 1 mg/ml: 0.1-0.3 ml, s.c.). A systemic corticosteroid may be needed in severe cases.

In some individuals, urticarial weals are provoked by physical stimuli, e.g. friction (dermographism), heat or cold. Exercise may induce weals, particularly on the upper trunk (cholinergic urticaria). Physical urticarias may require combined J I,- and H2-receptor receptor antagonists fully to block the vascular effects of histamine, which causes flushing and hypotension. Cyproheptadine is usually the preferred choice of Hj-antihistamine but causes drowsiness.

Chronic urticaria usually responds to an H^ receptor antihistamine with low sedating properties,

11 The risk of birth defect in a child of a woman who has taken isotretinoin when pregnant is estimated at 25%. Thousands of abortions have been done in such women in the USA. It is probable that hundreds of damaged children have been born. There can be no doubt that there has been irresponsible prescribing of this drug, e.g. in less severe cases. The fact that a drug having such a grave effect is yet permitted to be available is attribute to its high efficacy.

e.g. cetirizine or loratidine. Terfenadine is also effective, but may cause dangerous cardiac arrhythmias if the recommended dose is exceeded or if it is administered with drugs (or grapefruit juice) which inhibit its metabolism.

Hereditary angioedema, with deficiency of Cj-esterase inhibitor (a complement inhibitor), may not respond to antihistamines or corticosteroid but only to fresh frozen plasma or preferably ^-inhibitor concentrate. Delay in initiating the treatment may lead to death from laryngeal oedema (try adrenaline (epinephrine) i.m. in severe cases). For long-term prophylaxis an androgen (stanozolol, danazol) can be effective.

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