Two hundred and twenty consecutive patients, referred for intravenous pyelography, weré assessed for adverse reactions. The effect of prophylactic antihistamines was evaluated. Patients were divided randomly into control, saline or chlorpheniramine treated groups. Changes in serum total haemolytic complement (CH50) and immune complexes (IC) at times 0, 1, 5, 10 and 20 min after injection of radiocontrast material were assayed. Forty-two of the 220 patients suffered reactions, classified clinically into allergic and non-allergic types.
There was no difference in the incidence of allergic reactions between control and saline groups. However, significantly less (P < 0.05) allergic reactions were noted in the antihistamine pre-treatment group. Depressed CH50 occurred in forty-three, of eighty-eight patients tested and persisted for at least 20 min in twenty-two. There was no correlation between CH50 depressions and clinical symptoms. The IC remained unchanged throughout. In conclusion, prophylactic antihistamines may diminish the incidence of allergic reactions. Complement activation occurs in a large number of patients, unrelated to symptomatology, and does not appear to be the only factor responsible for adverse reactions.