Use of prophylactic combined H1 and H2 antagonists reduces mortality in chymopapain anaphylaxis.

The American experience concerning the epidemiology of anaphylactic reactions following chemonucleolysis with chymopapain (Chymodiactin) were presented. The first study involved 1,585 patients of whom 17% were premedicated with some drug with either an H1 or H2 antagonist or both. The rate of anaphylaxis was 0.82%. Following its clinical introduction, a postmarketing surveillance study was undertaken. During the first 30,000 cases of which 93% were premedicated with combined H1 and H2 antagonists, the frequency of anaphylactic reactions was 0.78%. Subsequently, following the introduction of an immunologic test to screen for circulating IgE, the reaction rate fell to 0.44% in 45,000 cases of which 92% were premedicated with combined H1 and H2 antagonists. Females were far more likely to experience an anaphylactic event. Overall mortality from anaphylaxis decreased from one in 800 to one in 25,000 administrations. The decreased number and severity of these reactions correspond to the development of an immunologic screening test and utilization of prophylactic antihistamines.