Skin testing in patients with high risk of anaphylactic reactions to penicillin

Sequential skin testing including immediate patch test (IPT), skin prick test (SPT), and intradermal test (IT) with sodium benzylpenicillin G (Pen G), and SPT with benzylpenicilloyl human serum albumin (BPO-HSA) was done in 58 subjects with a history of probable anaphylactic reaction or shock of unknown cause. Based on positive skin tests, the diagnosis of penicillin anaphylaxis was confirmed in 30 patients. The average age of onset of penicillin allergy was 42 years ranging from 20-70 years. The sex ratio was 2:28 with marked female predominance. Anaphylactic shock, wheezing and urticaria occurred in 21, 20, 19 patients, respectively. Most symptoms were induced by skin tests and inhalation. The results of skin tests in these patients showed that IPT with 500 U/ml of Pen G was not only reliable but also safe. It is suggested that patients suspected of penicillin anaphylaxis should received IPT with 500 U/ml of Pen G as the initial diagnostic step; if a negative reaction occurred, then SPT and IT should be applied with the same concentration of Pen G, until a positive reaction developed or all the skin testing showed negative results. SPT to BPO-HSA was safe, but its positive rate was only 47.8% in our study; it seems to be less important than skin test to Pen G. As a whole, the skin testing procedure we recommend is relatively reliable, safe and practical even in individuals extremely sensitive to penicillin. In addition, once the patient develops a positive IPT, Pen G residue on the testing site should be wiped away rapidly and washed out with cool water thoroughly to disrupt further violent reaction.(ABSTRACT TRUNCATED AT 250 WORDS)