Routine use of skin testing for immediate penicillin allergy to 6,764 patients in an outpatient clinic.

A population of 6,764 individuals who had received a penicillin prescription at an outpatient clinic was tested with MDM (minor determinant mixture) and PG (penicillin G), whether or not a previous history of allergy to penicillin had been reported. Ninety-six (1.4%) patients showed positive skin tests. The 6,668 patients with negative tests were treated with penicillin and none showed any immediate allergic reaction. Because of the large size of the sample it was possible to calculate that the probability of risk of systemic reactions among patients with negative tests who were immediately treated with penicillin was 1.5/million. The method used is simple to carry out and has proved to be safe and reliable for the identification or exclusion of immediate allergic reaction to penicillin.