[Use of patch-scratch tests to determine penicillin and cephem allergies]

The drug eruptions caused by penicillins and cephems and the patch-scratch test reactions to these drugs are discussed herein. Five hundred eighty two patients were diagnosed with drug eruption as a result of patch-scratch tests, history, gurgle tests or challenge tests in the 22 years from 1971 to 1992 in our department. Of these cases 53.8% were caused by penicillins, and 29.9% by cephems. The number of cases of allergic reactions to both, especially cephems has been increasing steadily over the last 10 years. Patch-scratch tests were performed on 382 patients among 385 patients with drug eruption caused by penicillin or cephem out of the 582 patients above mentioned. Among these patients, the patch-scratch test positive rate for penicillins and cephems was 84%, suggesting that the patch-scratch test is useful for identifying penicillin and cephem allergies. Patch-scratch tests for our antibiotics series were performed on 1256 patients with drug eruption or contact dermatitis caused by some allergens, whether the allergens were penicillins or cephems, or neither, 29.5% of these showed positive reactions to penicillins and 12.7% to cephems. Among these patients, patch-scratch tests for our penicillin and cephem series were also performed on 81 patients, 88.9% of whom showed positive reactions to penicillins and 59.3% to cephems. The highest incidence of positive reactions, 77.8%, occurred with wide spectrum semisynthetic penicillins. Of this group, ampicillin had the highest incidence at 58%. In 32 cases, the allergen could be detected. As to the clinical types of these cases, maculopapular eruptions and erythroderma showed the highest incidence. Cross reactions also occurred within the same group, most being for wide spectrum semisynthetic penicillin. The optimum concentration of each allergen used in the patch-scratch tests was evaluated on the basis of the relationship between the concentration of the allergens and the results of the patch-scratch tests. The results were 20w/w% in ABPC, AMPC, SBPC, CER, CMZ, CZX and LMOX, 10 w/w% in PCG and CBPC, 5w/w% in CMD. Drug lymphocytic stimulation tests were performed in 12 cases, with 15 drugs producing positive patch-scratch test reactions. Only 3 drugs showed positive reactions, suggesting that this test is unreliable.