Allergy to penicillin unsuccessfully treated with a haptenic inhibitor (benzyl-penicilloyl-N2-formil-lysine; BPO-flys). A case report.

In a patient with a past history of allergy to penicillin and requiring treatment, skin tests with penicillin and penicilloyl-polylysine (PPL) were positive, and a penicilloyl RAST was strongly positive, although the Prausnitz-Küstner test to penicillin and PPL were negative. The haptin BPO-Flys was administered together with penicillin to try to prevent reactions. An anaphylactic reaction occurred on the fifth day, and treatment was stopped. Serum total IgE values increased markedly after the reaction and PK titres to penicillin and PPL reached values of 1/256. The skin test reaction to PPL was negative the day after the clinical reaction, but became strongly positive again a few days later. The penicilloyl RAST remained strongly positive throughout. The authors consider that there was hypersensitivity to a penicillin metabolite other than the penicilloyl group, e.g. to minor determinants, and for this reason the hapten inhibitor failed.