AMPICILLIN AND AMOXICILLIN DELAYED-HYPERSENSITIVITY - SIDE-CHAIN-SPECIFIC ALLERGIC REACTIONS IN A CHILD

Background: Maculopapular rashes are common cutaneous adverse reaction s to ampicillin and amoxicillin. Usually they are not due to a known a llergic mechanism. However, type I (IgE mediated) and type TV (T cell mediated, delayed hypersensitivity) cutaneous reactions to beta-lactam s in general, and especially to ampicillin and amoxicillin, can be sid e-chain-specific. Case Report: A 30-month-old boy developed a generali zed maculopapular rash which progressed to desquamation while the chil d was being treated intravenously for 7 days with ampicillin. Results: When the child was 40 months old, the maculopapular rash was reproduc ed (onset, 5-8 hours) by a diagnostic oral challenge with amoxicillin (one dose, 62.5 mg). Three days after onset of the rash, he was treate d with methylprednisolone, and the rash resolved without desquamation. Penicillin V (phenoxymethyl penicillin) challenge (62.5 mg orally) an d trial (125 mg orally three times a day for 10 days) were negative. R adioallergosorbent tests to penicilloyl G and penicilloyl V were negat ive. Immediate (15 minutes) and delayed (48 hours) skin tests to penic illin G, its major and minor determinants, and cefazolin were negative before and after the challenges with amoxicillin and penicillin V. Im mediate intradermal skin tests (0.02 mt) to ampicillin (0.25 and 2.5 m g/mL) were negative. However, induration and erythema (7 x 8 mm and 10 x 10 mm) began 5 to 8 hours and reached a maximum at 48 hours after t he tests were applied. Biopsies were not done. Conclusions: These obse rvations emphasize that (1) ampicillin/amoxicillin maculopapular desqu amative rashes in children can be due to delayed hypersensitivity mech anisms, (2) betalactam ampicillin/amoxicillin delayed reactions can be side-chain-specific (amino-benzyl group), (3) ampicillin should be in cluded in skin testing protocols, (4) skin test sites should be examin ed not only at 15 minutes but also at 48 hours after the tests are app lied, and (5) other beta-lactam (not amino-benzyl) antibiotics may be tolerated.