Tolerability of imipenem in patients with immediate hypersensitivity to penicillins

Background Administration of imipenem/cilastatin to patients with IgE-mediated hypersensitivity to penicillins who might benefit from this treatment is usually avoided because of a 47.4% rate of cross-reactivity demonstrated in a single study on the basis of positive responses to skin tests with imipenem reagents. Methods We conducted a prospective study evaluating 112 consecutive subjects who had suffered a total of 143 immediate reactions (89 anaphylactic shocks and 54 urticarial and/or angioedematous manifestations) to penicillins, mostly aminopenicillins (amoxicillin, ampicillin, and bacampicillin). All patients were skin-test positive to at least one of the penicillin reagents tested (penicilloyl-polylysine, minor determinant mixture, benzyl-penicillin, ampicillin, amoxicillin, and piperacillin). To assess the cross-reactivity with imipenem/cilastatin and its tolerability in patients displaying negative prophylactic skin tests, all subjects underwent skin testing with imipenem/cilastatin and negative subjects were challenged with it. Results One subject (0.9%) displayed a positive prick test to imipenem/cilastatin. Of the 111 subjects with negative skin tests to imipenem/cilastatin, one refused the challenge and 110 tolerated it. Conclusions Our data did not confirm the previously observed high rate of cross-reactivity between penicillins and imipenem/cilastatin. Therefore, the advisability of avoiding imipenem/cilastatin in patients with IgE-mediated hypersensitivity should be reconsidered. In those who especially require imipenem/cilastatin treatment, we recommend prophylactic skin tests, because negative results indicate tolerability.