Clinical evaluation of Pharmacia CAP System (TM) RAST FEIA amoxicilloyl and benzylpenicilloyl in patients with penicillin allergy

Background: The diagnosis of IgE-mediated immediate reactions to penicillin s can be supported by in vivo or in vitro tests using classical benzylpenic illin determinants. The wide variety of beta -lactams and the description o f new specificities requires a re-evaluation of the different tests availab le. The objective was to evaluate the diagnostic capacity of Pharmacia CAP System (TM) RAST FEIA amoxicilloyl c6 (AXO) and benzylpenicilloyl cl (BPO) in patients with a documented IgE-mediated penicillin allergy. Methods: We studied 129 patients in five groups. Groups 1, 2, and 3 had dev eloped an immediate reaction after penicillin treatment. Group 1 (n= 19) we re skin test positive to amoxicillin (AX) and/or BPO and/or minor determina nt mixture (MDM); group 2 (n = 29) were skill test positive to AX but negat ive to BPO and MDM; and group 3 (n = 26) were skin test negative to all det erminants, the diagnosis being confirmed by a previous repetitive history o r controlled administration. Two control groups, one with nonimmediate reac tions - group 4 (n = 25) - and one with good tolerance to penicillin - grou p 5 (n = 30) - were included. All samples were analyzed in vitro for AXO an d BPO, and the results compared to the in vivo diagnosis. Results: AX was the drug most often involved. In group 1, 53%, were in vitr o positive for AXO and 68% for BPO, but 74%, had at least one positive test result. In group 2, only 10%, had a positive in vitro test to BPO compared to 41% to AXO. In group 3, 42% had positive BPO and/or AXO in vitro tests. In the control groups 4 and 5, the negative in vitro results for AXO were 96% and 100%, and for BPO 100% and 97%, respectively. A positive correlatio n between specific IgE levels and the time interval from the reaction to th e evaluation was found only for group 3. Conclusions: This in vitro assay is beneficial for evaluating subjects alle rgic to beta -lactams. It is necessary to test for specific IgE to AXO in a ddition to BPO in patients with immediate allergic reactions after AX. The combination of in vim and in vitro tests for estimating IgE antibodies to p enicillins is important because of the existence of patients with a positiv e history but negative skill test.