Immediate Hypersensitivity to Rifampicin in 3 Patients: Diagnostic Procedures and Induction of Clinical Tolerance.

Background: Desensitization with drugs may be indicated in some clinical situations. Apart from large experiences with β-lactam antibiotics and cotrimoxazole in HIV infection, experience with other drugs is limited. Rifampicin may elicit exanthema and urticaria, and their pathomechanisms are not known in detail. Since therapy with rifampicin may be indispensable in mycobacterial infections or against multiresistant Staphylococcusaureus, desensitization may be indicated in some patients. Objective: Report of immediate hypersensitivity to rifampicin and description of diagnostic and desensitization procedures. Methods: We report 3 patients with immediate urticarial reactions to rifampicin. Diagnostic procedures included skin and in vitro tests (specific IgE, lymphocyte transformation test, LTT, and CAST®). The non-irritant cutoff concentration was evaluated in 24 volunteers. A 7-day desensitization procedure was used. Results: Only intradermal tests at a dilution of at least 1:10,000 (concentration of rifampicin approximately 0.006 mg/ml) were true positive, whereas in vitro tests (IgE, LTT and CAST) did not correctly identify hypersensitive patients. Two patients had positive accidental reexposure. All patients were successfully desensitized with rifampicin according to a slow 7-day protocol. Conclusions: Rifampicin rarely elicits immediate hypersensitivity symptoms which may be diagnosed by intradermal skin tests. In vitro tests did not contribute to the diagnosis. Therefore, an IgE-mediated mechanism remains to be proven. Desensitization with rifampicin using different protocols has been reported. In our 3 cases, clinical tolerance to rifampicin was achieved using a 7-day protocol. Copyright © 2006 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]