[Medicine hypersensitivity--case report].

In this paper a case of good tolerance to benzathine benzylpenicillin, but benzylpenicillin potassium allergy in subject with history of multidrug hypersensitivity was described. The same therapeutic agent is contained in both commercial drugs and dosage formulation can cause the unpredictable adverse drug reactions (ADRs). This thesis was confirmed by positive intradermal test with the same, but negative with other commercial product of benzylpenicillin potassium. Later chromatographic analysis shows drug contaminations. Thus an exclusion of allergy to drug impurities (and additives) is necessary for correct diagnosis benzylpenicillin allergy (and any active constituent). Furthermore, allergy to drug impurities (and additives) closely resemble cross-reactions or multiple chemical sensitivity syndrome (MCSS).