BACKGROUNDDrug‐induced immune thrombocytopenia (DITP) is an adverse drug reaction associated with platelet (PLT) destruction by drug‐dependent antibodies. Demonstration of drug‐dependent PLT antibodies is often difficult and can only be rendered by extensive laboratory testing. In this report, we present the first serologically confirmed case of DITP caused by the antibiotic flucloxacillin.CASE REPORTA 68‐year‐old man developed severe thrombocytopenia that was first suspected to be related to heparin‐induced thrombocytopenia. The absence of PLT‐activating heparin‐dependent antibodies and the abrupt decrease in PLT count to fewer than 20 × 109/L raised the suspicion of DITP.DISCUSSIONFlucloxacillin‐dependent antibodies were detected in patient serum using whole PLT enzyme immunoassay and flow cytometry. The glycoprotein (GP) specificity was identified to be against GP IIb/IIIa complexes using the monoclonal antibody immobilization of PLT antigens assay. Interestingly, antibody binding was abolished when EDTA plasma was used and restored after adding calcium.CONCLUSIONIn summary, DITP should be considered in cases of acute thrombocytopenia during treatment with flucloxacillin.