Rapid‐Onset Thrombocytopenia Following Piperacillin‐Tazobactam Reexposure

Drug‐induced thrombocytopenia is a rare but serious adverse event that has been associated with multiple drugs including β‐lactams. Although it mostly occurs with prolonged medication use, some cases of rapid‐onset thrombocytopenia have been reported. We describe the case of a 69‐year‐old man who developed severe and immediate thrombocytopenia following reexposure to piperacillin‐tazobactam in the critical care setting. He received a 6‐day course of piperacillin‐tazobactam for a possible pneumonia immediately after cardiac surgery. During this course of therapy, his platelet count decreased (fluctuating between 69 × 10 3 /mm 3 and 104 × 10 3 /mm 3 ) and then progressively increased after completion of the antibiotic to 340 × 10 3 /mm 3 on postoperative day 15. Ten days after the antibiotic course was completed (postoperative day 16), the patient developed new signs of infection (fever and neutrophilia), and piperacillin‐tazobactam was restarted. Eight hours after reintroducing the antibiotic, his platelet count dropped from 317 × 10 3 /mm 3 to 7 × 10 3 /mm 3 . After reviewing all the medications administered to the patient as well as other potential causes of thrombocytopenia, and given the chronology of events, piperacillin‐tazobactam was suspected as the most likely offending agent and was therefore replaced by meropenem on postoperative day 17. The patient's platelet count began to rise 2 days after discontinuation of piperacillin‐tazobactam and reached 245 × 10 3 /mm 3 by postoperative day 30. No spontaneous bleeding or thrombosis occurred while the patient was thrombocytopenic. Use of the Naranjo Adverse Drug Reaction Probability Scale indicated a probable relationship (score of 6) between the patient's development of thrombocytopenia and piperacillin‐tazobactam therapy. This case highlights the severity and swiftness in which drug‐induced thrombocytopenia may present in the context of cardiac surgery.