Andrew V. Doodnauth¹, Shruthi Sivakumar¹, Yohannes Mulatu¹, Eilliut Alicea¹, Samy I. McFarlane^1,

Objective: To report a case of life-threatening thrombocytopenia associated with the use of trimethoprim/sulfamethoxazole (TMP/SMX) therapy. Report of the case: 50-year-old woman with no significant past medical history who presented with one day of petechial rash on her arms, chest and legs. Patient reports that she had just completed a 7- day course of TMP/SMX (1-double strength tablet twice a day) for uncomplicated UTI by her PMD. On admission, the patient was hemodynamically stable, and complete blood cell count revealed a platelet count of 2000/uL. TMP/SMX was believed to be the most likely cause of thrombocytopenia. After discontinuation of TMP/SMX and treatment with 2 units of platelets, 1gm intravenous immunoglobulin (IVIG) and oral dexamethasone, repeat CBC showed a stable platelet count of 90,000/uL. Patient was successfully discharged on hospital day 3 with outpatient follow up with the hematology clinic for further monitoring. Conclusion and Discussion: Differential diagnosis of severe thrombocytopenia include drug induced thrombocytopenia (DITP), thrombotic thrombocytopenic purpura (TTP), post transfusion purpura (PTP), immune thrombocytopenic purpura (ITP), heparin induced thrombocytopenia (HIT), or catastrophic antiphospholipid antibody syndrome (APS). Drug-dependent antibodies are an unusual class of antibodies that bind firmly to specific epitopes on platelet surface glycoproteins only in the presence of the sensitizing drugs. DITP typically has an abrupt onset of severe thrombocytopenia, usually less than 20,000/uL. Thrombocytopenia usually begins to recover within 1-2 days after the offending drug is discontinued and platelet levels usually normalize within one week as demonstrated in our case report. Pharmacological treatment can include platelet transfusions in case of severe, overt bleeding, corticosteroids or IVIG administration. In most cases, however, discontinuation of the offending drug is sufficient.

thrombocytopenia, trimethoprim/sulfamethoxazole, bactrim, adverse drug reaction