Severe Thrombocytopenia Possibly Associated with TMP/SMX Therapy

OBJECTIVE: To report a case of possible severe, life-threatening thrombocytopenia associated with trimethoprim/sulfamethoxazole (TMP/SMX) therapy. CASE SUMMARY: A 54-year-old white woman received a 10-day course of TMP/SMX for treatment of chronic sinusitis. One day after finishing the course of TMP/SMX therapy, she presented to the emergency department because of the development of scattered petechiae on both hands and blood blisters in her mouth. On admission, her complete blood cell count results revealed a severely low platelet count of 2 × 10 3 /mm 3 . Other laboratory test results were normal, except for elevated blood glucose (nonfasting blood glucose). TMP/SMX was believed to be the most likely cause of thrombocytopenia. She was treated successfully with a transfusion of 2 units of platelets and oral prednisone. Her platelet count increased to 110 × 10 3 /mm 3 4 days after discontinuation of TMP/SMX. She was discharged on hospital day 5. On follow-up (2 wk after hospital discharge), her platelet count was normal (351 × 10 3 /mm 3 ). DISCUSSION: TMP/SMX has been implicated as a cause of thrombocytopenia, which is defined as platelet count <150 × 10 3 /mm 3 . Although it is uncommon, spontaneous severe bleeding may occur when platelet count decreases to ≤10 × 10 3 /mm 3 . Thrombocytopenia associated with TMP/SMX appears to be an immune-mediated process resulting in platelet destruction by drug-dependent platelet antibodies. Treatment of thrombocytopenia associated with TMP/SMX therapy includes discontinuation of the offending drug and the use of corticosteroids. Platelet transfusion and intravenous immunoglobulin may be required in some patients. CONCLUSIONS: Thrombocytopenia associated with TMP/SMX therapy can be serious or life threatening because it may result in significant bleeding complications. This hematologic adverse effect of TMP/SMX may occur even with the usual recommended dosage and duration of therapy. Careful monitoring of complete blood cell count, including platelet count, before and during TMP/SMX therapy is suggested.