Sudden-Onset Severe Thrombocytopenia Secondary to Trimethoprim-Sulfamethoxazole.

Drug-induced immune thrombocytopenia (DITP) is a rare but life-threatening condition characterized by a sudden and serious drop in the number of platelets from drug-dependent antibodies against platelet glycoproteins. We report the case of a 57-year-old man who developed severe thrombocytopenia and mucocutaneous bleeding following a short course of trimethoprim-sulfamethoxazole (TMP-SMX) for presumed tick-borne disease. The patient experienced bleeding gums, pinpoint rashes, bruising, and extreme fatigue. The laboratory tests indicated a severely low platelet count of 1 × 1.0 × 10³/µL combined with a high immature platelet fraction (IPF). Workup for both infection and autoimmune disorders would be negative, along with the absence of intracranial hemorrhage demonstrated on imaging. The timeline and clinical picture suggested that TMP-SMX was the most likely culprit. The patient was placed on supportive care, including platelet transfusion and re-start of doxycycline after discontinuation of the drug. His platelet count began to rise, and his symptoms improved; he was discharged without issues. By presenting this instance, we place high importance on early recognition and immediate withdrawal of the offending agent to prevent life-threatening bleeding. Though confirmatory testing of antibodies is available, clinical diagnosis remains the gold standard due to delays in testing and availability.