Abstract
Thiamine (vitamin B1) is generally considered safe, with rare adverse effects, including anaphylaxis. Although thrombocytopenia related to thiamine deficiency is known to improve with supplementation, thrombocytopenia occurring after thiamine administration has not been well described. We report the case of a 63-year-old female with adrenal insufficiency and malnutrition who developed severe thrombocytopenia shortly after initiation of intravenous thiamine for nutritional support. Platelet counts declined rapidly during therapy and recovered completely following thiamine discontinuation, with no alternative etiology identified after systematic evaluation. Drug-induced immune thrombocytopenia was suspected, with Naranjo score of 6 indicating a probable adverse drug reaction; the temporal relationship and clinical course were consistent with this diagnosis. No alternative causes were identified. This case highlights a rare and previously undocumented association between thiamine therapy and thrombocytopenia. Clinically, this report demonstrates that even medications generally regarded as safe may, in rare cases, lead to serious hematological adverse effects, underscoring the importance of reporting such events to increase clinical awareness of this uncommon but potentially severe reaction. Clinicians should maintain a high index of suspicion for drug-induced thrombocytopenia in patients receiving intravenous thiamine and consider platelet monitoring in high-risk or critically ill patients.