The tendency to bleed after administration of broad spectrum antibiotics, particularly those of the cephalosporin group, has attracted attention in recent years. The predominant opinions are that this is due to two mechanisms, namely, thrombocytopenia, and impaired prothrombin synthesis from Vitamin K deficiency attributable to a decrease in the population of intestinal flora. This patient was a 58 year old male with hypopharyngeal squamous cell carcinoma (rT1 N0M0) who had undergone resection

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... f the hypopharyngeal portion with reconstruction using a pectoralis major myocutaneous flap. A drain retained in the anterior chest wall was removed after confirming the absence of abnormality on the 8th day after the operation, and thereafter the clinical course was uneventful. However, on the 14th day, a hematoma formed in the anterior chest wall, below the axilla. Within several days, the hemoglobin levels fell from 10.2g/dl to 6.5 g/dl and the white blood cell count increased from 7500/mm2 to 16200/mm2, resulting in the necessitation of blood transfusions. These numbers, coupled with results showing platelet counts of 709,000/mm2, prothrombin time of 26.2sec (15%), A-PT time of 76.0sec, fibrinogen levels of 588mg/dl and normal FDP, suggested that Vitamin K2 deficiency due to the antibiotics, rather than DIC was responsible. Intravenous administration of Vitamin K2 was immediately started. After several days, the hematoma ceased to grow, and the results of the hemostatic test returned to normal. The patient's general condition improved by the 28th day after the operation, and an operation to remove the hematoma was perfomed. The patient's recovery progressed favorably, and he was discharged.