A case of megaloblastic anemia due to vitamin B12 deficiency precipitated in a totally gastrectomized type II diabetic patient following the introduction of metformin therapy.

We wish to report a totally gastrectomized type II diabetic patient, a 67-year-old woman, who developed megaloblastic anemia due to vitamin B 12 deficiency precipitated by the introduction of metformin therapy. She was diagnosed with type II diabetes at the age of 50, and glibenclamide administration was started. At the age of 60, she received a total gastrectomy because of gastric cancer. Following gastrectomy, she was switched to insulin therapy. In June 2000, since she hoped to be switched to oral antihyperglycemic therapy, 250 mg metformin was administered two times a day instead of the insulin therapy. She had not been clinically anemic until she had started the metformin therapy (Fig. 1). Six months later, she stopped visiting our hospital because of her husband’s illness. However, she continued to take metformin for an additional four months. In April 2001, when she revisited our hospital, we found that she had developed megaloblastic anemia. While receiving the metformin therapy, she did not show any marked body weight loss and/or diarrhea. Her hematological data were as follows: hemoglobin 10.7 g/dL, red blood cell count 2.61 × 10/L, mean corpuscular volume 120.3 fl (normal 78–110), and mean corpuscular hemoglobin 41.8 pg (normal 28.0– 35.0). Her serum vitamin B 12 level fell to 131 pg/mL (normal 233–914). Since we believe that this patient’s megaloblastic anemia may have been triggered by the introduction of metformin therapy, metformin administration was immediately terminated. In addition, mecobalamin was intramuscularly or orally administered as a vitamin B 12 supplementation over a period of three months. Her megaloblastic anemia gradually improved, and was cured within three months (Fig. 1). Since July 2001, our patient has been treated with 90mg nateglinide three times daily to control her blood glucose level. After the discontinuation of the metformin therapy, she has not been clinically anemic, and her serum vitamin B 12 levels have returned to