2014 Volume 5 Pages 29-33
A 54-year-old Japanese man who had received a diagnosis of schizophrenia and been treated with olanzapine for nearly 16 months consulted our department because of severe hyperglycemia (535 mg/dL). The use of antipsychotics, switching the patient from olanzapine to aripiprazole, and 7 weeks of insulin therapy resulted in a decrease in the patient's postprandial blood glucose levels and an increase in his postprandial C-peptide levels (442 mg/dL to 106 mg/dL and 1.72 ng/mL to 4.94 ng/mL, respectively) as well as an improvement in his pre-prandial levels (250 mg/dL to 85 mg/dL and 1.00 ng/mL to 1.69 ng/mL, respectively) with almost no change in the 24- hour urinary excretion of C-peptide. These results suggested that an insufficiency of insulin secretion, not insulin resistance, was associated with the patient's severe hyperglycemia, and that olanzapine-induced pancreatic β-cell impairment might be reversible if the hyperglycemia is diagnosed and treated sufficiently early. When prescribing second-generation antipsychotics such as olanzapine, clinicians should take the level of insulin into account in addition to monitoring serum glucose levels.