The METRO study: a retrospective analysis of the efficacy of metformin for type 2 diabetes in Japan

Endocr J. 2023 Jan 30;70(1):121-128. doi: 10.1507/endocrj.EJ22-0330. Epub 2022 Oct 18.


Metformin monotherapy as first-line treatment for patients with type 2 diabetes (T2D) has been shown to effectively improve blood glucose levels and motivation to undergo treatment and prevent complications. However, no studies have reported its effect when combined with other drugs or compared the effect based on administration time. This study aimed to investigate the effect of metformin administration in Japanese patients with T2D, examine how the introduction line impacts the effect of metformin, and examine the characteristics of patients demonstrating improved blood glucose levels. Data on characteristics of patients who were newly prescribed metformin with no shifting of hypoglycemic agents in the subsequent 24-week observation period, and their age [mean, 56.8 years], body mass index [mean, 27.5 kg/m2], glycated hemoglobin [HbA1c] [mean, 8.1%], and duration of diabetes [mean, 3.0 years] were obtained from the medical records of 201 patients. The changes in HbA1c by introduction line after 24 weeks were -1.59%, -0.91%, -0.89%, and -0.65% in the first, second, third, and fourth induction lines, respectively; earlier introduction more significantly improved blood glucose. The factors significantly associated with HbA1c changes were early introduction, high baseline HbA1c, high estimated glomerular filtration rate, decreased insulin secretion, short estimated duration of diabetes, and increased metformin dose. Furthermore, factors contributing to the largest HbA1c improvement by metformin were high baseline HbA1c and early administration. Metformin is expected to lower blood glucose levels in Japanese patients with T2D, even in those with decreased insulin secretion, due to its early introduction as a first-line drug.

Keywords: First-line therapy; Glycated hemoglobin; Insulin resistance; Metformin; Type 2 diabetes.

MeSH terms

  • Blood Glucose
  • Diabetes Mellitus, Type 2* / drug therapy
  • Drug Therapy, Combination
  • Glycated Hemoglobin
  • Humans
  • Hypoglycemic Agents / therapeutic use
  • Japan
  • Metformin* / therapeutic use
  • Middle Aged
  • Retrospective Studies
  • Treatment Outcome


  • Metformin
  • Blood Glucose
  • Glycated Hemoglobin
  • Hypoglycemic Agents