Table 1

Summary of methodology of reviewed trials studying the effects of metformin on prediabetes

STUDYDESIGNPATIENTSTREATMENT GROUPCONTROL GROUPOUTCOME OF INTEREST
Li et al,22 1999Double-blind, placebo-controlled RCT29 938 subjects from Shougang Corporation in Beijing, China, were screened with OGTT in 1992. Of those, 1165 had IGT and were rescreened in 1994. Those already taking metformin or who had renal, hepatic, or ischemic heart disease were excluded. After rescreening, 90 still had IGT. Participants included men and women aged 30–60 yReceived 250 mg metformin TID and diabetes education (information on diet, exercise, and healthy lifestyle) every 3 mo

n = 45 (33 included in primary analysis)		Received placebo tablets identical in appearance to metformin, provided by the metformin manufacturer, and the same diabetes education as the metformin group

n = 45 (37 included in primary analysis)		Development of diabetes after 12 mo
Ramachandran et al,23 2006RCT with 4 groups:

  1. Usual care

  2. LSM

  3. Metformin

  4. LSM and metformin*

10 839 men and women, aged 33–55 y, from a middle-class Asian Indian population with no major illnesses and no pre-existing diagnosis of diabetes were screened from March 2001 to July 2002; IGT was diagnosed on basis of 2 consecutive OGTTs (FPG < 7 mmol/L; 2-h postprandial glucose 7.8–11.0 mmol/L)Received 250 mg metformin BID

n = 136 (133 available for follow-up)		Received usual care (standard health care advice)

n = 129 (128 available for follow-up)		Development of diabetes after 3 y
Knowler et al,24 2002Multicentre RCT with 3 arms:

  1. Placebo group

  2. Metformin group

  3. LSM group†

Adults 25 y and older (mean age 51 y) with FPG 5.3–6.9 mmol/L and 2-hr postprandial glucose of 7.8–11.0 mmol/L; 32% of patients were men; participants had an average BMI of 34Received 850 mg metformin BID and standard lifestyle recommendations‡

n = 1073		Received placebo tablets and standard lifestyle recommendations

n = 1082		Development of diabetes after 3 y

  • BID—twice daily, BMI—body mass index, FPG—fasting plasma glucose, IGT—impaired glucose tolerance, LSM—lifestyle modification, OGTT—oral glucose tolerance test, RCT—randomized controlled trial, TID—3 times daily.

  • ↵* We included groups 1 and 3 in our review

  • ↵† We included groups 1 and 2 in our review.

  • ↵‡ Intention-to-treat analysis was used. We also did a worst-case-scenario sensitivity analysis.