Objective: To compare serum concentrations of inflammatory cytokines, interleukin 6 (IL-6), high-sensitivity C-reactive protein (hs-CRP), adiponectin, and tumor necrosis factor α (TNFα), before and after 3 months treatment with metformin in obese adolescents with insulin resistance (IR).

Design and subjects: This was a randomized, double-blinded, clinical trial of two groups of obese adolescents with IR, aged 9–18 years: a placebo group (n= 14) and a metformin group (n= 12) who received 500 mg metformin every 12 h for 3 months. Anthropometric and biochemical (metabolic and inflammatory cytokines) assessments were compared at the beginning and end of treatment.

Results: After 3 months of treatment, body mass index (kg/m 2) was reduced in both groups: placebo group (32.82±6.37–32.10±6.52; p= 0.011) and metformin group (33.44±5.82–32.71±5.77; p= 0.015). Serum fasting insulin concentrations (pmol/L) increased in the placebo group (189.45±112.64–266.06±167.79; p= 0.01) and showed a slight decrease in the metformin group (256.82±113.89–229.25±86.53; p= 0.64). Adiponectin concentrations (μg/mL) decreased in the placebo group (13.17±7.31–5.65±6.69; p= 0.02), while these remained stable in the metformin group (8.57±3.98–7.86±6.23; p= 0.64). In the metformin group, significant reductions were found in the variances of serum TNFα concentrations (p= 0.006; Levene test).

Conclusion: These results suggest that treating obese adolescents with IR using metformin for 3 months is an option for patients without response to traditional lifestyle change because metformin improves inflammatory activity, which is an etiological factor in cardiovascular disease development.