Objective: To determine the change in the hepatic insulin resistance index (HIRI) after metformin treatment.
Methods: In this retrospective cohort study, Mexican mestizo patients with a body mass index (BMI) of 25 kg/m(2) or greater were evaluated. Participants were classified into 2 groups: patients who received metformin and patients who did not. Both groups were followed up for a median of 6 months (range, 4-10 months). The HIRI was calculated at baseline and at follow-up in both groups. We evaluated the independent effect of metformin on HIRI after adjustment for the difference in basal and final values (DELTA) of BMI, waist circumference, glucose, and insulin.
Results: A total of 71 patients were enrolled (51 [72%] female). Forty-one patients received metformin and 30 patients did not. Mean age was 36.3 ± 12.2 years and mean BMI was 42.2 ± 10.7 kg/m(2). After metformin treatment, HIRI significantly decreased from 38 ± 10.7 to 34.7 ± 9.5 (P = .03). In contrast, the control group had a nonsignificant increase in HIRI (37.6 ± 11.7 to 40.0 ± 14.0, P = .22). Weight significantly decreased in both groups (group 1: 114.6 ± 33.8 kg to 107.6 ± 28.9 kg, P<.01; group 2: 104.8 ± 28.5 kg to 98.9 ± 26.0 kg, P<.01). After BMI adjustment, the total metformin dosage correlated negatively with HIRI (r = -0.36, P = .03). Using a linear regression model (F = 6.0, r2 = 0.37, P = .002) adjusted for DELTA BMI and DELTA waist circumference, the administration of metformin resulted in independent improvement in the HIRI level (standardized β = -0.29, t = -2.0, P = .04).
Conclusions: Metformin improves HIRI independently of anthropometric changes. In persons with elevated HIRI levels, metformin may be considered among the treatment options.