Efficacy of immediate-release versus extended-release metformin on glycemic control and insulin resistance in Saudi patients with type 2 diabetes: A prospective cohort study.

Objectives: Metformin, the first-line treatment for type 2 diabetes mellitus (T2DM), is available in both immediate-release (IR) and extended-release (XR) formulations. Limited data exist comparing their effects on glycemic control and insulin resistance among Saudi patients. This study aims to evaluate the impact of metformin IR versus XR on glycated hemoglobin (HbA1c), fasting blood glucose (FBG), fasting serum insulin (FSI), and insulin resistance (HOMA-IR) in newly diagnosed Saudi T2DM patients. Methods: In a 6-month prospective cohort study at a Saudi diabetes center, 119 adults with newly diagnosed T2DM (62 on metformin IR, 57 on metformin XR) were followed. Glycemic parameters (HbA1c, FBG) and insulin resistance indices (FSI, HOMA-IR) were measured at baseline and after a 6-month follow-up. Within-group changes were assessed, and outcomes were compared between the IR and XR groups. Results: Both formulations significantly improved glycemic control from baseline. HbA1c was reduced from 7.3 % at baseline to ∼6.5 % with metformin XR, versus ∼7.6 %-∼7.2 % with metformin IR. XR achieved a greater adjusted mean HbA1c reduction by 31 % than IR (p < 0.05). FBG improved in both groups with no significant statistical difference between groups (p = 0.111). Despite better glycemic declines with XR, FSI and HOMA-IR improved substantially with no statistically significant difference between groups (p > 0.05). Conclusions: In newly diagnosed Saudi patients with T2DM, metformin XR showed better reduction in long-term glycemic control compared to IR, while both formulations similarly reduced insulin levels and resistance. XR's enhanced glycemic efficacy, achieved without differences in insulin resistance effects, may reflect improved adherence and sustained drug delivery.