Background: In type 2 diabetes mellitus (T2DM), progressive loss of beta cell function over time requires treatment intensification and eventually initiation of insulin for many patients. Relative to metformin, a greater rate of decline in beta cell function over time has been observed with sulfonylurea treatment. The present study examined the association between initial monotherapy with metformin or sulfonylurea and subsequent initiation of insulin in older subjects with T2DM.
Methods: In a retrospective cohort study using the GE electronic medical record database, eligible subjects with T2DM included those ≥65 years who received their first prescription of sulfonylurea or metformin as initial monotherapy between January 1, 2003 to December 31, 2008. The follow-up period lasted to the end of 2009 or the subject's latest data available. Insulin initiation was determined by prescription records. Logistic regression analysis evaluated the likelihood of insulin addition. A Cox regression model estimated time to initiation of insulin. Differences in baseline characteristics were controlled for using propensity score matching.
Results: Overall, 12,036 subjects were included in the analysis. Mean age was 75 years and 50% were male. Subjects who initiated with sulfonylurea had a significantly (P < 0.001) higher incidence of insulin addition (2.8% vs. 1.4%) compared to those initiated with metformin within 1 year of follow-up. The likelihood of initiating insulin was higher in subjects initiated with sulfonylurea than with metformin (adjusted odds ratio 1.82, 95% confidence interval [CI] 1.40-2.38; P < 0.001). Sulfonylurea use was also significantly associated with a shorter time to insulin use compared to metformin (adjusted hazards ratio 2.10, 95% CI 1.83-2.39; P < 0.001).
Conclusion: In a cohort of older subjects with T2DM initiating antihyperglycemic therapy, new users of sulfonylurea monotherapy were more likely to receive insulin therapy and received it earlier than those starting with metformin.