Limitations
This study had a few limitations. Its design was retrospective, and its narrow demographics may not permit generalizability to other patient populations. In addition, the study evaluated initiation of new medications at time of discontinuation of metformin but not dosage adjustments of current medications. Insulin type and dosage were not evaluated—only whether insulin was initiated. Further, follow-up time was limited; change in long-term glycemic control requires more study. Another limitation was that adherence could not be assessed.
Conclusion
After discontinuation of metformin, there was a statistically significant increase in HbA1c level. Insulin was initiated in 51% of patients after discontinuation of metformin. Subgroup analysis of the patients who started insulin after discontinuation of metformin revealed the same HbA1c levels before and 1 year after discontinuation with a loss of glycemic control throughout the year. Of the 47 patients who were initiated on insulin, 20 had their SCr level decrease to < 1.5 mg/dL and could have been restarted on metformin. This finding indicates that many patients may have been able to delay time to insulin initiation and maintain the same glycemic control if metformin could have been continued. With more study, long-term change in glycemic control after discontinuation of metformin can be determined. In many patients, metformin is needed for adequate glycemic control. The revised FDA labeling allows many patients with mild-to-moderate kidney disease to benefit from treatment with metformin.