Insulin Monotherapy Versus Insulin Combined with Other Glucose-Lowering Agents in Type 2 Diabetes: A Narrative Review

CONTEXT: Insulin can be prescribed as a monotherapy or a combined therapy with other anti-diabetic medications. In this narrative review, the authors aimed to gather data related to comparison of insulin monotherapy versus combination of insulin and other anti-diabetic treatments with regards to different outcome measures in type 2 diabetes. EVIDENCE ACQUISITION: This study searched and focused on the most recently published systematic reviews and their references investigating issues related to the primary aim. RESULTS: The current data available on this topic is heterogeneous and suffers from low quality with respect to most combination treatments. Considering the efficacy and safety of combination therapy of insulin with older hypoglycemic agents, in general metformin and pioglitazone have the best and worst profiles, respectively. Compared to insulin monotherapy, combination of insulin and metformin is associated with better glycemic control, reduced daily insulin dose, less hypoglycemia, and weight gain; combination of insulin and pioglitazone results in greater hypoglycemia and weight gain and is associated with increased risk of edema and heart failure. Regarding sulphonylurea, there is some concern regarding hypoglycemia and weight gain. Addition of dipeptidyl peptidase-4 inhibitors to insulin seems to be beneficial with respect to glycemic control without any significant adverse effects. New drugs, including glucagon-like peptide-1 agonists and sodium glucose co-transporter 2 inhibitors, have acceptable profiles with significant benefits regarding weight reduction when added on insulin therapy. CONCLUSIONS: Considering the quality and longevity of evidence, compared to insulin monotherapy, insulin combined with metformin and pioglitazone has the best and worst profiles, respectively. New anti-diabetic medications have acceptable profiles yet are expensive. It is important for clinicians to meticulously weigh the advantages of combination therapy against the possible adverse effects with each drug class in every patient, individually.