A recent study has found that the combination of metformin and sitagliptin lowers A1c’s better than either drug alone, apparently because their different mechanisms work together synergistically.
Sitagliptin (Januvia) is a DPP-4 inhibitor; that is, it helps prevent DPP-4 from inactivating GLP-1, a gut hormone that regulates blood glucose. (For a lesson on how that works, see “The Incretin Saga: Mimetics, Enhancers, and Inhibitors”.) Metformin (Glucophage) is an older drug that reduces the amount of glucose synthesized by the liver, decreases the absorption of glucose from the gastrointestinal tract, and increases insulin sensitivity.
The study examined 1,091 people with type 2 diabetes who were divided into four groups: sitagliptin plus metformin, sitagliptin alone, metformin alone, or a placebo. Their average starting A1c was 8.8%. After the 24-week study, 66 percent of the combo group had an A1c of less than 7%, and 44 percent of them had dropped to 6.5%.
The single drug groups also experienced improvement, but significantly less than the combo group. The incidence of hypoglycemia in the combo group was about the same as that of the placebo group.
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Sources: Medline Plus; Diabetes Care, August 2007