What do you think of using an a-glucosidase inhibitor, such as acarbose (Precose), with a dipeptidyl peptidase IV (DPP-IV) inhibitor, such as sitagliptin (Januvia)? Would the combination be additive or synergistic? Or would it be contraindicated? Both agents lower hemoglobin A1c.
—Joseph Nelson, MD, Pauma Valley, Calif.

Similarly, are there any data on the safety of combining sitagliptin and an incretin mimetic glucagonlike peptide-1 (GLP-1) like exenatide (Byetta)?
—Zosimo A. Adefuin, MD, Bridgeport, Conn.

I could find no data on the use of an a-glucosidase inhibitor (Precose) with a DPP-IV inhibitor (Januvia), nor could I find data on the use of Januvia with an incretin mimetic such as exenatide (Byetta). In the absence of data, my response is mere conjecture. However, there are no specific contraindications to using either of these agent pairs in combination, and in the case of a Precose-Januvia combination, I would expect their effects to be additive. In theory, since Precose limits the intestinal absorption of glucose and Januvia has a glucose-dependent mechanism of action, it is plausible that Precose could blunt the efficacy of Januvia. In contrast, both Januvia and Byetta raise levels of GLP-1 but by different mechanisms, and I suspect their use together may be synergistic. In this case, Byetta would be broken down more slowly by DPP-IV once that enzyme is inhibited by Januvia.
—Daniel G. Tobin, MD (113-12)

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