Volume 111, Issue s21

Incretin-based therapies (subcutaneously administered glucagon-like peptide-1 [GLP-1] agonists and oral dipeptidyl peptidase-4 inhibitors) represent a new mechanism of action with which to target the adverse effects of type 2 diabetes mellitus. Both classes of incretins are excellent choices for patients who have jobs that do not permit use of insulin therapy, who have hypoglycemic unawareness, or for whom hypoglycemia is an especially worrisome potential adverse effect. Glucagon-like peptide-1 agonists are an attractive choice for patients in whom promotion of weight loss is a major consideration and the glycated hemoglobin level is moderately elevated (<8.0%) (ie, insulin is not required). Short-acting exenatide has been available since 2005 and is administered twice a day before meals. Liraglutide is the first of the long-acting GLP-1 agonists to be approved in the United States and is administered once a day. The most common adverse effects of GLP-1 agonists are those related to the gastrointestinal system. Both exenatide and liraglutide are associated with weight loss when used as monotherapy or as part of combination-therapy strategies. Glucagon-like peptide-1 agonists also have beneficial effects on cardiovascular risk factors such as blood pressure and lipids.

The pathophysiology of type 2 diabetes mellitus is complex, consisting of far more physiologic defects than simple insulin resistance and β-cell dysfunction. Our understanding of this progressive disease has moved from a “dual defect” to an “ominous octet” description. This multifactoral concept may explain the difficulty in achieving and maintaining glycemic goals with traditional therapies. Glucagon-like peptide-1 (GLP-1) agonists, which improve insulin secretion, decrease glucagon secretion, increase satiety (and therefore decrease food intake), and may have beneficial effects on β-cell function, represent an important addition to treatment options. Their glucose-dependent mechanism limits the risk for hypoglycemia, and they are associated with weight loss. Glucagon-like peptide-1 agonists may be used alone in patients intolerant of metformin or in combination with metformin, thiazolidinediones, and sulfonylureas (or in any combination therereof). Concomitant use of dipeptidyl-peptidase-4 inhibitors is not recommended because they have a similar basis of action. Current US Food and Drug Administration indications do not include the concomitant use of GLP-1 agonists with insulin.

The management of type 2 diabetes mellitus and, in particular, blood glucose levels can be complex and challenging for physicians and patients. Many patients are frustrated with the agents currently available because they have associated limitations of weight gain, hypoglycemia, and tolerability issues. Advantages of glucagon-like peptide-1 (GLP-1) agonists include their efficacy in lowering blood glucose levels, their lack of association with weight gain, and their indirect association with weight loss. Patients likely to benefit from GLP-1 agonist therapy are those in the early stages of the disease and those in need of sufficient benefit from an agent with good efficacy. Setting appropriate expectations for patients is important, as well as explaining the significance of glucose control and reminding patients that this is the main goal of therapy. Patients (and physicians) who have concerns about hypoglycemia can be reassured that GLP-1 agonists work only in the presence of hyperglycemia. Longer-acting GLP-1 agonists are dosed less frequently, appear to be associated with less nausea, and may be associated with better rates of adherence than shorter-acting agents. When initiating therapy with GLP-1 agonists, doses should be gradually escalated to minimize gastrointestinal adverse effects. The dose of a sulfonylurea may need to be lowered if a GLP-1 agonist is added. A review of possible adverse effects, contraindications, dosing and administration techniques, and expected benefits of therapy is provided in the present article to optimize success rates with this new class of agents.