View the Table: GLP-1 and GIP/GLP-1 Receptor Agonists for Type 2 Diabetes

The injectable glucagon-like peptide-1 (GLP-1) receptor agonist semaglutide (Wegovy) has been approved by the FDA to reduce the risk of major adverse cardiovascular events (MACE) in adults with established cardiovascular disease (CVD) and either obesity or overweight. Semaglutide is the first drug to be approved for cardiovascular risk reduction in this population. It is also approved in a lower-dose injectable formulation as Ozempic and in an oral formulation as Rybelsus (see Table 1).

Glucagon-like peptide-1 (GLP-1) receptor agonists and the dual glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 receptor agonist tirzepatide (Mounjaro) are widely prescribed for treatment of type 2 diabetes and weight management (see Table 1), but they delay gastric emptying and commonly cause nausea and vomiting. Gastroparesis and bowel obstruction (ileus) have also been reported with their use.

The sodium-glucose cotransporter 2 (SGLT2) inhibitor empagliflozin has been available for years alone (Jardiance – Boehringer Ingelheim) and in combination with metformin (Synjardy) to improve glycemic control in adults with type 2 diabetes. Both products have now been approved for use in children ≥10 years old. Empagliflozin is the second oral drug to become available in the US for treatment of type 2 diabetes in children; metformin has been available since 2000 for this indication. The injectable glucagon-like peptide-1 (GLP-1) receptor agonists liraglutide (Victoza) and extended-release exenatide (Bydureon BCise) are also approved for use in children ≥10 years old.

Diet, exercise, and weight loss can improve glycemic control, but almost all patients with type 2 diabetes require antihyperglycemic drug therapy. Treating to a target A1C of <7% while minimizing hypoglycemia is recommended to prevent microvascular complications of diabetes (retinopathy, nephropathy, and neuropathy). An A1C target of <8% may be appropriate for some older patients.

Diet, exercise, and weight loss can improve glycemic control, but almost all patients with type 2 diabetes eventually require drug therapy. Treating to a glycated hemoglobin (A1C) concentration of <7% can prevent microvascular complications (retinopathy, nephropathy, and neuropathy), but whether it prevents macrovascular complications and death is unclear. An A1C target of <8% may be appropriate for older patients and those with underlying cardiovascular disease (CVD), a history of severe hypoglycemia, diabetes-related complications, a limited life expectancy, or a long duration of disease.

An oral formulation of the glucagon-like peptide-1 (GLP-1) receptor agonist semaglutide (Rybelsus – Novo Nordisk) has been approved by the FDA for once-daily treatment of type 2 diabetes in adults. Semaglutide, which has been available in a subcutaneously-injected formulation (Ozempic) since 2017, is the first GLP-1 receptor agonist to become available for oral administration; the 4 other GLP-1 receptor agonists currently available in the US are administered by subcutaneous (SC) injection.

Since 2008, because of safety concerns, the FDA has mandated that long-term cardiovascular outcomes trials be conducted for all new drugs for type 2 diabetes. Reductions in the incidence of macrovascular complications in these trials with some sodium-glucose co-transporter 2 (SGLT2) inhibitors and glucagon-like peptide 1 (GLP-1) receptor agonists in patients at risk for cardiovascular disease (see Table 1) have led to new recommendations.

The FDA has approved semaglutide (Ozempic – Novo Nordisk), a long-acting injectable GLP-1 (glucagon-like peptide-1) receptor agonist, for once-weekly treatment of adults with type 2 diabetes. It is the sixth GLP-1 receptor agonist to be approved in the US.

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For many years, the goal of drug therapy for most patients with type 2 diabetes has been to achieve and maintain an A1C of <7%. Achieving that goal can prevent microvascular complications (diabetic retinopathy, nephropathy, neuropathy), but whether it prevents macrovascular complications (myocardial infarction [MI], stroke) has been less clear. The FDA now requires that cardiovascular safety studies be performed for all new drugs for type 2 diabetes.1 Recent findings that some of the newer second-line drugs for type 2 diabetes have cardiovascular benefits have led to new interest in the cardiovascular efficacy and safety of all antidiabetic drugs.

The FDA has approved lixisenatide (Sanofi), a short-acting injectable GLP-1 (glucagon-like peptide-1) receptor agonist, for once-daily treatment of adults with type 2 diabetes, both alone (Adlyxin) and in a fixed-ratio combination with insulin glargine (Soliqua 100/33). Lixisenatide has been available since 2013 in many other countries as Lyxumia. It is the fifth GLP-1 receptor agonist to be approved in the US.

The goal of drug therapy for type 2 diabetes is to achieve and maintain a near-normal glycated hemoglobin (A1C) concentration without inducing hypoglycemia; the target is generally an A1C of ≤7%. Treating to this target has been shown to prevent microvascular complications (retinopathy, nephropathy, and neuropathy), but whether it prevents macrovascular outcomes is unclear. An A1C target of <8% may be appropriate for older patients and those with underlying cardiovascular disease, a history of severe hypoglycemia, diabetes-related complications or comorbidities, or a long duration of disease.

Adults with a body mass index (BMI) between 25 and 29.9 kg/m² are considered overweight. Those with a BMI ≥30 are considered obese. Losing even a small amount of weight and increasing physical activity can prevent some of the complications of obesity, particularly type 2 diabetes. Diet and exercise are the preferred methods for losing weight, but long-term failure rates are high. Several drugs have been approved by the FDA for weight reduction, but adherence is poor, adverse effects are common, and patients usually regain the lost weight when the drug is stopped. Bariatric surgery can produce substantial weight loss and significantly reduce obesity-related comorbidities; long-term data on its safety are encouraging, but still limited. Guidelines for the management of overweight or obese adults have recently been published.

Two new injectable GLP-1 (glucagon-like peptide-1) receptor agonists, dulaglutide (Trulicity [trū li si tee] – Lilly) and albiglutide (Tanzeum [tan' zee um] – GSK), have been approved by the FDA for once-weekly treatment of type 2 diabetes. Other available GLP-1 receptor agonists include exenatide, which is approved for injection twice daily (Byetta) or once weekly (Bydureon), and liraglutide (Victoza), which is injected once daily.

The goal of drug therapy for type 2 diabetes is to achieve and maintain a near-normal A1C concentration without inducing hypoglycemia; the target is generally an A1C of <7.0%. Treating to this target has been shown to prevent the microvascular complications of retinopathy and nephropathy, but whether it prevents macrovascular outcomes remains unclear. Three large trials found that intensive glucose control did not reduce the incidence of macrovascular events. One of these trials (ACCORD) in >10,000 patients with type 2 diabetes, with or at high-risk for cardiovascular disease, found that treating patients intensively with antihyperglycemic drugs to an A1C target of 6.0% for a mean of 3.7 years did not significantly reduce the incidence of major cardiovascular events (the primary endpoint) and was associated with increased all-cause mortality compared to patients treated to an A1C target of 7.0-7.9%. An A1C target of 7-8% may be prudent in older patients and in those with underlying cardiovascular disease, severe hypoglycemia, or multiple diabetes-related complications or co-morbidities.

Canagliflozin (kan" a gli floe' zin; Invokana – Janssen), a sodium-glucose co-transporter 2 (SGLT2) inhibitor, has been approved by the FDA for oral treatment of type 2 diabetes.

Most experts agree that lifestyle modifications and metformin (Glucophage, and others) should be used first to treat patients with type 2 diabetes. If metformin alone fails to control hyperglycemia, there is no general agreement on which drug should be added next. A recent article in The Medical Letter offered some support for a sulfonylurea. Three recent trials published in The Lancet favored the long-acting basal insulin glargine, the glucagon-like peptide (GLP-1) analog exenatide, and the dipeptidyl peptidase-4 (DPP-4) inhibitor linagliptin, respectively. Some of the advantages and disadvantages of these and other available agents are listed in Table 1 on the opposite page.

The FDA has approved a once-weekly extendedrelease formulation of exenatide (Bydureon – Amylin), an injectable glucagon-like peptide-1 (GLP-1) receptor agonist, for treatment of type 2 diabetes.

The development of hyperglycemia in type 2 diabetes results from a combination of metabolic abnormalities that includes insulin resistance, diminished insulin secretion and excess hepatic glucose production. Diet, exercise and weight loss are helpful in improving glucose control, but most patients ultimately require drug therapy.

Adults with a body mass index (BMI=kg/m²) of 25-<30 are considered overweight; those with a BMI of ≥30 are considered obese.

Liraglutide (Victoza – Novo Nordisk), a glucagon-like peptide-1 (GLP-1) receptor agonist given by subcutaneous injection, has been approved by the FDA for treatment of patients with type 2 diabetes. It can be used alone or in addition to oral antidiabetic drugs such as metformin (Glucophage, and others) or glimepiride (Amaryl, and others). Liraglutide is not recommended for first-line therapy and is not approved for use with insulin.

The FDA has issued an update (August 18, 2008; www.fda.gov) on occurrences of acute pancreatitis in patients with diabetes taking exenatide (Byetta – Amylin/Lilly). The latest update, which follows an FDA Alert in October 2007, reports 6 cases of hemorrhagic or necrotizing pancreatitis with 2 deaths in patients taking the drug. Whether pancreatitis occurs more often in patients taking exenatide than in patients with diabetes not taking exenatide is not clear.1

Given by subcutaneous injection, exenatide is a synthetic peptide that stimulates release of insulin from pancreatic beta cells.2 It is FDA-approved as adjunctive therapy in patients with type 2 diabetes. In addition to potentiating insulin release, exenatide slows gastric emptying, which may cause nausea and sometimes vomiting. The presenting symptoms of acute pancreatitis typically are nausea, vomiting and severe upper abdominal pain. Severe abdominal pain is not a usual side effect of exenatide. If pancreatitis is suspected in a patient taking exenatide, the drug should be discontinued promptly, and should not be restarted after recovery.

1. SR Ahmad and J Swann. Exenatide and rare adverse events. N Engl J Med 2008; 358:1970.
2. Exenatide (Byetta) for type 2 diabetes. Med Lett Drugs Ther 2005; 47:45.

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The development of hyperglycemia in type 2 diabetes results from a combination of metabolic abnormalities including insulin resistance, diminished insulin secretion and excess hepatic glucose production. Diet, exercise and weight loss are helpful in improving glucose control, but most patients ultimately require drug therapy.

Losing even a small amount of weight and increasing physical activity can prevent some of the complications of obesity, particularly type 2 diabetes. Diet and exercise are the preferred methods for losing weight but are associated with high long-term failure rates. Drugs may help some patients, but all currently available drugs for weight reduction have drawbacks. Gastric surgery can produce marked weight loss in the severely obese, but long-term data on safety are limited.

Patients may be asking about reports in the lay press that exenatide (Byetta - Med Lett Drugs Ther 2005; 47:45), a synthetic peptide that stimulates release of insulin from pancreatic beta cells, has been used by diabetics and non-diabetics to lose weight. Approved by the FDA to improve glycemic control in patients with type 2 diabetes not controlled by metformin, a sulfonylurea or both, it is given by subcutaneous injection before the morning and evening meals. In clinical trials, some diabetic patients treated with the drug lost weight. No data are available on use in non-diabetics. Exenatide slows gastric emptying and promotes satiety, which is presumably the mechanism of weight loss.

Patients should be warned that exenatide has some adverse effects. Hypoglycemia has occurred when the drug was added to a sulfonylurea but not when it was added to metformin. The risk of hypoglycemia in non-diabetics is unknown. Exenatide often causes nausea, which can be severe, and vomiting. Diarrhea can also occur. Because the drug slows gastric emptying, it can decrease the rate and extent of absorption of other drugs such as antibiotics and oral contraceptives; oral drugs should be taken at least one hour before exenatide.

Perhaps the greatest concern with off-label use of exenatide for weight loss is that 3 times the human dose given to pregnant animals slowed fetal growth and produced skeletal and other developmental abnormalities. The FDA classified it as category C (risk cannot be ruled out) for use during pregnancy. For diabetics and non-diabetics, pregnant or not, exenatide's long-term safety is unknown.

The development of hyperglycemia in type 2 diabetes results from a combination of metabolic abnormalities including insulin resistance, excess hepatic glucose production and diminished insulin secretion. In many patients, diet and regular exercise can improve glucose control. Most drugs currently available for management of type 2 diabetes increase insulin supply (sulfonylureas, other secretagogues and insulin itself), decrease insulin resistance (thiazolidinediones) or improve the effectiveness of insulin (biguanides). Alpha-glucosidase inhibitors reduce the rate of glucose absorption. Newer agents such as pramlintide (Symlin) and exenatide (Byetta) have multiple effects to increase satiety and reduce postprandial hyperglycemia.

Exenatide injection (Byetta - Amylin/Lilly), a synthetic peptide that stimulates release of insulin from pancreatic beta cells, has been approved by the FDA as adjunctive therapy for patients with type 2 diabetes who have not achieved optimal glycemic control on metformin (Glucophage, and others), a sulfonylurea, such as glyburide (DiaBeta, and others), or both. Exenatide is not indicated for use with insulin.