| Clinical data | |
|---|---|
| Trade names | Byetta |
| AHFS/Drugs.com | monograph |
| MedlinePlus | a605034 |
| Pregnancy cat. | C |
| Legal status | ℞ Prescription only |
| Routes | subcutaneous injection |
| Pharmacokinetic data | |
| Bioavailability | N/A |
| Metabolism | proteolysis |
| Half-life | 2.4 h |
| Excretion | renal/proteolysis |
| Identifiers | |
| CAS number | 141732-76-5 |
| ATC code | A10BX04 |
| DrugBank | DB01276 |
| UNII | 9P1872D4OL |
| KEGG | D04121 |
| Chemical data | |
| Formula | C184H282N50O60S |
| Mol. mass | 4186.6 |
| (what is this?) (verify) |
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Exenatide (INN, marketed as Byetta) is a medication approved in April 2005 for the treatment of diabetes mellitus type 2. It belongs to the group of incretin mimetics and is manufactured by Amylin Pharmaceuticals and Eli Lilly and Company.
Exenatide is administered as a subcutaneous injection (under the skin) of the abdomen, thigh, or arm, any time within the 60 minutes before the first and last meal of the day.[1]
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Exenatide is a synthetic version of exendin-4, a hormone found in the saliva of the Gila monster that was first isolated by Dr. John Eng in 1992 while working at the Veterans Administration Medical Center in the Bronx, New York. It displays biological properties similar to human glucagon-like peptide-1 (GLP-1), a regulator of glucose metabolism and insulin secretion. According to the package insert, exenatide enhances glucose-dependent insulin secretion by the pancreatic beta-cell, suppresses inappropriately elevated glucagon secretion, and slows gastric emptying, although the mechanism of action is still under study.
Exenatide is a 39-amino-acid peptide, an insulin secretagogue, with glucoregulatory effects. Exenatide was approved by the FDA on April 28, 2005 for patients whose diabetes was not well-controlled on other oral medication.[2] The medication is injected subcutaneously twice per day using a filled pen device. The abdomen is a common injection site, after the area is cleaned with an alcohol pad. A new pen must first be tested to see if the medicine is flowing.
The incretin hormones GLP-1 and glucose-dependent insulinotropic peptide (GIP) are produced by the L and K endocrine cells of the intestine following ingestion of food. GLP-1 and GIP stimulate insulin secretion from the beta cells of the islets of Langerhans in the pancreas. Only GLP-1 causes insulin secretion in the diabetic state; however, GLP-1 itself is ineffective as a clinical treatment for diabetes as it has a very short half-life in vivo. Exenatide bears a 50% amino acid homology to GLP-1 and it has a longer half-life in vivo. Thus, it was tested for its ability to stimulate insulin secretion and lower blood glucose in mammals, and was found to be effective in the diabetic state. In studies on rodents, it has also been shown to increase the number of beta cells in the pancreas.
Commercially, exenatide is produced by direct chemical synthesis. Historically, exenatide was discovered as a protein naturally secreted in the saliva and concentrated in the tail of the Gila monster. While the exenatide protein was structurally analogous to GLP-1, it had a much longer half-life after injection; this enabled consideration and development of exenatide as a diabetes mellitus treatment strategy. Given this history, exenatide is sometimes referred to as "lizard spit". Subsequent clinical testing led to the discovery of the also desirable glucagon and appetite-suppressant effects.
Exenatide is approved "as adjunctive therapy to improve glycemic control in patients with type 2 diabetes mellitus who are taking metformin, a biguanide, or a combination of metformin and a sulfonylurea, but have not achieved adequate glycemic control". It has now been approved for use with thiazolidinediones such as pioglitazone or rosiglitazone.
Exenatide raises insulin levels quickly (within about ten minutes of administration) with the insulin levels subsiding substantially over the next hour or two. A dose taken after meals has a much smaller effect on blood sugar than one taken beforehand. The effects on blood sugar diminish after six to eight hours.[1] The medicine is available in two doses: 5 mcg and 10 mcg. Treatment often begins with the 5 mcg dosage, which is increased if adverse effects are not significant.[3]
According to the manufacturer, the autoinjector must be stored in a refrigerator between 2 °C (36 °F) and 8 °C (46 °F) before first use, and then at a temperature between 2 °C (36 °F) and 25 °C (77 °F). In hot weather, therefore, they should be refrigerated.[4] Pens contain sixty doses designed to be used twice a day for 30 days.
Exenatide received US Patent 5,424,286 which was filed May 24, 1993.
Exenatide is believed to facilitate glucose control in at least five ways:
In an open-label, randomized, controlled trial of 551 patients,[8] exenatide treatment for 26 weeks was associated with 2.3 kg weight loss; however, gastrointestinal symptoms were more common in the exenatide group, including nausea (57.1%), vomiting (17.4%) and diarrhea (8.5%). For most patients, the nausea is mild to moderate and goes away entirely after a few days or weeks. Medical professionals who work with exenatide have stated much of what is reported as nausea is actually a feeling of fullness. Exenatide is speculated to make most patients need to eat less, and until an adjustment is made to smaller portions, the result is the fullness feeling.
Advantages: While other treatment options share one or more of the first three characteristics, some diabetics specialists view exenatide as a significant improvement over other available diabetic medications, although most doctors do not use it as primary therapy at this time. Except for metformin and acarbose, all other available drugs for improving glucose control have been associated with weight gain.
Disadvantages: In addition to gastrointestinal adverse reactions, a relative disadvantage of exenatide is that it is administered by injection. See side effects section below.
Note: Since the major action of this drug is to enhance the release of endogenous insulin from the pancreas, exenatide is not for use in type 1 diabetes.
The main side effects of exenatide use are gastrointestinal in nature, including acid or sour stomach, belching, diarrhoea, heartburn, indigestion, nausea, and vomiting; exenatide is therefore not meant for people with severe gastrointestinal disease. Other side effects include dizziness, headache, and feeling jittery.[3] Drug interactions listed on the package insert include delayed or reduced concentrations of lovastatin, paracetamol (acetaminophen), and digoxin, although this has not been proven to alter the effectiveness of these other medications.
In response to postmarketing reports of acute pancreatitis in patients using exenatide, the FDA added a warning to the labeling of Byetta in 2007.[9][10] In August 2008, four additional deaths from pancreatitis in users of exenatide were reported to the FDA; while no definite relationship had been established, the FDA was reportedly considering additional changes to the drug's labeling.[11]
It also may increase risk of sulfonylurea-induced hypoglycemia.
Additionally, the FDA has raised concerns over exenatide raising thyroid cancer risk. The FDA delayed the decision on May 15, 2010, asking for more information from Amylin and Eli Lilly. The drug likely will be given a black box warning, the agency’s strictest caution on pharmaceuticals.[12] Eli Lilly has reported they have not seen a link in humans, but that it cannot be ruled out. Eli Lilly has admitted the drug causes an increase in thyroid problems in rats given high doses.[13]
On August 19, 2008 a Virginia man filed what is believed to be the first personal injury lawsuit stemming from injuries associated with the use of exenatide. His attorney stated "the label change in 2007 was not adequate".[14]
Eli Lilly & Co., Amylin Pharmaceuticals and Alkermes, Inc. are currently developing a long-acting release (LAR) formula of the drug, which can be injected once per week. If approved, this LAR will be marketed under the trade name Bydureon. Bydureon is tested in a Phase III clinical study program called DURATION. A cardiovascular outcomes trial (EXSCEL) has also been initiated, and will include more than 9000 patients with an estimated completion in 2017. Initial trials have shown once-weekly Bydureon provides better glycemic control than the original twice-daily injectable form, with a similar weight loss profile and lower rates of nausea.
The phase III study DURATION-1 published in 2008 showed the once weekly formulation resulted in a greater HbA1c decline and more patients reaching HbA1c targets compared to twice-daily Byetta.[15]
DURATION-2 and DURATION-3, published in 2010, showed once weekly Bydureon provided superior glycemic control and superior weight loss compared to pioglitazone (Actos), the DPP-4 inhibitor sitagliptin (Januvia) and the basal insulin glargine (Lantus).[16][17]
In October 18, 2011 National Institute for Health and Clinical Excellence (NHS) has published preliminary recommendations for using Bydureon injection weekly. The recommendations came in triple therapy regimens (in combination with metformin and a sulphonylurea, or metformin and a thiazolidinedione) and dual therapy regimens (in combination with metformin or a sulphonylurea).[18]
Scientists at the National Institutes of Health in Bethesda MD and other academic institutions are developing gene therapy based administration of Exendin-4 without the need for expensive daily injections.[19]
A research group led by Hee-Sook Jun published a paper in Diabetes indicating the delivery of GLP-1 through an adenoviral vector had a significant long term effect on diabetes.[20]
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