Exenatide

Exenatide is an incretin mimetic of the glucagon-like peptide-1 (GLP-1) receptor agonist class, developed to treat type 2 diabetes mellitus ^[1]. It is a 39-amino-acid peptide based on exendin-4, a compound originally found in the venomous saliva of the Gila monster, a lizard native to the southwestern United States ^[1][2]. Work in the 1990s showed that exendin-4 activates the human GLP-1 receptor yet resists the rapid enzymatic breakdown that limits native GLP-1, which made it a practical basis for a medicine ^[2].

Exenatide was the first GLP-1 receptor agonist approved for type 2 diabetes, cleared in the United States in 2005 ^[1]. It was initially marketed by Amylin Pharmaceuticals and Eli Lilly as Byetta, a twice-daily subcutaneous injection, and later as Bydureon, an extended-release form given once weekly; the product line subsequently passed to AstraZeneca ^[1]. It is generally added on to oral agents such as metformin when those alone do not achieve adequate glucose control, and it is given by injection because, as a peptide, it would be digested if swallowed ^[1].

Large outcome studies have examined the drug's effects on the heart. The EXSCEL trial found that once-weekly exenatide was safe with respect to major cardiovascular events but did not significantly reduce them compared with placebo ^[3]. A broader meta-analysis of the GLP-1 receptor agonist class, which included exenatide, concluded that these drugs as a group lower the risk of major cardiovascular events, cardiovascular death and kidney complications in people with type 2 diabetes ^[4]. Compared with the longer-acting agents in its class, short-acting exenatide has a stronger effect on after-meal glucose through slowed gastric emptying and a comparatively smaller effect on fasting glucose ^[4].

Exenatide is a prescription-only medicine. Its labeling carries warnings about pancreatitis and, for the extended-release form, a boxed warning regarding thyroid C-cell tumors seen in rodents ^[1]. Common effects include nausea and injection-site reactions, and because it does not itself force insulin release when glucose is normal, hypoglycemia is uncommon unless it is combined with insulin or a sulfonylurea ^[1].

Nausea is very common, especially early on, along with vomiting and diarrhea. It carries a risk of pancreatitis, and the extended-release form carries the class thyroid C-cell tumor warning based on rodent data, so it is avoided in people with a history of medullary thyroid cancer or MEN 2. It is not recommended in severe kidney impairment since it is cleared renally.

Exenatide's main interaction mechanism is mechanical rather than metabolic. It slows gastric emptying as part of its therapeutic action, so anything swallowed alongside it reaches the small intestine later and often at a lower peak. Drugs that depend on a fast peak, oral analgesics in particular, lose effect; antibiotics and oral contraceptives show reduced Cmax. Total absorption is usually preserved, so the problem is timing rather than lost dose.

Warfarin was studied directly. A crossover study in healthy men found exenatide produced no significant change in R or S warfarin pharmacokinetics and only a minor reduction in anticoagulant effect, which the investigators judged not to be a safety concern. Postmarketing reports of raised INR with bleeding exist, so the pairing is still watched.

Exenatide rarely causes hypoglycaemia by itself, since its insulinotropic effect is glucose dependent. Combined with a sulfonylurea or with insulin, though, the risk of clinically significant hypoglycaemia rises substantially, and that combination accounts for most exenatide associated hypoglycaemia.

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