Januvia hit our shelves this past week, and I marveled at how inexpensive it was for a brand new drug. (~$300, if dim memory serves.) I think Merck’s going to have a runaway hit on their hands, and Amylin and Lilly are going to be the ones that lose out. I almost feel like I’m stating the obvious here — heck, maybe I am, I haven’t kept with any business news and speculation in several months.

Exenatide (Byetta) is a glucagon-like peptide analog that responds to glucose by stimulating insulin release and inhibiting glucagon release. It also slows gastric emptying, inhibits synthesis of glucagon, and stimulates beta cell neogenesis by preventing beta cell death. It only responds in the presence of glucose, which means there’s low risk for hypoglycemia.

Unfortunately, GLP-1 is broken down by DPP-IV, which limits native GLP-1 half-life to about 90 seconds. GLP-1 is also efficiently cleared by the kidneys. The other downside to Byetta is the fact that it’s injected.

Sitagliptin (Januvia) prevents the breakdown of the body’s own GLP-1 (and other incretin hormones) by inhibiting DPP-IV. As an oral tablet, patient compliance is likely to be higher, or at the very least, it’s more convenient than poking oneself.

Despite having entirely different mechanisms of action, the net effect is the same: higher levels of GLP-1 in the body, with low risk of hypoglycemia. Both Byetta and Januvia are likely to help patients lose weight as well. There’s been some talk about possibly getting Byetta approved as a weight-loss drug — I don’t know how far along this idea is, however.

It’s only a matter of time before we start getting insurance rejections for prior authorizations telling us that the doctor needs to try Januvia before they’ll approve Byetta. This is good news for those seniors on Medicare Part D plans as well — Januvia can save them a pile of money because it’s just so much cheaper than Byetta.

So to recap:

• Easier to store (no refrigeration)
• Oral tablet vs injection
• Once a day dosing instead of twice a day poking
• Cheaper

I think all the pieces are in place for Merck is going to eat Eli Lilly and Amylin’s lunch here. It seems one investment house is also predicting something similar. (PDF)