Any drugmaker bold enough to test one of its drug candidates directly against a competitor dramatically increases that compound's risk of failure. On Friday, Novo Nordisk (NYSE:NVO) seems to have cleared this lofty hurdle, delivering promising results for a potential blockbuster diabetes compound.

Testing a drug in development against an already approved competitor is always tougher than a traditional placebo-controlled study. Not only must the compound show that it is effective and relatively safe, but it must also prove itself at least as effective as the rival drug. Novo Nordisk tested its type 2 diabetes GLP-1 analogue treatment liraglutide in a phase 3 study against Eli Lilly (NYSE:LLY) and Amylin Pharmaceuticals' (NASDAQ:AMLN) already-approved GLP-1 analogue Byetta.

Patients treated with liraglutide saw their blood sugar levels reduced by "more than 1.1 percentage points" with liraglutide, versus "less than 0.8 percentage points" with Byetta. This is the most commonly used efficacy endpoint in any diabetes study, and the gold standard used in evaluating such treatments by the FDA and other medical authorities worldwide.

Although I'm not calling this anything close to definitive yet, liraglutide also appears to have bested Byetta on safety issues common to the two drugs, including nausea and minor hypoglycemia. In addition, diabetics only need to inject themselves with liraglutide once a day, compared to Byetta's twice-a-day dosing. Assuming that Novo Nordisk's study was well-balanced, it looks like liraglutide trounced Byetta across the board on efficacy, convenience, and possibly safety.

Lilly and Amylin do have a long-acting once-a-week version of Byetta, designed using Alkermes' (NASDAQ:ALKS) extended-release technology, but it won't be submitted to the FDA until next year. Other drugmakers like MannKind (NASDAQ:MNKD) have also done work on developing rival GLP-1 analogues. That said, this space now seems like Novo's to lose, if liraglutide can get onto the market. These promising results provide yet another reason to like Novo Nordisk.

More Foolishness to get your blood sugar up: