Shares of Arena Pharmaceuticals (ARNA) soared last Friday after the company announced an amended marketing agreement with Eisai for the company's obesity drug Belviq. This expanded marketing agreement gives Eisai exclusive commercialization rights for Belviq in all countries except South Korea, Taiwan, Australia, and New Zealand.

Per the agreement, Arena will receive $60 million in upfront payments, up to $176.5 million in regulatory and development milestone payments, and $1.56 billion in one-time purchase price adjustment agreements in the newly covered territories.

This expanded deal couldn't come at a better time for Arena investors. To date, Belviq's U.S. launch has been slow by industry standards, with Arena only generating $1.7 million in revenue from the drug in the third quarter. Orexigen Therapeutics (NASDAQ: OREX) is also hot on Arena's heels in the development of its competing obesity drug Contrave, with possible approvals coming next year in both the U.S. and Europe.

Perhaps the only good news on the commercial front for Arena of late has been VIVUS' (VVUS) problematic launch of Qsymia. Since last July, First Manhattan has essentially taken over the board of directors in an attempt to turn the company around and improve Qsymia sales. Even so, this turnaround effort has resulted in three different CEOs in less than two months, making it hard for VIVUS to implement its new marketing strategy for Qsymia.

Looking past the expanded marketing agreement
I believe Foolish investors should look past the newly minted marketing deal with Eisai, and dig a bit deeper into Arena's recent conference call. While the marketing agreement made headlines, the conference call contained a number of important tidbits that investors should pay attention to going forward.

Key takeaways from the conference call
First off, Arena management noted that more than 10,000 doctors have now prescribed Belviq, showing that Eisai's education efforts are paying dividends. As further proof that doctors and patients are taking interest in the drug, management pointed out that traffic to Belviq's website is increasing at a steady rate.

Another key takeaway that got lost in the excitement of the amended marketing agreement is that major private insurers are starting to include Belviq in their coverage. Insurance coverage for obesity meds has long been a problem in the industry. So this apparent change of heart should help boost Belviq sales going forward.

On the clinical front, management noted that an initial fixed dose pilot study with phentermine has been completed, and a larger pilot study for the Belviq-phentermine combo will be performed soon. Arena also completed studies on the long-awaited once-daily, extended-release formulation of Belviq, and mid-stage trials to expand Belviq's label for diabetes and smoking cessation are in the works. Finally, management also championed the significant progress of their other early stage clinical candidates, with multiple mid-stage trials planned for early 2014.

A Fool's outlook
So, while the amended marketing agreement is certainly important, the recent conference call shows there are a number of reasons to keep a close watch on Arena. I find it particularly interesting that CEO Jack Lief explicitly stated that the company choose Eisai as a global marketing partner because he believes Eisai gives Arena the best chance of expanding Belviq's label.

With sales of both Belviq and Qsymia struggling to gain traction in the obesity sector, an expanded label may be crucial to Belviq's commercial success. And potential competition from Contrave next year won't help the situation.

What's my outlook on Arena? I personally think it's best to stand on the sidelines for now. I want to see how Eisai's continued education efforts play out at upcoming medical and investor conferences before making a call. With the CEO even sounding like he believes the real value of Belviq lies in expanding the label, it might take a while for the drug's true value to be unlocked. I plan to keep Arena on my radar as the plan to expand Belviq's label unfolds.