Pharmaceutical companies that depend completely on one drug for their success can make for some volatile investments as that single drug goes through clinical trials or its revenue potential becomes clearer. Santarus (NASDAQ:SNTS) is one of those companies. The FDA approved its Zegerid drug -- which treats frequent heartburn -- back in 2004, but with no pipeline to speak of, Santarus knows its shares rely completely on Zegerid's sales outlook.

Santarus announced its third-quarter results yesterday. With guidance calling for 2008 sales to grow to more than $200 million, the next few quarters will be pivotal in seeing whether the company can meet that goal. This quarter, sales of Zegerid grew to $12 million, compared to the $4 million earned last year, and the cost of sales was 9%. That shows the type of margins the company can achieve, if it can scale sales larger than its general corporate and marketing expenses, which totaled $25 million this quarter.

But since Zegerid loses patent protection in 2016, Santarus needs to create value for its shareholders immediately. To do that, Santarus announced this quarter that it will expand its sales force by 150 people, to bring its total to 520. The company expects that the move will drain as much as an additional $35 million in expenses annually but will help it get to breakeven earnings by the second half of 2008.

The other notable event this quarter was the deal Santarus made with Schering-Plough (NYSE:SGP) to hand over the rights for any possible over-the-counter sales of Zegerid in exchange for an initial $15 million up front, plus $65 million in milestones and an undisclosed percentage of sales as a royalty. The best part of this deal is that it will limit any future dilutive financing Santarus needs to do as it waits to achieve profitability. On the other hand, it will probably cause future operating margins to be lower than they would otherwise be if OTC sales cannibalize prescription Zegerid sales more than they expand the market for the drug.

Specialty pharma companies without a lot of moving parts -- like Santarus -- are fairly easy to analyze. Either they ramp up sales fast enough and become a juicy target for a big pharma looking for a synergistic acquisition, or their sales growth lags along with their share price. In a few quarters, investors should be able see which scenario fits Santarus.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has a disclosure policy .