NEWTON, Mass. ( TheStreet) -- Clinical Data ( CLDA) scored a big victory with the approval of a new antidepressant, sending the stock price soaring 68% to $25.17 on Monday. Many of the company's shareholders and supporters, however, are looking for an even bigger payday when Clinical Data sells itself to the highest bidder.

A sale of Clinical Data is seen as an obvious and inevitable next step, many current shareholders believe, because the company's new antidepressant Viibryd is a $2-3 billion-a-year blockbuster that will prove irresistible to any of the large pharmaceutical firms desperate for new growth.

Clinical Data bulls are doubly confident in a sale because they have Randall J. Kirk on their side of the negotiating table. Kirk, Clinical Data's chairman and largest shareholder with a 37% stake, is known as a consummate dealmaker. He became a billionaire after selling New River Pharmaceuticals to Shire ( SHPGY) for $2.6 billion in 2007, but previous to that, he had a hand in Johnson & Johnson's ( JNJ) $2.3 billion purchase of Scios in 2003.

At Monday's close and using a fully diluted share count, Clinical Data is worth over $1 billion already even with Viibryd still three or four months away from a commercial launch. Yet, bulls like Wedbush Securities analyst Greg Wade believe the company could be bought for upwards of $2 billion, or $40-plus per share. An institutional investor in Clinical Data who asked to remain anonymous believes Clinical Data is worth more, perhaps as much as $60 a share.

Nonsense, say Clinical Data bears, including short sellers who initiated positions Monday on the stock's run-up following Viibryd's approval. To the bear's eye, Viibryd is me-too antidepressant with tolerability issues of its own. Sure, the $12 billion U.S. antidepressant marketing is attractive but cheap generics are grabbing a larger share of the market and insurers will throw reimbursement roadblocks in Viibryd's way. Clinical Data will be lucky to do $300 million in peak Viibryd sales, the bears say.

And while Kirk's money-making M&A track record is undeniable, bears say Shire was an obvious and desperate buyer for New River. With Viibryd, Kirk faces a tougher challenge and no obvious or desperate buyers. This makes Clinical Data look more like Savient Pharmaceuticals ( SVNT) or Vanda Pharmaceuticals ( VNDA) -- two small drug companies with stocks that spiked on drug approvals only to fall sharply in the following weeks and months. The former couldn't find a buyer and was forced to sell its gout drug solo; the latter found a partner, Novartis, to market its schizophrenia drug but so far, hardly anyone is prescribing it.

"This Clinical Data is a gift. I wasn't short into the PDUFA thankfully, but I shorted the heck out of it this morning," said one hedge fund manager to me Monday. "They're not going to sell Bleep. "

The Clinical Data bulls won round one against the shorts with Viibryd's approval, but now the fight moves to round two. A closer look at the bull and bear cases for Clinical Data now that Viibryd is approved:

Clinical Data CEO Drew Fromkin isn't guaranteeing a sale of the company but on a Monday conference call and in a subsequent interview, he acknowledged that preliminary discussions with potential buyers and partners have already been held and will continue even as the company moves ahead with the Viibryd launch on its own. The American Psychiatry Association Annual Meeting, May 14-18, could be a key coming-out event for Viibryd.

"I think when you look at the number of new molecular entities, especially in a market of this size being approved is so little, this is a tremendous opportunity for us and a tremendous opportunity for another party," said Fromkin. "And we expect to explore that. But in no way will we waver from our position to be able to launch this product in the next three or four months."

Based on clinical data and comparisons with data generated by older antidepressants, Viibryd's efficacy is on par, perhaps slightly lower, than the many of the other drugs in the antidepressant class. Clinical Data's Fromkin points out that Viibryd's dual mechanism of action means patients may respond differently to Viibryd than they do to other currently marketed antidepressants. Viibryd has not been compared directly against other antidepressants in clinical studies, but Fromkin says Viibryd's label describes a drug that is safe and well tolerated and compares very well to other antidepressants, he adds.

Diarhea, nausea and vomiting were the most commonly reported adverse events in the Viibryd phase III studies but none resulted in more than 1% of patients discontinuing the drug. Overall, only 7% of Viibryd patients discontinued due to an adverse event compared to 3% of placebo patients. Importantly, Viibryd caused no weight gain and minimal sexual side effects. Decreased libido, erectile dysfunction, ejaculation disorder or problems reaching orgasm, were reported by low single-digit percentages of patients on Viibryd.

"By contrast, sexual dysfunction is a major problem with the SSRIs," notes Fromkin, referring to the select serotonin reuptake inhibitor class of antidepressants, which includes Forest Labs' ( FRX) Lexapro.

Viibryd has patent protection in the U.S. through 2019 and possibly as long as 2022.

Wedbush's Wade estimates peak Viibryd sales of more than $2 billion seven years after launch, which represents just 7% to 8% penetration in the overall antidepressant drug market. He thinks a Clinical Data buyout is a real possibility but also believes the company can successfully launch Viibryd on its own and reach break even or a cash-flow positive state within 12 months of a launch.

"I think there's an absence of respect on the Street for what Clinical Data has achieved so far with Viibryd," says Wade.

Potential buyers of Clinical Data include Forest Labs, which just suffered a setback with its own antidepressant in a phase III study, GlaxoSmithKline ( GSK), Pfizer ( PFE), or Eli Lilly ( LLY).

Clinical Data bears downplay Viibryd's "safe and well tolerated" profile, pointing to the 28% rate of diarrhea and 23% rate of nausea observed in the phase III studies as a real tolerability problem for patients. Viibryd's efficacy -- no better or slightly worse than currently marketed antidepressants -- doesn't help either.

One short seller of Clinical Data joked to me that the almost one-third of patients on Viibryd who are suffering from diarrhea are not having sex, which undermines the company's message that Viibryd doesn't impede sexual activity like other antidepressants.

Patients are also required to titrate to a full Viibryd dose over two weeks, which makes taking the drug more of a hassle than other antidepressants that can be taken immediately at full dose.

The biggest impediment to Viibryd's success, bears say, is the competitive antidepressant market itself. While bulls cite $12 billion a year in antidepressant sales, that encompasses broader indications like acute, maintenance and refractory treatment of depression for which Viibryd does not qualify because of a lack of clinical data. In essence, Viibryd, with data from just two, short clinical trials against a placebo, will be considered for a far smaller patient population.

And within that smaller patient population of people suffering from depression, many treatment options already exist, including lower-priced generics.

"In the tough reimbursement environment of 2011, Viibryd is the end-of-the-line choice for patients with major depressive disorder," said another Clinical Data short who believes the drug rakes in a fraction of the sales predicted by the bulls.

"Clinical Data has been for sale for months already but has not been able to close a deal because the Big Pharma guys don't have interest in selling another me-too antidepressant," the short seller adds.

Summing up the short thesis: Clinical Data is more than likely to launch Viibryd on its own or under a less-than-ideal marketing partnership agreement this spring. If that happens, bulls will be worried that there is no buyer for the company and the stock will take a big hit.

Selling a new drug in a competitive market is tough for anyone but especially for a smaller company, which puts Clinical Data in the same unenviable position as companies like Allos Therapeutics ( ALTH), Somaxon Pharmaceuticals ( SOMX), Savient and Acorda Therapeutics ( ACOR) which have all suffered stock market falls following drug approvals.

--Written by Adam Feuerstein in Boston.

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