KKR & Co. LLP (KKR - Get Report) -backed Arbor Pharmaceuticals LLC and Purdue Pharmaceutical Products LP could be among interested buyers as DepoMed Inc.  (DEPO) hits the block after resisting a hostile takeover.

Although the pharmaceutical firm that rebuffed takeover attempts by Horizon Pharma plc (HZNP - Get Report) just last year and is now exploring a sale has solid growth prospects, its main pain medication drug, an opioid known as Nucynta, accounts for more than 60% of its sales and is subject to both a patent dispute and closer regulatory oversight. 

The move to put itself up for bids, which Reuters broke late Thursday, comes in response to activist investor Starboard Value LP's Jeff Smith deal-related agitations at the company. Starboard disclosed a 6.8% activist stake at DepoMed in April, shortly after it had defeated the hostile bid by Horizon Pharmaceuticals.

Starboard said Monday it delivered a letter to the board of Depomed seeking a special shareholder meeting for Nov. 15. The company, which has a 9.8% stake in Depomed, said Depomed needs to replace its board. Starboard faced a Friday deadline to call a special shareholder meeting. 

"Starboard has made it perfectly clear that if they get control of the company, they're more likely to sell it," analyst Chiara Russo of Cantor Fitzgerald said in an interview.

The activist fund challenged the company on its plans to shift its legal domicile from California to Delaware. The re-incorporation move would have allowed DepoMed to prohibit shareholders from calling a special shareholder meeting to elect dissident directors, but the pharmaceutical company cancelled the reincorporation plan in April.

After that, Starboard, a prolific employer of proxy fights to elect directors at annual and special meetings, launched efforts to call a special shareholder meeting to replace the entire board of directors with its dissident slate of nominees.

Most recently, in July, Starboard announced it had appointed two pharmaceutical executives as advisers. Starboard often hires advisers who provide sector expertise about the target company's industry. The advisers are potential candidates to become dissident director candidates for the activist fund.

And DepoMed is not the only drug company Starboard has targeted after it rejected an unsolicited bid. The activist fund is in the midst of a campaign it launched at Perrigo Co. (PRGO - Get Report) earlier this month that came after the drug company fought back a hostile bid from generics giant Mylan Inc.  (MYL - Get Report) last year.

"Depo being bought has been talked about ad nauseum since Starboard came into the picture," Russo said. "Every name has been thrown out there as a buyer."

Much depends on a patent dispute in the United States District Court of New Jersey over Nucynta, which will be decided by the end of this month. Whether or not the company is an attractive target hinges on this lawsuit, analysts say, as does a fair purchase price.

As long as its patent suit is cleared up, DepoMed is likely to be an attractive target. Although it's rare in the pharmaceutical space for a mid-cap company to have products both in development and for sale, the company is obviously heavily dependent on Nucynta. 

"It's difficult to find a surviving billion dollar drug company that's doing it on their own with multiple products," Russo said.

DepoMed, which is based in Newark, Calif., focuses on drugs for pain and the central nervous system. Besides chronic pain drug Nucynta, the company markets post-shingles pain drug Gralise, migraine relief medication Cambia, nasal spray for cancer pain Lazanda and arthritis pain medication Zipsor. It also has several drugs in development.

But given DepoMed's dependence on Nucynta, which it acquired in Jan. 2015, it might be better off as part of a company with a more diverse portfolio.

According to analyst Ken Trbovich of Janney Montgomery Scott LLC, DepoMed would fit especially well into Arbor Pharmaceuticals. Trbovich said he has a hunch that Arbor made a bid for DepoMed in the 2015 auction process. Arbor could not be reached to confirm this.

"They couldn't justify the premium because of the unresolved nature of patent filings," Trbovich said of the 2015 auction in an interview. "Timing wise it would make sense that they would have an interest in the company at this point, given the Sept. 30 deadline."

Another potential buyer tossed around by analysts is Purdue Pharmaceutical Products. The company has pending patent litigation against DepoMed over another of it's drugs that could easily be cleared up if it decided to buy DepoMed, both analysts noted.

"From our point of view there's a reason why strategically Purdue would have an interest," Trbovich said in an interview. "Nucynta gives them an opportunity to have a second product in the [oxytocin] category."

Russo said that she didn't think another bid from Horizon was likely, thanks mostly to the company's recent $800 million all-cash acquisition of Raptor Pharmaceutical Corp. (RPTP) , which was announced last week.

Endo Pharmaceuticals plc (ENDP - Get Report) was another name tossed around, although Russo said the company has recently refocused, pledging to focus on organic growth, and likely won't be looking to do more deals soon.

According to Trbovich, a purchase price of $28 per share, or $31.3 million based on shares outstanding, is likely for DepoMed.

Russo said the price could go up to $41.4 million, or $37 per share under certain circumstances, although she conceded that this price was likely a bit high.

According to Trbovich, the FDA has indicated that it may create financial incentives to promote abuse deterrent opioids, which are competitors to DepoMed's drugs. The FDA may also try to have those that are non-abuse deterrent removed from the market, Trbovich noted.

DepoMed closed Friday trading at $24.34 per share, up 14.6% from market's open. Shares ticked up 16 cents Monday.

EDITORS' NOTE: This article has updated to reflect Starboard's statements Monday.