The cardiovascular drug candidate Pozen (Nasdaq: POZN) is developing is getting more regulatory heartache as the U.S. Food and Drug Administration is now asking the drug developer for more clinical testing on the compound.

The Chapel Hill drug developer disclosed that the regulatory agency wants more information on PA32540, an aspirin combination drug developed to deliver the cardiovascular benefits of aspirin in a way less likely to cause stomach irritation characteristic of aspirin alone. PA32540 pairs delayed-release aspirin at a 325 mg dose with the stomach acid reducer omeprazole.

In April, Pozen disclosed that the FDA suggested that the company also seek drug approval at the 81 mg dose level due to concerns that doctors may need another dose at a lower level.

In cardiovascular applications, aspirin is currently dosed at 81 mgs or 162 mgs for most indications.

At that time the FDA suggested that without approval at the additional lower dose, the agency might limit PA32540’s approval to use only in patients who have had coronary artery bypass graft, or CABG, surgery. CABG patients represent a large market but it’s a considerably smaller than Pozen’s targeted market of secondary prevention of cardiovascular disease.

In Pozen’s latest disclosure, the company said that the FDA told the company that to develop a combination drug with 81 mg aspirin, the agency needs another clinical study to determine bioequivalence – whehter the drug is the same as aspirin at the 81 mg dose. That study will be necessary unless the company can justify getting a waiver. Pozen said it plans a follow-up call with the FDA in the next few weeks to determine the next steps and its impact on filing a new drug application for the compound.

If Pozen must do new tests, it has the money to do so.

The company last year sold most of the future royalty and milestone payments of migraine drug Treximet to Canadian pension fund CPPIB Investment for $75 million. Treximet, commercialized through a partnership with GlaxoSmithKline, brought Pozen $12.2 million in royalties in 2011. But Pozen had planned to apply the money raised from selling the Treximet rights toward commercialization of PA32540, not further clinical testing.

Pozen has also been actively seeking a partner who could commercialize the drug globally. While Pozen initially planned to make PA32540 its first drug brought to market without a larger pharmaceutical partner, the company changed that course last year. Chief Commercial Officer Liz Cermak has since said on numerous occasions that a larger company with a cardiovascular drug portfolio and global sales connections would be better positioned than tiny Pozen to commercialize the drug around the world.

The company aims for a global market for its cardiovascular drug, which will be affordably priced at about $1 per day. Cermak has said that the company is in talks with potential partners with the goal of securing a deal by the end of 2012.

PA32540 had been planned for a third quarter new drug application filing with the FDA. In discussing first quarter earnings, CEO John Platchetka acknowledged that the FDA’s questions might push back the filing. The FDA’s call for additional testing will likely delay that filing. It could also delay Pozen’s efforts to consumate a commercialization deal with a drug partner.