Pozen’s stock fell 18 percent on Thursday after the Chapel Hill company announced that federal regulators may delay approval of its experimental cardiovascular drug PA32540.

The company said Wednesday that federal regulators have preliminarily decided the drug did not meet an approval milestone and have recommended further study. Pozen is seeking approval to market the drug as a replacement for aspirin in the prevention of heart disease and stroke in patients at high risk for developing ulcers from aspirin use.

PA32540, which is now in the final stages of clinical trials, is an experimental combination of aspirin and a modified version of omeprazole (Prilosec).

The FDA also told Pozen that PA32540 approval will also probably require an in vivo study of the bioequivalence of the lower-dose version of the drug, which could add money and time to the approval process.

Staff writer Gloria Lloyd