(Reuters) - Repros Therapeutics Inc said the U.S. health regulator sought additional studies of its testosterone replacement drug, Androxal, and recommended that a safety study of the drug be extended, delaying potential approval.
Shares of the company fell 33 percent in premarket trading.
Repros said the company's marketing approval application would be delayed to the fourth quarter of 2014, if the results of the study have to be included.
The company was earlier expecting to file the application in mid-2014.
Analysts said the slight delay could be a positive.
"We see Androxal's profile as approvable and the added time to improve the dataset is worthwhile, considering some flaws in conduct of the first Phase III studies," Lazard Capital analyst Joshua Schimmer wrote in a note to clients.
The U.S. Food and Drug Administration suggested Repros exclude one site where the late-stage study of the drug was conducted due to data fraud.
The company said the drug met both the main goals of improving sperm count and testosterone levels in the late-stage study even without data from that site.
The regulator said it would consider different goals related to sperm count than those previously agreed upon with the company, and new studies have to be conducted.
The FDA agreed to studies comparing Androxal with approved testosterone replacement drugs, the results of which could be included in the label if Androxal showed superiority to those drugs, Repros said.
The company is designing two studies that could be completed and submitted to the FDA in the fourth quarter next year.
Brean Capital analyst Jonathan Aschoff said the drug's adoption rate, if it is approved, could increase if the label showed it was superior to existing testosterone drugs.
Repros stock was down at $15.80 in premarket trading on Wednesday.
(Reporting by Vrinda Manocha in Bangalore; Editing by Kirti Pandey)