Amrutha Penumudi : Repros Therapeutics Inc will abandon efforts to seek approval for its testosterone drug in the United States if an ongoing study fails, and shift focus to its uterine fibroids drug that showed promise in a mid-stage trial.

Repros said on Tuesday its uterine fibroids drug Proellex stopped severe menstrual bleeding in 52 percent of women enrolled in the trial, pushing the company's shares up 175 percent the next day.

The shares continued their climb on Thursday, hitting their highest in five and a half months.

The results offered some hope to the tiny drug developer, whose testosterone drug Androxal was rejected by the U.S. Food and Drug Administration in December, sending its shares into a spiral over the next few months.

Repros is conducting an additional study in response to the FDA's request for more data on Androxal, a drug that aims to treat secondary hypogonadism, a condition that leads to low testosterone levels in men, in combination with diet and exercise.

"We'll know before the beginning of June whether there's a benefit; if not I'm not going to pursue it and we're going to focus all our efforts on Proellex," Chief Executive Joseph Podolski told Reuters.

"That said, I am willing to bet that Androxal is going to show results," he said.

Repros applied for U.S. marketing approval for Androxal in February 2015, based on data from four studies, two of which compared the drug to a leading FDA-approved treatment.

The FDA rejected the application, saying the design of the studies was not adequate to demonstrate clinical benefit.

The health regulator tightened its rules on the use of testosterone drugs last year, saying they should be reserved for patients with specific conditions, such as genetic disorders or tumors that impair the function of the testicles.

There is still hope for Androxal in Europe, where regulators had a more positive outlook on it.

With Androxal's future in doubt, the focus has shifted to Proellex, which has shown encouraging results in uterine fibroids and endometriosis, a disease in which tissue that normally grows inside the uterus grows outside it.

The standards of care for uterine fibroids and endometriosis consist of surgery or short-term treatment with hormonal drugs, which cause loss in bone density. They are not recommended for use for more than six months.

Laidlaw & Co analyst Yale Jen said the potential sales for the two indications combined could exceed $1 billion. (Reporting by Amrutha Penumudi in Bengaluru; Editing by Sayantani Ghosh and Don Sebastian)