UPDATE 1-Repros to stop using 50 mg dose in fibroids study

* To stop using higher dose due to rise in liver enzymes

* To discuss late-stage study endpoints with FDA in Sept

* Shares fall about 5 pct in trading before the bell

July 1 (Reuters) - Repros Therapeutics Inc (RPRX.O) said it would discontinue the use of the higher, 50 mg dose in its ongoing studies to treat uterine fibroids and associated anemia, after a few patients discontinued the treatment due to adverse events.

Shares of the company were trading down about 5 percent at $6.86 before the bell. They closed at $7.19 Tuesday on Nasdaq.

Repros said it would discontinue the use of the higher dosage after it found dose-dependent increase in liver enzymes -- a marker for toxicity -- in a low percentage of women.

Repros, which focuses on drugs to treat reproductive system disorders, is developing its lead drug, Proellex, to treat symptoms associated with uterine fibroids and endometriosis.

Endometriosis is a condition where tissue similar to the lining of the uterus are found elsewhere in the body and symptoms include pelvic pain, infertility and severe fatigue.

The company, which completed a mid-stage study of the drug earlier this year, said Proellex showed no efficacy differences between the 25 mg and 50 mg doses in the study.

Repros plans to initiate the late-stage studies with the 12.5 mg and 25 mg doses for endometriosis in the fourth quarter of this year and the first quarter 2010, in both the United States and in Europe.

Repros will also begin additional studies with the 12.5 mg dose to supplement the overall efficacy and safety profile of the drug, and does not expect the studies to delay the timing of its regulatory submissions.

For the alerts double-click [ID:nWNAB3576] . (Reporting by Anand Basu in Bangalore; Editing by Deepak Kannan)