** Shares of drug developer Unicycive Therapeutics UNCY.O fall 37.7% to $4.80 premarket

** UNCY says U.S. FDA declines to approve its drug, oxylanthanum carbonate, to treat elevated phosphate levels in patients on dialysis due to chronic kidney diseases

** Says health regulator's concerns not tied to the drug's efficacy or safety but to previously identified issues at a third-party manufacturing facility that the FDA hasn't inspected yet

** This is the second complete response letter the company has received; the first one was issued last year for the same third-party manufacturing deficiencies

** Co still in active talks with the FDA about labeling and plans to resubmit the application expeditiously

** As of last close, stock up 33.5% YTD