UPDATE 1-CombinatoRx: Neuromed pain drug may not get approval

* Neuromed to determine appropriate actions

* CombinatoRx shares fall 34 pct in premarket trade

Nov 16 (Reuters) - CombinatoRx Inc CRXX.O, which is merging with privately held Neuromed Pharmaceuticals Inc, said U.S. health regulators have indicated to Neuromed that its experimental pain drug, Exalgo, may not be approved.

Neuromed is seeking regulatory approval of the opioid drug for patients who no longer get relief with other similar medications.

Based on discussions with the U.S. Food and Drug Administration staff, Neuromed is trying to determine the appropriate actions that may include amending the existing drug application, or resubmitting it under a separate section, which utilizes different criteria to determine the basis for approval.

The U.S. rights to Exalgo were acquired by Mallinckrodt Inc, a Covidien Plc COV.N unit, on June 11.

CombinatoRx and Neuromed agreed to merge on June 30. The deal is expected to close in the fourth quarter.

Shares of CombinatoRx were down 34 percent to $1.08 in premarket trade. They closed at $1.63 Friday on Nasdaq. (Reporting by Esha Dey in Bangalore; Editing by Aradhana Aravindan)