Drug developers Adolor Corp. and GlaxoSmithKline PLC said early Monday the Food and Drug Administration has requested more safety data on their postoperative bowel treatment Entereg.

The agency sent the companies an approvable letter on the drug, requesting 12-month safety data that includes analysis of serious cardiovascular events from an ongoing study and a risk management plan. The ongoing study is expected to be complete by the first quarter of 2007, with data available during the second quarter.

Adolor shares plummeted $4.24, or 30.4 percent, to $9.70 in premarket trading on the INET electronic exchange, indicating that stock may open at a new 52-week low. Shares, which closed Friday at $13.94 on the Nasdaq, have ranged between $11.28 and $27.80 over the past year.

Shares of British firm GlaxoSmithKline shed 16 cents to reach $53.14, having closed at $53.30 Friday on the NYSE.

Part of the application for approval, submitted in September, included data showing an increase in the reported incidence of serious cardiovascular events, though the company said they were not statistically significant. Patients experiencing the heart trouble were already at high risk for cardiovascular disease, Adolor said, and the results were consistent with epidemiological expectations.

Postoperative ileus occurs in almost all patients after abdominal surgery. Coordinated movements in the gastrointestinal tract are disrupted, causing nausea, vomiting, abdominal swelling and bloating.

"We will meet with the FDA to discuss the approvable letter and work with GlaxoSmithKline to provide the additional information requested as expeditiously as possible," said David Madden, Adolor's interim president and chief executive, in a statement.

Entereg is also being studied as a possible treatment to relieve constipation in people who must take opiates for cancer and other chronic pain. Phase III clinical trials for that purpose showed mixed results in the drug's effectiveness.