Drug developer

Adolor

(ADLR)

tanked Tuesday, falling nearly 50% after clinical trial results from the company and its Big Pharma partner

GlaxoSmithKline

(GSK) - Get Report

sent investors fleeing.

The companies were conducting studies designed to prove the safety and effectiveness of the drug Entereg, an experimental treatment for opioid-induced bowel dysfunction in patients with chronic noncancer pain.

While one of two identical phase III studies achieved its goal, the other did not. A phase IIb study of the drug also failed to reach its goal. However, both of the trials that missed their main targets did achieve a secondary objective of altering the average weekly frequency of spontaneous bowel movements, the companies said.

Adolor's shares were plunging $11.59, or 46%, to $13.38 on volume that was more than 40 times heavier than normal. By midday, nearly 18 million shares had traded, compared with the average total for a full session of just under 400,000.

The stock earlier traded as low as $11.85. Meanwhile, Glaxo was down 35 cents, or 0.6%, to $56.40.