U.S. Markets closed

1-AcelRx's opioid painkiller succeeds in key study

(Adds study details, stock movement)

Sept 15 (Reuters) - AcelRx Pharmaceuticals Inc said its experimental opioid painkiller was well tolerated in post-operative patients, including those with organ impairment and the elderly, in a late-stage study.

The Redwood City, California-based drugmaker's stock was up about 23 percent at $4.04 in premarket trading.

The trial was designed to assess the drug's safety in patients who do not require long-term pain relief following surgery.

Nearly two in three patients had no adverse events during the 140-patient study, and the most common adverse events were nausea and headache, the company said on Thursday.

AcelRx said it intends to submit an application to market the drug to the U.S. Food and Drug Administration by the end of 2016.

The company is also developing the therapy to manage moderate-to-severe acute pain in a variety of other medically supervised settings, including emergency medicine, outpatient or ambulatory surgery, non-surgical patients experiencing pain in the hospital.

The abuse of opioids - a class of drugs that include heroin and prescription painkillers - has long been a concern. An overdose can produce euphoric highs and even disrupt parts of the brain that control breathing.

(Reporting by Akankshita Mukhopadhyay in Bengaluru; Editing by Maju Samuel)