It was generally thought that opioids and skeletal muscle relaxants are useful therapy when combined with NSAIDs for acute low back pain but that's not the case. (Evgeny Atamanenko/Shutterstock)

People who went to the emergency department because of low back pain didn't get better pain relief from opioids or muscle relaxants than with a non-prescription painkiller, a randomized trial shows.

Low back pain is responsible for more than 2.5 million visits to U.S. emergency departments each year. Patients are usually treated with acetaminophen, skeletal muscle relaxants and a nonsteroidal anti-inflammatory drugs (NSAID) and opioids, often in combination.

Doctors in Bronx, New York, studied 323 patients who arrived at emergency with acute low back pain that started within the previous two weeks. 

All of the patients were asked to take 500 milligrams of the NSAID naproxen twice a day. A third of them were randomly assigned to also take the muscle relaxant cyclobenzaprine, a third to the opioid oxycodone and the rest to a placebo every eight hours as needed for lower back pain.

They all also received a standardized, 10-minute educational session before discharge.

Neither naproxen combined with oxycodone/acetaminophen nor naproxen combined with cyclobenzaprine offered better pain relief or better function after a week and after a month, lead author Dr. Benjamin W. Friedman of Montefiore Medical Center at Albert Einstein College and his co-authors reported in Tuesday's issue of JAMA.

The findings were surprising, Friedman said.

"I think it was generally believed that opioids and skeletal muscle relaxants are useful therapy when combined with NSAIDs for acute low back pain," Friedman said in an email to Reuters Health.

By three months after the emergency department visit, almost a quarter of the group said they still felt moderate to severe pain requiring medication, but less than three per cent said they had taken an opioid painkiller in the previous three days.

Low back injuries can occur from sprains caused by overstretching or tearing ligaments and strains or tears in tendon or muscle, according to the U.S. National Institute of Neurological Disorders and Stroke. 

"The classic mechanism of injury is lifting something too heavy," Friedman said. "But some patients just slept in an awkward position, some twisted the wrong way, some were in minor car accidents, some didn't stretch before going to the gym."

With files from Reuters