By Pat Anson, PNN Editor

Long-term use of muscle relaxants has nearly tripled in the U.S. since 2005, according to a new study by researchers at the University of Pennsylvania, who say the drugs are often prescribed inappropriately for chronic pain and to older adults.

Skeletal muscle relaxants (SMRs) like carisoprodol (Soma) and metaxalone (Skelaxin) were approved years ago for short-term treatment of muscle spasms and back pain. Researchers believe many doctors are now prescribing the drugs as an alternative to opioids for long-term pain management.

"There are few studies on the short-term efficacy and safety of skeletal muscle relaxants, and almost no data on their long-term effects, so it is very concerning that patients, and particularly older adults, are using these drugs for an extended period of time," said Charles Leonard, PharmD, an assistant professor of Epidemiology at Perelman School of Medicine. "Providers seem to be reaching for them despite incomplete information on their potential benefits and risks."

Medical guidelines generally recommend limiting the use of muscle relaxants to three weeks because they have not been shown to work for muscle spasms beyond that duration. The drugs can also have side effects such as falls, fractures, vehicle crashes, abuse and dependence. Because of those risks, muscle relaxants should be avoided altogether in elderly patients, according to the American Geriatrics Society.

To measure national trends in muscle relaxant prescribing, researchers analyzed the number of office visits that resulted in muscle relaxant prescriptions from 2015 to 2016. They found the number of new prescriptions remained stable at about 6 million per year. But office visits for renewals of muscle relaxant prescriptions tripled -- from 8.5 million in 2005 to 24.7 million in 2016.

Over two-thirds (67%) of the patients getting renewals for muscle relaxants in 2016 were also taking opioid medication, despite an FDA warning that co-prescribing the drugs could lead to respiratory depression and overdose. Older adults accounted for about one in four (22%) office visits for muscle relaxants.

"For older adults, I think the message should be to avoid using muscle relaxants, especially when we consider the side effects and increased risk of falls and fractures, and to find alternatives for pain management," said first author Samantha Soprano, MPH, a research coordinator and student in Penn's Master of Behavioral and Decision Sciences program.

In addition to potential side effects, researchers say muscle relaxants may not be any more effective in managing pain than medications like Tylenol or Advil.

"Muscle relaxants' place in therapy is really limited. Based on most guidelines, they're normally reserved as second- or third-line therapies," Leonard said. "Our findings suggest that prescribers may be reaching for these drugs sooner than that."

The findings are published in JAMA Network Open.