UF study finds some combinations of opioids and muscle relaxants are safe, others raise overdose risk

Researchers in the University of Florida College of Pharmacy have identified certain combinations of muscle relaxants and opioid prescriptions that are safe, while others increase the risk of opioid overdoses and should be avoided.

Two bottles of prescription pills.The findings are published in July’s issue of Clinical Pharmacology & Therapeutics, the flagship journal of the American Society of Clinical Pharmacology & Therapeutics.

Skeletal muscle relaxants, or SMRs, are commonly prescribed medications used to relieve muscle spasms associated with painful conditions, such as lower back pain. They hold promise in combatting the opioid crisis because they can reduce the need for high opioid doses in treating pain.

However, previous studies have shown that SMRs were used by patients who experienced opioid overdoses, which raises the question of whether SMRs are contributing to the problem, rather than alleviating it. The Centers for Disease Control and Prevention, or CDC, cautions against the co-prescribing of muscle relaxants and opioids over concerns about combined effects on reduced brain function. The UF study provides the first epidemiological evidence to support and further enhance the CDC’s recommendation.

After evaluating the medical records of more than 19 million patients from a large insurance database, UF researchers found that short-term use of SMRs and opioids poses no greater risk than using opioids alone. However, using SMRs and opioids in combination for several weeks, or combining SMRs with high-dose opioids, increased the risk of overdosing.

Across different SMRs, combining baclofen or carisoprodol with opioids was particularly problematic, while cyclobenzaprine seemed to be a safe option. Additionally, the study’s authors found the triple combination of opioids, SMRs and tranquilizing medications known as benzodiazepines is unsafe.

The study’s results could have a major impact on prescribing decisions and patient outcomes, as previous studies have shown an estimated 10% to 30% of opioid users also use a muscle relaxant.

“In clinical practice, most patients only use opioids and muscle relaxants for short-term pain relief, and our study provides assurance on the safety of this practice,” said Almut Winterstein, Ph.D., R.Ph., a professor and the Dr. Robert and Barbara Crisafi Chair for Pharmaceutical Outcomes and Policy in the UF College of Pharmacy, part of UF Health, and director of the Center for Drug Evaluation and Safety. “This is an important message as clinicians are looking for options to provide adequate pain management while reducing opioid use.”

UF researchers hope the findings can enhance the care of millions of patients who are suffering from musculoskeletal pain issues.

Yan Li, Ph.D., a 2019 graduate of the UF College of Pharmacy, served as the lead author of the study. His collaborators included Winterstein and multiple researchers from the University of Florida and the University of Kentucky College of Pharmacy.

The study was first published digitally in February 2020.