A commonly prescribed muscle relaxant known as baclofen can leave older kidney patients so disoriented they land in the hospital, a new study warns.

"It can present with acute stroke-like symptoms, even though it's not a stroke," said senior researcher Dr. Amit Garg, a professor of nephrology at Western University in Ontario, Canada. "It can present with dementia-like symptoms."

About 1 in 25 people with low kidney function prescribed high doses of baclofen wound up being admitted to a hospital for severe confusion, according to a study of nearly 16,000 older Canadians with chronic kidney disease.

By comparison, only one in 500 kidney patients not prescribed baclofen wound up hospitalized for confusion.

"There was a pretty marked difference in risk," Garg said, noting these findings "highlight a potential risk associated with these drugs that hasn't been fully appreciated."

Other seniors might also face this risk, since kidney function often declines as people grow older, he added.

Baclofen is typically prescribed to people suffering muscle spasms, Garg said. Doctors hand out more than 8 million prescriptions of baclofen every year. It's sold under a number of different brand names, including Lioresal, Gablofen and Kemstro.

The drug leaves the body when the kidneys filter it out of a person's blood, Garg explained.

"If someone's kidney function isn't working very well, that means the drug is accumulating in the system," he said.

Garg and other doctors had started noticing kidney patients on baclofen sometimes became disoriented and dazed.

For example, nephrologist Dr. Holly Koncicki remembers some dialysis patients showing up with noticeably clouded mental capacity.

"Of those I can remember, they often presented with confusion or being very sleepy and lethargic," said Koncicki, of the Icahn School of Medicine at Mount Sinai, in New York City.

In the Canadian study, Garg and his colleagues combed the medical literature and found 30 prior case reports linking baclofen to hitches in brain function, so they decided to more closely study this potential problem.

The researchers pulled health data on nearly 16,000 older Ontario residents with chronic kidney disease who had been prescribed baclofen between 2007 and 2018.

The investigators compared those patients' hospitalizations for mental conditions against those from a group of almost 300,000 kidney patients who had not been prescribed the drug.

Patients were at greatest risk of hospitalization for confusion if their kidney function was very impaired – 30% or less – and they had been prescribed a high dose of baclofen, more than 20 milligrams (mg) per day.

But even patients with kidney function as high as 60% had an increased risk of confusion when prescribed high doses of baclofen, the findings showed. About 1 in 5 older adults live with kidney function of less than 60%.

Kidney patients prescribed baclofen at 20 mg/day or higher had nearly 20 times the relative risk of being hospitalized for an altered mental state, compared with patients not taking the drug, the researchers found.

Doses lower than 20 mg/day were associated with a nearly sixfold increase in kidney patients' risk of hospitalization.

The results were published online Nov. 9 in the Journal of the American Medical Association, to coincide with a planned presentation at the American Society of Nephrology annual meeting, in Washington, D.C.

Koncicki, who was not involved with the study, said, "In our older patients with impaired kidney function, there should be cautious use of this medication."

Garg added that the effect might be even more widespread than what was found in the study, which only considered people so severely affected that they landed in the hospital.

He said he's concerned that many more people "might have more subtle changes in their thinking who we aren't even picking up in this study."

People already taking baclofen should keep taking the drug but ask their doctor about these possible mental side effects, Koncicki and Garg said.

Patients "should feel empowered to ask questions about the risks and benefits of medications," Koncicki said, "and side effects to watch out for so they can make an informed decision about whether a medication is right for them."

Dr. Teresa Murray Amato, director of geriatric emergency medicine at Northwell Health in New Hyde Park, N.Y., agreed.

"All patients should speak to their doctors regarding side effects of all medications," Murray Amato said. "For patients over 65, make sure you understand your kidney function and ask about potential renal dosing on all medications. If you are on baclofen now, make sure you contact your health care provider so that you can have an expedited conversation."

"Please seek emergency care if you or your family member is showing any signs of altered [mental activity] and you suspect medications may be involved," Murray Amato said.

Regulatory agencies also might consider strengthening the drug warning for baclofen to include this potential effect, Garg said.