Safety of Baclofen and Tizanidine in Older Adults: A Retrospective Cohort Study in a Large Integrated Health Care System.

The AGS 2023 updated Beers Criteria for potentially inappropriate medication use in older adults recommends avoidance of skeletal muscle relaxants (SMRs) for musculoskeletal complaints. Two SMRs, baclofen and tizanidine, are excluded from this criterion. Clinicians may therefore consider baclofen or tizanidine as options for older adult patients with musculoskeletal complaints; however, evidence for this conclusion is lacking. To investigate injury events associated with baclofen and tizanidine in older adults compared to cyclobenzaprine, an SMR included in the Beers Criteria. We conducted a retrospective cohort study at Kaiser Permanente Southern California (KPSC) in patients age 65 to 99 years. Participants were identified as KPSC members dispensed a study SMR between January 1, 2008, and December 31, 2018. Serious injury events were identified in the electronic medical record using ICD-9 and ICD-10 codes for the following: fracture, fall leading to fracture, brain injury, and dislocation injury. Findings were adjusted for numerous demographic and clinical covariates. Secondary analyses investigated injury-free probabilities based on the type of injury event. From a population of 87,896 participants, 118,426 study medication episodes were identified. Compared with cyclobenzaprine, baclofen demonstrated a 69% greater risk (adjusted Hazard Ratio [aHR] 1.69, 95% Confidence Interval [CI] 1.51-1.88), and tizanidine carried a 34% greater risk (aHR 1.34, 95% CI 1.11-1.62) for composite injury outcomes. Both baclofen and tizanidine demonstrated lower injury-free probabilities over time when compared with cyclobenzaprine. Older adult patients dispensed baclofen or tizanidine were found to have an increased risk of injury when compared with cyclobenzaprine, currently included on the Beers Criteria. These findings support the inclusion of baclofen and tizanidine on the Beers Criteria along with other SMRs as potentially inappropriate medications in use in older adults with musculoskeletal complaints. Due to a retrospective design, the risk for residual confounding may remain.