P005: ASSOCIATION BETWEEN METHOCARBAMOL USE AND PERIOPERATIVE RESPIRATORY OUTCOMES
Andrea A Lopez-Ruiz; Hiva Lee, MD; Steven Porter, MD; Ross Renew, MD
Mayo Clinic
Introduction/Background: Methocarbamol is a pharmacologic agent commonly used either synergistically with or as an alternative to opioids for pain management intraoperatively or in the outpatient setting. While the mechanism of action of methocarbamol in humans is not fully understood, it is hypothesized to act as a central nervous system (CNS) depressant. Given this, the Food and Drug Administration (FDA) suggests caution when combining methocarbamol with other CNS depressants such as alcohol or benzodiazepines. Although post-marketing surveillance data and case reports have identified instances of fatal interactions between methocarbamol and other CNS depressants, studies investigating the effects of methocarbamol on respiratory depression are lacking in the literature. The aim of this study was to investigate the effects of methocarbamol use on respiratory depression and perioperative outcomes.
Methods: A retrospective cohort study was conducted using data extracted from the electronic medical record at Mayo Clinic Florida. Inclusion criteria consisted of all surgical patients who received naloxone intraoperatively or in the post-anesthesia care unit (PACU) between 2018 and 2024. Data were loaded onto a secure REDCap database and manual chart review was performed to collect demographic information, intraoperative variables, and postoperative variables. Patients were stratified by methocarbamol exposure prior to naloxone administration: methocarbamol-exposed (n=20), which included outpatient, intraoperative, or PACU administration and methocarbamol-unexposed (n=219). The primary outcome reported was odds of requiring rapid response team activation. Secondary outcomes reported were odds of requiring supplemental oxygen or non-invasive ventilation. Data analysis was performed via GROK AI which utilized Python (pandas, scipy, statsmodels) with significance at p < 0.05. Multivariable logistic regressions models were used to assess the association between methocarbamol use and covariates including BMI, ASA status, surgery time, fentanyl dose, hydromorphone dose, and history of OSA and odds of requiring supplemental oxygen, non-invasive ventilation, or rapid response initiation.
Results: Non-opioid-naive patients were significantly more likely to have received methocarbamol prior to naloxone administration (65.0% vs 22.8%; p < 0.001). Furthermore, patients with an increased body mass index (BMI) were significantly more likely to require supplemental oxygen (aOR 1.09, 95% CI (1.01 - 1.18), p = 0.036) and/or non-invasive ventilation (NIV) (aOR 1.10, 95% CI (1.02 - 1.19), p = 0.015). Patients who received higher doses of hydromorphone were significantly more likely to require supplemental oxygen (aOR 3.80 95% CI (1.36 - 10.61), p = 0.011). Patients who received methocarbamol were more likely to require rapid response team activation compared to those who did not (aOR 20.12, 95% CI (0.59-686.70), p = 0.096), although this was not statistically significant.
Discussion/Conclusion: Overall, the data suggest that methocarbamol exposure is not associated with increased risk of respiratory depression or adverse perioperative outcomes. This study is limited by a small sample size, particularly in the methocarbamol-exposed group, which limits statistical power and highlights the need for further research to investigate potential adverse effects of methocarbamol with respect to respiratory depression.