Safety of Intravenous Methocarbamol in Patients With Renal Impairment

Introduction: Methocarbamol is a skeletal muscle relaxant commonly used in multimodal analgesia and has been shown to reduce postoperative opioid use. Due to the presence of polyethylene glycol, its intravenous (IV) formulation is contraindicated in patients with renal impairment per prescribing information. However, clinical evidence supporting this caution is limited. This study aimed to evaluate safety of the short-term use of IV methocarbamol in hospitalized patients with impaired renal function.


Methods: We conducted a multicenter, retrospective cohort study comparing patients with baseline renal impairment (study group) to those with normal renal function (control group). Adults hospitalized for 48 hours or longer who received at least 3 doses of IV methocarbamol were included. Exclusion criteria included dialysis at admission, uncontrolled sepsis, diabetic ketoacidosis, or drug overdose. Primary outcomes were a composite of mortality, new renal replacement therapy, and persistent renal dysfunction, as well as the incidence of acute kidney injury (AKI). Secondary outcomes included in-hospital mortality, length of stay, and metabolic acidosis. Safety outcomes included central nervous system (CNS) effects, hypotension, bradycardia, and drug discontinuation.


Results: Of 250 patients, 96 were in the study group and 154 in the control group. The study group was older (75.2 vs. 53.9 years, p < 0.001), had lower creatinine clearance (47.6 vs. 89.2 mL/min, p < 0.001), and more chronic kidney disease (33.3 percent vs. 1.3 percent, p < 0.001). The control group received higher cumulative methocarbamol doses (5000 vs. 3875 mg, p < 0.001) and opioids (167.5 vs. 126.3 morphine equivalents, p = 0.011). The incidence of AKI was similar (6.3 percent vs. 3.9 percent, p = 0.397); no patients required new dialysis or had persistent renal dysfunction. Acid-base parameters and metabolic acidosis rates did not differ significantly. CNS effects, hypotension, bradycardia, and adverse events leading to discontinuation were rare and comparable.


Conclusions: IV methocarbamol was well tolerated in patients with renal impairment and was not associated with increased renal or systemic toxicity. These findings support its short-term safety in this population when used appropriately.