Metaxalone Should Be Held on the Day of Surgery
Metaxalone must be discontinued on the morning of the surgical procedure prior to induction of general anesthesia 1. This is a clear, consensus-based recommendation from the Society for Perioperative Assessment and Quality Improvement (SPAQI) 2021 guidelines.
Rationale for Discontinuation
Metaxalone is a centrally acting skeletal muscle relaxant with an unclear mechanism of action that does not directly affect skeletal muscle 1, 2. The primary concerns for perioperative management include:
- CNS depression effects: Drowsiness, dizziness, and sedation that are additive with anesthetic agents 2
- Enhanced CNS depression when taken with food, making elderly patients especially susceptible 2
- Potential for impaired mental and physical abilities that compound with other CNS depressants including alcohol, benzodiazepines, opioids, and anesthetic agents 2
Timing of Discontinuation
Hold metaxalone on the day of operation - meaning the morning dose should be withheld 1. The pharmacokinetics support this approach:
- Peak plasma concentrations occur approximately 3 hours after oral administration under fasted conditions 2
- Terminal half-life is 9.0 ± 4.8 hours under fasted conditions 2
- The drug is extensively distributed in tissues (apparent volume of distribution ~800 L) due to its lipophilicity 2
Important Clinical Considerations
No tapering is required for metaxalone discontinuation, unlike some other centrally acting muscle relaxants (e.g., carisoprodol requires 4-9 day taper, cyclobenzaprine benefits from 2-3 week taper) 1. Metaxalone does not carry the same withdrawal risk profile.
Contraindications to be aware of:
- Significant hepatic dysfunction (metaxalone is metabolized by the liver via multiple CYP enzymes) 1, 2
- Significant renal dysfunction 1
- History of drug-induced, hemolytic, or other anemias 1
Anesthetic Implications:
The sedative effects are additive with all CNS depressants used in anesthesia 2. This includes:
- Benzodiazepines
- Opioids
- Propofol and other induction agents
- Volatile anesthetics
Common Pitfall
Do not confuse metaxalone with neuromuscular blocking agents used during anesthesia. Metaxalone does not act on the neuromuscular junction or contractile mechanism of striated muscle 2. The concern is purely related to central nervous system depression and potential drug interactions with anesthetic agents, not interference with controlled neuromuscular blockade.
If a patient inadvertently takes metaxalone on the morning of surgery, the anesthesiologist should be informed to anticipate potentially enhanced CNS depression and adjust anesthetic dosing accordingly, particularly in elderly patients who are more susceptible to these effects 2.