MODERATE RECOMMENDATION One high quality article (Skrejborg 2020) evaluated the use of an oral relaxant (Chlorzoxazone) compared to placebo, administered for the first 7 days after TKA or THA. No significant differences were found in pain after a 5-minute walk on POD 1 or pain at rest during the first 24 hours after surgery. No significant differences were found in Oxford Hip Score or Oxford Knee Score at 7 days or 12 months after surgery. There were also no significant differences found in opioid consumption during the first 7 days after surgery or for side effects, such as fatigue, dizziness, nausea, or vomiting while hospitalized after surgery.
Benefits/Harms of Implementation
While there are multiple potential side effects of relaxants, such as drowsiness, dizziness, lightheadedness, headaches, and gastrointestinal upset, none were identified in this study. These should be evaluated in any future research in this area. In addition, this study did not assess for differences based on patient sex or gender, so differences in potential harms among sexes is not known.
Cost Effectiveness/Resource Utilization
While approved in the US and available for relatively low cost, the lack of efficacy noted in this study does not support the use of Chlorzoxazone for this indication, and the additional cost is not offset by lower use of opioids.
Acceptability
Chlorzoxazone is also approved for use in the US but based on one-high quality study, does not seem to improve post-operative pain or function or lower opioid use.
Feasibility
Chlorzoxazone appears to be a readily available medication in the US, but additional research is needed to determine if this, or other oral relaxants, given during the perioperative period have significant benefit in terms of pain, opioid use, or function, before recommending their routine use.
Future Research
With the need to decrease opioid prescribing and the trend of shorter hospital stays, use of non-opioid oral medications after TKA and THA to improve patient function with lower risks of side effects needs additional investigation. This could include the use of oral muscle relaxants. Given the differences in nociception and pharmacokinetics and pharmacodynamics among the sexes, future research on the use of relaxants in this setting should include assessments of outcomes based on patient sex.