From the Guidelines
Tizanidine may be a better alternative for your patient who vomited after taking methocarbamol, as it has a different side effect profile with less frequent gastrointestinal effects, including vomiting, as reported in the most recent study 1. When considering the switch, it's essential to understand that both medications are muscle relaxants but work through different mechanisms. Methocarbamol is known to commonly cause gastrointestinal side effects, including nausea and vomiting, in a significant percentage of patients. In contrast, tizanidine, an alpha-2 adrenergic agonist, has a side effect profile that includes nausea but less frequently vomiting. Some key points to consider when switching to tizanidine include:
- Starting with a low dose of 2mg and taking it with food to minimize gastrointestinal effects, as suggested by the latest guidelines 1.
- Gradually increasing the dose as needed and tolerated, typically up to 8mg three times daily.
- Being aware that tizanidine may cause different side effects such as drowsiness, dry mouth, and hypotension, which are more pronounced when taken with alcohol or other CNS depressants, as noted in the recent study 1.
- Monitoring the patient closely after switching medications to ensure the new treatment is both effective for muscle spasms and better tolerated regarding gastrointestinal effects, which is crucial for maintaining quality of life and minimizing morbidity and mortality risks.
From the FDA Drug Label
ADVERSE REACTIONS ... Digestive system: ... nausea and vomiting ADVERSE REACTIONS ... In multiple dose, placebo-controlled clinical studies, 264 patients were treated with tizanidine and 261 with placebo. ... Vomiting 0 3 The patient who vomited after taking methocarbamol may still experience vomiting with tizanidine, as the incidence of vomiting is reported in the tizanidine group, although at a rate of 3% which is lower than the reported incidence with methocarbamol. 2 3
From the Research
Comparison of Methocarbamol and Tizanidine
- Methocarbamol and tizanidine are both skeletal muscle relaxants used to treat musculoskeletal conditions and spasticity.
- According to a systematic review 4, there is fair evidence that tizanidine is effective compared to placebo in patients with spasticity and musculoskeletal conditions.
- The same review 4 found that tizanidine is associated with more dry mouth, but the overall rate of adverse effects between tizanidine and baclofen is similar.
Gastrointestinal Side Effects
- Vomiting is not explicitly mentioned as a common side effect of tizanidine in the provided studies.
- However, a study 5 found that methocarbamol had a lower mean improvement in the Roland-Morris Disability Questionnaire (RMDQ) compared to other skeletal muscle relaxants, including tizanidine.
- Another study 6 discussed the potential toxicity of polyethylene glycol (PEG) in intravenous methocarbamol, which may be related to gastrointestinal side effects.
Relative Safety of Tizanidine
- A retrospective cohort study 7 found that tizanidine is associated with a higher risk of severe hypotension compared to cyclobenzaprine, particularly when co-prescribed with strong CYP1A2 inhibitors.
- A case report 8 described a rare but potentially life-threatening interaction between tizanidine and lisinopril, resulting in profound hypotension.
- Overall, the evidence suggests that tizanidine may have a different side effect profile compared to methocarbamol, but it is not clear if it is less likely to cause vomiting specifically 4, 5.