What is the recommended muscle relaxant (e.g. cyclobenzaprine, methocarbamol) for acute back pain?

Muscle Relaxant for Back Pain

Direct Recommendation

Tizanidine is the preferred muscle relaxant for acute back pain, with the strongest evidence supporting its efficacy and a favorable safety profile compared to other options like cyclobenzaprine or methocarbamol. 1

Treatment Algorithm

First-Line Approach

• Start with NSAIDs or acetaminophen alone before adding a muscle relaxant, as these provide effective pain relief for most patients with acute back pain 2
• NSAIDs are slightly more effective than acetaminophen for pain relief 1

When to Add a Muscle Relaxant

• Add a muscle relaxant if pain is not adequately controlled with NSAIDs/acetaminophen alone, or if muscle spasm is a prominent clinical feature 2
• Tizanidine is the recommended choice, demonstrated effective in 8 clinical trials for acute low back pain 1

Tizanidine Dosing

• Start with 2-4 mg up to three times daily 1
• Begin with 2 mg three times daily in older adults or those at higher risk for adverse effects 1
• Titrate upward as needed based on response 1

Combination Therapy

• Adding tizanidine to acetaminophen or an NSAID provides consistently greater short-term pain relief than monotherapy in high-quality trials 1
• This combination approach may reduce gastrointestinal adverse events (RR 0.54) when combined with NSAIDs 1

Why Not Cyclobenzaprine or Methocarbamol?

Cyclobenzaprine Limitations

• Limited evidence base: Only 1 lower-quality trial for chronic low back pain that did not report pain intensity or global efficacy 1
• FDA-approved only for short-term use (2-3 weeks) as adjunct to rest and physical therapy 3
• While older studies showed some efficacy at 5-10 mg three times daily 4, the evidence quality is inferior to tizanidine 1
• Recent research shows no added benefit: A 2018 randomized trial found that naproxen plus methocarbamol provided no functional improvement over naproxen plus placebo 5
• Another study demonstrated that cyclobenzaprine 5 mg three times daily combined with ibuprofen was not superior to cyclobenzaprine alone 6

Methocarbamol Limitations

• Does not directly relax skeletal muscles according to FDA labeling 7
• No evidence of efficacy in chronic pain 8
• The 2018 ED trial showed methocarbamol added to naproxen did not improve Roland-Morris Disability Questionnaire scores compared to naproxen alone (improvement 8.1 points vs 10.9 points with placebo) 5
• Not favored for chronic pain in older adults due to potential adverse effects 8

Special Consideration for Radicular Pain

If back pain includes leg symptoms (radiculopathy):

• Tizanidine remains the preferred muscle relaxant 1, 2
• Consider adding gabapentin, which has demonstrated small, short-term benefits specifically in patients with radiculopathy 1, 2
• Combining tizanidine with gabapentin may be beneficial for radicular symptoms 1

Critical Safety Considerations

All Muscle Relaxants

• All skeletal muscle relaxants increase CNS adverse events (RR 2.04) compared to placebo, with sedation being the most common 1
• Total adverse events increase by 50% (RR 1.50) compared to placebo 1
• Limit treatment duration to 1-2 weeks due to limited evidence on long-term benefits and risks 2

Tizanidine-Specific Monitoring

• Monitor for sedation and hypotension, the most common dose-related adverse effects 1
• Monitor for hepatotoxicity, which is generally reversible 1, 2
• Reassess after 2-4 days for acute pain relief 1

Common Pitfalls to Avoid

• Do not use muscle relaxants as first-line monotherapy - always start with NSAIDs or acetaminophen 2
• Avoid prolonged courses - reassess diagnosis and consider alternative therapies if no improvement after a time-limited course 1
• Do not prescribe cyclobenzaprine or methocarbamol based on historical practice patterns - the evidence does not support their superiority over placebo when combined with NSAIDs 5
• Recognize that "muscle relaxant" is a misnomer - these drugs do not directly relax skeletal muscle and likely work through sedative properties 8, 7