What muscle relaxants are recommended for treating back pain?

Muscle Relaxants for Back Pain

Direct Recommendation

Tizanidine is the preferred muscle relaxant for back pain, with the strongest evidence supporting its efficacy and safety profile, particularly when combined with NSAIDs or acetaminophen. 1, 2

Treatment Algorithm

Step 1: First-Line Therapy

• Begin with NSAIDs as first-line pharmacological treatment before considering muscle relaxants 2
• Acetaminophen is a reasonable alternative with better safety profile, though slightly less effective 2

Step 2: Adding a Muscle Relaxant

• Add tizanidine if pain is inadequately controlled with NSAIDs/acetaminophen alone, or if muscle spasm is a prominent feature 2
• Start tizanidine at 2-4 mg, titrating upward as needed 1, 2
• In older adults or those at higher risk for adverse effects, begin with 2 mg up to three times daily 1

Step 3: Special Considerations for Radiculopathy

• For back pain with leg symptoms (radiculopathy), combine tizanidine with gabapentin as adjunctive therapy 1, 2
• Gabapentin demonstrates small, short-term benefits specifically in radiculopathy patients 1, 2

Evidence Supporting Tizanidine Over Other Options

Why Tizanidine is Superior

• Tizanidine demonstrated efficacy in 8 high-quality trials for acute low back pain, the most robust evidence base among muscle relaxants 1
• When combined with acetaminophen or NSAIDs, tizanidine consistently provides greater short-term pain relief than monotherapy 1
• Combination therapy may reduce gastrointestinal adverse events (RR 0.54) when used with NSAIDs 1

Cyclobenzaprine: The Alternative with Weaker Evidence

While cyclobenzaprine is commonly prescribed, the evidence is less compelling:

• Only 1 lower-quality trial exists for chronic low back pain, which did not report pain intensity or global efficacy 1
• Meta-analysis shows cyclobenzaprine is nearly 5 times more likely than placebo to produce symptom improvement by day 14 (OR 4.7), but the effect is modest (effect size 0.38-0.58) 3
• The FDA label indicates cyclobenzaprine's efficacy was demonstrated in trials, but combination with naproxen was associated with more side effects, primarily drowsiness 4, 5
• The effect is greatest in the first 4 days of treatment, declining after the first week 3

Other Muscle Relaxants: Limited Evidence

• Baclofen has sparse evidence (only 2 trials) for low back pain despite efficacy in spasticity 1
• Methocarbamol does not directly relax skeletal muscles and has no evidence of efficacy in chronic pain 1
• Carisoprodol's usefulness is limited by abuse potential 6

Safety Profile and Monitoring

Common Adverse Effects

• All skeletal muscle relaxants increase CNS adverse events (RR 2.04) compared to placebo, with drowsiness being most common 1, 7
• Total adverse events increase with muscle relaxants (RR 1.50) 1
• Combination therapy with tizanidine increases CNS adverse events (RR 2.44) 1

Specific Monitoring for Tizanidine

• Monitor for hypotension and sedation, the most common dose-related adverse effects 1
• Monitor for hepatotoxicity, which is generally reversible 1, 2
• Serious complications are rare, and most adverse events are self-limited 1

Treatment Duration: Critical Pitfall to Avoid

Limit muscle relaxant use to short-term courses (7-14 days maximum) to reflect the evidence base from clinical trials 1, 2

• Time-limited courses are recommended due to limited evidence on long-term benefits and risks 1, 2
• Assessment of response should occur within 2-4 days for acute pain relief 1
• Reassess diagnosis and consider alternative therapies if no improvement after a time-limited course 1, 2
• The efficacy of cyclobenzaprine declines after the first week, suggesting shorter courses may be better 3

Key Clinical Pearls

• The concept of "muscle relaxant" is somewhat a misnomer—these drugs likely work through sedative properties rather than directly relaxing skeletal muscle 1
• Tizanidine's efficacy is independent of sedation, though sedation remains a common side effect 1
• Combining muscle relaxants with NSAIDs provides consistently greater pain relief than monotherapy in high-quality trials 1
• Number needed to treat for cyclobenzaprine is 2.7 (meaning fewer than 3 patients need treatment for 1 to improve) 3