What muscle relaxants are recommended for treating back pain?

Muscle Relaxants for Back Pain

Primary Recommendation

For acute low back pain, skeletal muscle relaxants are moderately effective for short-term pain relief (2-4 days), with tizanidine being the preferred agent, though cyclobenzaprine has the most robust clinical trial evidence. 1, 2

Treatment Algorithm

First-Line Approach

• Start with NSAIDs or acetaminophen before adding a muscle relaxant, as recommended by the American College of Physicians 1
• NSAIDs are slightly more effective than acetaminophen for pain relief 3
• Add a muscle relaxant only if pain is inadequately controlled or if muscle spasm is a prominent clinical feature 1

Muscle Relaxant Selection

For Acute Low Back Pain:

• Tizanidine is the preferred muscle relaxant based on American College of Physicians recommendations, starting at 2-4 mg and titrating as needed 1, 2
• Tizanidine demonstrated efficacy in 8 trials for acute low back pain 3
• Cyclobenzaprine is a well-supported alternative with the most extensive clinical trial data (1,405 patients in recent trials) 4
• Cyclobenzaprine 5 mg three times daily is effective, with statistically significant superiority over placebo by day 3-4 and day 8 4
• Patients on cyclobenzaprine are nearly 5 times more likely to report symptom improvement by day 14 (odds ratio 4.7; 95% CI 2.7-8.1) 5

For Low Back Pain with Radiculopathy (Leg Pain):

• Tizanidine remains the preferred muscle relaxant for radicular symptoms 2
• Add gabapentin as adjunctive therapy for radiculopathy, which provides small, short-term benefits specifically for nerve root involvement 1, 2
• Avoid systemic corticosteroids—they are ineffective for sciatica 2

Agents with Limited Evidence:

• Baclofen and dantrolene have sparse evidence (only 2 trials) for low back pain despite efficacy in spasticity 3, 2
• Benzodiazepines (diazepam) showed no difference from cyclobenzaprine for global improvement but are not preferred due to abuse potential 3

Combination Therapy

• Adding tizanidine to acetaminophen or an NSAID provides consistently greater short-term pain relief than monotherapy in high-quality trials 3
• Cyclobenzaprine combined with naproxen reduces objective muscle spasm and tenderness more than naproxen alone (P<0.05), though drowsiness increases 6
• Combination therapy increases CNS adverse events (RR 2.44; 95% CI 1.05-5.63) but may reduce gastrointestinal adverse events (RR 0.54; 95% CI 0.26-1.14) 3

Treatment Duration and Monitoring

• Limit muscle relaxant use to 1-2 weeks maximum for acute low back pain 1, 2
• The greatest treatment efficacy occurs in the first 4 days, declining after the first week 5
• Reassess at 2-4 days for acute pain relief 2
• If no improvement after a time-limited course, reassess diagnosis and consider alternative therapies 2

Critical Safety Considerations

Common Adverse Effects:

• All skeletal muscle relaxants increase total adverse events (RR 1.50; 95% CI 1.14-1.98) and CNS adverse events (RR 2.04; 95% CI 1.23-3.37) compared to placebo 3, 7
• Drowsiness/sedation is the most common adverse effect, occurring with all agents 4, 7
• Cyclobenzaprine causes more dry mouth, while diazepam causes more dizziness 4
• Cyclobenzaprine's efficacy is independent of its sedative effects 4, 8

Special Populations:

• Elderly patients: Start cyclobenzaprine at 5 mg and titrate slowly due to doubled AUC and Cmax 4
• Hepatic impairment: Use cyclobenzaprine with caution in mild impairment (5 mg starting dose); avoid in moderate-to-severe impairment 4
• Tizanidine requires monitoring for hepatotoxicity, which is generally reversible 1, 2

Key Clinical Pitfalls

• Avoid carisoprodol due to abuse potential, despite its efficacy 8
• Do not use muscle relaxants for chronic low back pain—only one low-quality trial of cyclobenzaprine exists for chronic pain, with mixed results 3
• No evidence supports one muscle relaxant being superior to others for benefits or harms, except for the limited data on baclofen and dantrolene 3
• Serious complications with muscle relaxants are rare, and most adverse events are self-limited 3