What are some examples of skeletal muscle relaxers?

Skeletal Muscle Relaxers: Comprehensive List and Classification

Skeletal muscle relaxants comprise two distinct categories: antispasticity agents (baclofen, tizanidine, dantrolene, diazepam) and antispasmodic agents (cyclobenzaprine, carisoprodol, chlorzoxazone, methocarbamol, metaxalone, orphenadrine). 1, 2

Antispasticity Agents

These medications are FDA-approved for spasticity from upper motor neuron syndromes:

• Baclofen - GABA-B receptor agonist used for spasticity from CNS injury and demyelinating conditions 1
• Tizanidine - Most studied antispasticity drug for low back pain, with demonstrated efficacy in 8 trials for acute pain 1, 3
• Dantrolene - Carries a black box warning for potentially fatal hepatotoxicity; sparse evidence for low back pain efficacy 1
• Diazepam - Benzodiazepine with muscle relaxant properties, useful adjunct for skeletal muscle spasm due to reflex spasm or spasticity 4, 2

Antispasmodic Agents

These medications are FDA-approved for musculoskeletal conditions or muscle spasms:

• Cyclobenzaprine - Structurally identical to amitriptyline; most consistently studied with demonstrated efficacy for acute musculoskeletal pain 1, 5
• Carisoprodol - Metabolized to meprobamate (a scheduled drug); removed from European market due to abuse concerns and significant potential for physical/psychological dependence 1, 6
• Chlorzoxazone - Associated with generally reversible hepatotoxicity 1
• Methocarbamol - Limited evidence for musculoskeletal conditions 1, 7
• Metaxalone - Fewest reports of side effects and no major safety issues reported 6, 7
• Orphenadrine - Fair evidence for effectiveness in musculoskeletal conditions 7, 2

Critical Safety Distinctions

All skeletal muscle relaxants increase CNS adverse events (RR 2.04; 95% CI 1.23-3.37) compared to placebo, with sedation being the primary concern. 1, 3

High-Risk Agents Requiring Special Caution:

• Carisoprodol: Greatest concern for dependence and toxicity; avoid due to abuse potential 1, 6
• Dantrolene: Black box warning for potentially fatal hepatotoxicity 1
• Tizanidine and chlorzoxazone: Hepatotoxicity monitoring required, though generally reversible 1
• Cyclobenzaprine: Anticholinergic effects and tricyclic-related toxicity in overdose 1, 6

Evidence-Based Selection Algorithm

For acute musculoskeletal pain: Cyclobenzaprine or tizanidine are preferred first-line options based on consistent efficacy data 1, 3, 7

For spasticity from CNS disorders: Baclofen or tizanidine are roughly equivalent in efficacy, though tizanidine causes more dry mouth and baclofen more weakness 7, 2

For lumbar radiculopathy: Tizanidine is the most effective muscle relaxant option, starting at 2-4mg with upward titration 3

Duration of therapy: Limit to short-term use (7-14 days maximum) as all trials evaluated therapy for 2 weeks or less, with rare exceptions 1, 3

Agents to Avoid

Do not prescribe: Carisoprodol (abuse potential), dantrolene for non-spasticity conditions (hepatotoxicity risk), or any muscle relaxant with the mistaken belief it relieves muscle spasm through direct muscle effects—these drugs act centrally, not peripherally 1, 6