Muscle Relaxant Dosing
For cyclobenzaprine, start with 5 mg three times daily, which provides equivalent efficacy to 10 mg three times daily but with significantly less sedation, and limit use to 2-3 weeks maximum. 1
Cyclobenzaprine Dosing
Standard Dosing
- Initial dose: 5 mg three times daily (TID) 1
- May increase to 10 mg TID based on individual response, though the 5 mg dose is equally effective with better tolerability 1, 2
- Maximum recommended duration: 2-3 weeks 1
Special Populations
- Hepatically impaired patients: Start with 5 mg and titrate slowly upward; avoid use in moderate to severe hepatic impairment 1
- Elderly patients: Use less frequent dosing, starting with 5 mg 1
Clinical Evidence for Lower Dosing
- The 5 mg TID regimen demonstrated statistically significant superiority over placebo for all primary endpoints (global impression of change, medication helpfulness, relief from backache) at days 3-4 and day 8 2
- Efficacy was independent of sedation—patients who did not report somnolence still experienced meaningful treatment effects 2
- The 2.5 mg TID dose was not significantly more effective than placebo and should not be used 2
Important Caveats
- Cyclobenzaprine monotherapy is as effective as combination therapy with ibuprofen—adding ibuprofen 400-800 mg TID provides no additional benefit 3
- Recent evidence suggests SMRs including cyclobenzaprine may not improve outcomes more than placebo when combined with NSAIDs for acute low back pain 4
- Structurally related to tricyclic antidepressants with significant anticholinergic effects (dry mouth, drowsiness, confusion, urinary retention, constipation) 5
- Abrupt discontinuation after long-term use can cause withdrawal symptoms (malaise, nausea, headache)—taper over 2-3 weeks if used chronically 5
Baclofen Dosing
Clinical Context
- Baclofen is NOT recommended for routine musculoskeletal pain—it is primarily an antispasticity agent for upper motor neuron syndromes 6
- Only sparse evidence supports its use for low back pain 6
- May be considered as second-line for paroxysmal neuropathic pain 7
Dosing When Indicated
- Start with a low dose and gradually increase to minimize side effects (dizziness, somnolence, gastrointestinal symptoms) 7
- Specific dosing not provided in musculoskeletal pain guidelines due to limited evidence 7
- Requires slow tapering when discontinuing after prolonged use to avoid potential delirium and seizures 7
Alternative Muscle Relaxants
Tizanidine (Preferred Alternative)
- Tizanidine is the strongest evidence-based alternative to cyclobenzaprine, with efficacy demonstrated in 8 trials for acute low back pain 6
- Works through alpha-2 adrenergic agonism (different mechanism than cyclobenzaprine), which may provide benefit when cyclobenzaprine fails 6
- The American College of Physicians recommends tizanidine as the first alternative for acute musculoskeletal pain 6
Agents to Avoid
- Diazepam: Particularly inappropriate for older adults due to increased risk of falls, sedation, and anticholinergic effects 6
- Methocarbamol, carisoprodol, chlorzoxazone, metaxalone: These "muscle relaxants" do not directly relax skeletal muscle, have no evidence of efficacy in chronic pain, and carry significant adverse effect risks in older adults 7
- Carisoprodol has been removed from the European market due to abuse concerns 7
Critical Clinical Considerations
Duration of Therapy
- All muscle relaxant trials were 2 weeks or less in duration—these agents should only be used short-term 6
- Insufficient evidence exists for chronic use of any muscle relaxant for musculoskeletal pain 6
Adverse Effects
- All skeletal muscle relaxants are associated with higher rates of CNS adverse events compared to placebo, including drowsiness and dizziness 6
- Somnolence and dry mouth are the most common adverse effects with cyclobenzaprine, occurring in a dose-dependent manner 2
- Cyclobenzaprine exhibits high-affinity noncompetitive antagonism at histamine H1 receptors, which likely explains its significant sedative effects 8