Muscle Relaxant Guidelines

Introduction to Muscle Relaxants

The American College of Physicians recommends tizanidine as the first alternative for acute musculoskeletal pain 2
Cyclobenzaprine has significant anticholinergic effects, including dry mouth, drowsiness, confusion, urinary retention, and constipation, similar to tricyclic antidepressants 1
Abrupt discontinuation of cyclobenzaprine after long-term use can cause withdrawal symptoms, such as malaise, nausea, and headache, and should be tapered over 2-3 weeks 1

Baclofen is not recommended for routine musculoskeletal pain, as it is primarily an antispasticity agent for upper motor neuron syndromes 2
Baclofen may be considered as second-line for paroxysmal neuropathic pain, with a low initial dose and gradual increase to minimize side effects, such as dizziness, somnolence, and gastrointestinal symptoms 3
Baclofen requires slow tapering when discontinuing after prolonged use to avoid potential delirium and seizures 3

Tizanidine is the strongest evidence-based alternative to cyclobenzaprine, with efficacy demonstrated in 8 trials for acute low back pain, and works through alpha-2 adrenergic agonism 2
Diazepam is particularly inappropriate for older adults due to increased risk of falls, sedation, and anticholinergic effects 2
Methocarbamol, carisoprodol, chlorzoxazone, and metaxalone do not directly relax skeletal muscle, have no evidence of efficacy in chronic pain, and carry significant adverse effect risks in older adults 3, 4

All muscle relaxant trials were 2 weeks or less in duration, and these agents should only be used short-term 2
Insufficient evidence exists for chronic use of any muscle relaxant for musculoskeletal pain 2
Monitor for serotonin syndrome when combining cyclobenzaprine with serotonergic agents, such as SSRIs or SNRIs like venlafaxine 5
Cyclobenzaprine is contraindicated with monoamine oxidase inhibitors, and should be held on the day of surgery due to potential interactions with sedatives and anesthetic agents 1