1.1. Adults

The skeletal muscle relaxants (SMRs), carisoprodol, chlorzoxazone, cyclobenzaprine, methocarbamol, metaxalone, and orphenadrine, are FDA-approved for short-term use to manage discomfort associated with acute, painful musculoskeletal conditions such as strains, sprains, and other muscle injuries1-10. These agents should be used as an adjunct to non-pharmacologic treatments, including rest and physical therapy. Baclofen is FDA approved to alleviate signs and symptoms of spasticity resulting from multiple sclerosis, particularly for the relief of flexor spasms and concomitant pain, clonus, and muscular rigidity. Baclofen may also be useful in patients with spinal cord injuries and other spinal cord diseases1,2,11-14. Tizanidine is FDA approved for the management of spasticity, and dantrolene is FDA approved for managing spasticity due to upper motor neuron disorders (e.g., spinal cord injury, cerebral palsy, multiple sclerosis, or stroke)1,2,15,16. Maximum recommended dosages for SMRs are summarized in Table 1. Dosages exceeding these recommendations will be reviewed.

Table 1. Skeletal Muscle Relaxant Maximum Recommended Dosages (Adults): Monotherapy1-16
Drug Name Dosage Form/Strength Treatment Indication Maximum Recommended Dosage
baclofen (generic, Lyvispah®, Ozobax®, Fleqsuvy®) 5 mg, 10 mg, 20 mg tablets (generic); 5 mg, 10 mg, 20 mg oral granules (Lyvispah®); 5 mg/ 5 mL oral solution (Ozobax®, generic); 5 mg/mL oral suspension (Fleqsuvy®) spasticity 80 mg/day, in divided doses
carisoprodol (Soma®, generic) 250 mg, 350 mg tablets muscle spasm 1400 mg/day, in divided doses
chlorzoxazone (generic) 250 mg, 375 mg, 500 mg tablets, 750 mg tablets muscle spasm 3000 mg/day, in divided doses
chlorzoxazone (Lorzone®) 375 mg, 750 mg tablets muscle spasm 3000 mg/day, in divided doses
cyclobenzaprine tablet (Fexmid®, generic) 5 mg, 7.5 mg (Fexmid®), 10 mg tablets muscle spasm 30 mg/day, in divided doses
cyclobenzaprine capsule, extended-release (Amrix®, generic) 15 mg, 30 mg capsules muscle spasm 30 mg/day
dantrolene (Dantrium®, generic) 25 mg, 50 mg, 100 mg capsules spasticity 400 mg/day, in divided doses
metaxalone (Skelaxin®, generic) 400 mg, 800 mg tablets muscle spasm 3200 mg/day, in divided doses
methocarbamol (Robaxin®, generic) 500 mg, 750 mg tablets muscle spasm 8 g/day, in divided doses
orphenadrine ER (generic) 100 mg extended-release tablet muscle spasm 200 mg/day, in divided doses
tizanidine 2 mg, 4 mg tablets (Zanaflex®, generic); 2 mg, 4 mg, 6 mg capsules (Zanaflex®, generic) spasticity 36 mg/day, in divided doses
Table 2. Skeletal Muscle Relaxant Maximum Recommended Dosages (Adults): Combination Therapy1,2,17,18
Drug Name Dosage Form/Strength Treatment Indication Maximum Recommended Dosage 
carisoprodol/ ASA/codeine (generic) 200 mg/325 mg/16 mg tablets acute pain associated with musculoskeletal conditions 400 mg/650 mg/32 mg (2 tablets) four times daily
orphenadrine/ ASA/ caffeine (Norgesic Forte®, generic) 25 mg/385 mg/30 mg, 50 mg/770 mg/60 mg tablets Mild to moderate pain of acute musculoskeletal disorders 200 mg/3080 mg/240 mg daily

Legend:

  • ASA - aspirin

1.1.1. Dosing in Renal and Hepatic Disease

Carisoprodol dosing adjustments should be considered for patients with severe hepatic insufficiency, as carisoprodol is extensively metabolized by the liver. Carisoprodol is also renally eliminated and should be dosed cautiously in patients with severe renal impairment1-3 .

Chlorzoxazone should be administered cautiously, if at all, in patients with a history of hepatic disease as hepatotoxicity has been reported with chlorzoxazone use. Chlorzoxazone should not be prescribed to patients with active hepatic disease, including hepatitis1,2,4 .

Cyclobenzaprine is extensively metabolized by liver and is not recommended for use in patients with moderate to severe hepatic impairment. Cyclobenzaprine dosage adjustments are necessary in patients with mild hepatic impairment1,2,5-7 .

Administer baclofen cautiously in patients with renal impairment as the drug is primarily renally excreted1,2,11 .

Orphenadrine should be administered cautiously to patients with renal and hepatic disease, as the drug is extensively metabolized in the liver, with metabolites and unchanged drug eliminated by the kidneys1,2,10 .

Dosage adjustments for methocarbamol may be necessary for patients with hepatic impairment, as the drug is extensively metabolized in the liver1,2,9 .

Metaxalone is contraindicated for use in patients with significantly impaired renal and/or hepatic function1,2.

Dantrolene should not be prescribed to patients with hepatic disease due to risk of hepatic injury associated with this drug1,2,16.

Tizanidine is extensively metabolized by the liver and eliminated by the kidneys; therefore, tizanidine should be prescribed cautiously to patients with hepatic and renal impairment1,2,15< ./p>

1.2. Pediatrics

With the exception of dantrolene, skeletal muscle relaxants are not FDA-approved for use in children1,2,16. Safety and efficacy of cyclobenzaprine extended-release capsules (Amrix®) have not been evaluated in pediatric patients, including adolescents1,2,7. Select skeletal muscle relaxants are FDA-approved for use in adolescents. Recommended pediatric dosages and age limitations for skeletal muscle relaxants are summarized in Table 2.

Although not FDA-approved, baclofen has been used for spasticity in pediatric patients 2 to 7 years of age in doses up to 40 mg/day and in children 8 to 11 years of age in maximum doses of 60 mg/day1.

Table 3. Maximum Recommended Dosages for Skeletal Muscle Relaxants (Pediatric Patients)
Drug Name Treatment Indication Maximum Recommended Dosage
baclofen spasticity Greater than or equal to 12 years of age: 80 mg/day, in divided doses
dantrolene spasticity Greater than or equal to 5 years of age: 400 mg/day, in divided doses
carisoprodol muscle spasm Greater than or equal to 16 years of age: 1400 mg/day, in divided doses
cyclobenzaprine tablets muscle spasm Greater than or equal to 15 years of age: 30 mg/day, in divided doses
metaxalone muscle spasm Greater than 12 years of age: 3200 mg/day, in divided doses
methocarbamol muscle spasm Greater than or equal to 16 years of age: 8 g/day, in divided doses