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 injuries [1-12]. 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 diseases [1, 13-16]. 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, 17, 18]. 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): Monotherapy [1-18]
Drug NameDosage Form/StrengthTreatment IndicationMaximum Recommended Dosage
baclofen (generic, Lyvispah, Ozobax DS, Fleqsuvy) 5 mg, 10 mg, 20 mg tablets (generic); 5 mg, 10 mg, 20 mg oral granules (Lyvispah); 5 mg/ 10 mL, 10 mg/ 5 mL oral solution (Ozobax DS, generics); 5 mg/mL oral suspension (Fleqsuvy, generics)spasticity80 mg/day, in divided doses
carisoprodol (Soma, generic)250 mg, 350 mg tabletsmuscle spasm1400 mg/day, in divided doses
chlorzoxazone (generic)250 mg, 375 mg, 500 mg tablets, 750 mg tabletsmuscle spasm3000 mg/day, in divided doses
chlorzoxazone (Lorzone)375 mg, 750 mg tabletsmuscle spasm3000 mg/day, in divided doses
cyclobenzaprine tablet (Fexmid, generic)5 mg, 7.5 mg (Fexmid), 10 mg tabletsmuscle spasm30 mg/day, in divided doses
cyclobenzaprine capsule, extended-release (Amrix, generic)15 mg, 30 mg capsulesmuscle spasm30 mg/day
dantrolene (Dantrium, generic)25 mg, 50 mg, 100 mg capsulesspasticity400 mg/day, in divided doses
metaxalone (Skelaxin, generic)400 mg, 800 mg tabletsmuscle spasm3200 mg/day, in divided doses
methocarbamol (Robaxin, generic)500 mg, 750 mg, 1000 mg tabletsmuscle spasm8 g/day, in divided doses
orphenadrine ER (generic)100 mg extended-release tabletmuscle spasm200 mg/day, in divided doses
tizanidine2 mg, 4 mg tablets (Zanaflex, generic); 2 mg, 4 mg, 6 mg capsules (Zanaflex, generic)spasticity36 mg/day, in divided doses
Table 2. Skeletal Muscle Relaxant Maximum Recommended Dosages (Adults): Combination Therapy [1, 19, 20]
Drug NameDosage Form/StrengthTreatment IndicationMaximum Recommended Dosage 
carisoprodol/ ASA/codeine (generic)200 mg/325 mg/16 mg tabletsacute pain associated with musculoskeletal conditions400 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 tabletsMild to moderate pain of acute musculoskeletal disorders200 mg/3080 mg/240 mg daily

Legend:

  • ASA - aspirin

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 impairment [1, 2].

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 hepatitis [1, 3, 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 impairment [1, 5-8].

Administer baclofen cautiously in patients with renal impairment as the drug is primarily renally excreted [1, 13-16].

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 kidneys [1, 12].

Metaxalone is contraindicated for use in patients with significantly impaired renal and/or hepatic function [1, 9].

Dosage adjustments for methocarbamol may be necessary for patients with hepatic impairment, as the drug is extensively metabolized in the liver [1, 10, 11].

Dantrolene should not be prescribed to patients with hepatic disease due to risk of hepatic injury associated with this drug [1, 18].

Tizanidine is extensively metabolized by the liver and eliminated by the kidneys; therefore, tizanidine should be prescribed cautiously to patients with hepatic and renal impairment [1, 17].