Classifications: centrally acting skeletal muscle relaxant;
Therapeutic: skeletal muscle relaxer; antispasmodic

Prototype: Cyclobenzaprine
Pregnancy Category: C


250 mg, 500 mg tablets


Centrally acting skeletal muscle relaxant. Acts indirectly by depressing nerve transmission through polysynaptic pathways in spinal cord, subcortical centers, and brainstem; also possibly has a sedative effect.

Therapeutic Effect

Effectively controls muscle spasms and pain associated with musculoskeletal conditions. Not effective for spastic or dyskinetic CNS disorders (e.g., cerebral palsy).


Symptomatic treatment of muscle spasm and pain associated with various musculoskeletal conditions.


Impaired liver function; alcoholism; hepatic disease, jaundice; pregnancy (category C).

Cautious Use

Patients with known allergies or history of drug allergies; renal impairment or failure; CNS depression; older adult patients, lactation.

Route & Dosage

Skeletal Muscle Relaxant
Adult: PO 250–500 mg t.i.d. or q.i.d. (max: 3 g/d)
Child: PO 20 mg/kg/d in 3–4 divided doses


  • Give with food or meals to prevent gastric distress. If necessary, tablet may be crushed and mixed with food or liquid (e.g., milk, fruit juice).
  • Store in tight container at 15°–30° C (59°–86° F) unless otherwise directed.

Adverse Effects (≥1%)

GI: Anorexia, heartburn, nausea, vomiting, constipation, diarrhea, abdominal pain, hepatotoxicity: jaundice, liver damage. CNS: Drowsiness, dizziness, light-headedness, headache, malaise, overstimulation. Skin: Erythema, rash, pruritus, urticaria, petechiae, ecchymoses.


Drug: Alcohol, cns depressants add to CNS depression.


Absorption: Readily absorbed from GI tract. Onset: 1 h. Peak: 1–4 h. Duration: 3–4 h. Distribution: Not known if crosses placenta or distributed into breast milk. Metabolism: In liver. Elimination: In urine. Half-Life: 66 min.

Nursing Implications

Assessment & Drug Effects

  • Monitor ambulation during early drug therapy; some patients may require supervision.
  • Lab tests: Periodic liver function tests are advised in patients receiving long-term therapy even if sporadic.
  • Note: Since chlorzoxazone metabolite may discolor urine, dark urine cannot be a reliable sign of a hepatotoxic reaction.

Patient & Family Education

  • Avoid activities requiring mental alertness, judgment, and physical coordination until reaction to drug is known, since sedation, drowsiness, and dizziness may occur.
  • Drug may discolor urine orange to purplish red, but this is of no clinical significance.
  • Discontinue drug and notify physician if signs of hypersensitivity (see Appendix F) or of liver dysfunction appear (abdominal discomfort, yellow sclerae or skin, pruritus, malaise, nausea, vomiting).
  • Check with physician before taking an OTC depressant (e.g., antihistamine, sedative, alcohol) since effects may be additive.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2023 Last Updated On: 02/01/2023 (0)
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