Classifications: central-acting skeletal muscle relaxant;
Therapeutic:central-acting skeletal muscle relaxant; antispasmodic

Prototype: Cyclobenzaprine
Pregnancy Category: C


25 mg, 50 mg, 100 mg capsules; 20 mg vial


Hydantoin derivative with peripheral skeletal muscle relaxant action. Directly relaxes the spastic muscle by interfering with calcium ion release from sarcoplasmic reticulum within skeletal muscle. Clinical doses produce about a 50% decrease in contractility of skeletal muscles.

Therapeutic Effect

Relief of muscle spasticity, however, may be accompanied by muscle weakness sufficient to affect overall functional capacity of the patient.


Orally for the symptomatic treatment of skeletal muscle spasms secondary to spinal cord injury, stroke, cerebral palsy, multiple sclerosis. Used intravenously for the management of malignant hyperthermia. Oral dantrolene can be used prophylactically for patients with a history of malignant hyperthermia or with a family history of the disorder.

Unlabeled Uses

Neuroleptic malignant syndrome, exercise-induced muscle pain, and flexor spasms.


Active hepatic disease; when spasticity is necessary to sustain upright posture and balance in locomotion or to maintain increased body function; spasticity due to rheumatic disorders; pregnancy (category C), lactation. Safe use in children <5 y is not established.

Cautious Use

Impaired cardiac or pulmonary function, muscular sclerosis; neuromuscular disease; myopathy; patients >35 y, especially women.

Route & Dosage

Relief of Spasticity
Adult: PO 25 mg once/d, increase to 25 mg b.i.d. to q.i.d., may increase q4–7d up to 100 mg b.i.d. to q.i.d.
Child: PO 0.5 mg/kg b.i.d., increase to 0.5 mg/kg t.i.d. or q.i.d., may increase by 0.5 mg/kg up to 3 mg/kg b.i.d. to q.i.d. (max: 100 mg q.i.d.)

Malignant Hyperthermia Treatment
Adult/Child: IV 1 mg/kg rapid direct IV push repeated prn up to a total of 10 mg/kg PO May be necessary to continue orally with 1–2 mg/kg q.i.d. for 1–3 d to prevent recurrence

Malignant Hyperthermia Prophylaxis
Adult: IV 1.5 mg/kg infusion over 1 h may be repeated

Hepatic Impairment
Do not use in active liver disease.


  • Prepare oral suspension for a single dose, when necessary, by emptying contents of capsule(s) into fruit juice or other liquid. Shake suspension well before pouring. Avoid contamination, keep refrigerated, and use within several days, since it will not contain a preservative.

PREPARE: Direct: Dilute each 20 mg with 60 mL sterile water without preservatives. Shake until clear.  

ADMINISTER: Direct: Give by rapid direct IV push. Avoid extravasation; solution has a high pH and therefore is extremely irritating to tissue. Ensure IV patency prior to IV push.  

  • Store capsules in tightly closed, light-resistant container. Contents of vial (for IV use) must be protected from direct light and used within 6 h after reconstitution, since it does not contain a preservative. Store both PO and parenteral forms at 15°–30° C (59°–86° F) unless otherwise directed.

Adverse Effects (≥1%)

Body as a Whole: Hypersensitivity (pruritus, urticaria, eczematoid skin eruption, photosensitivity, eosinophilic pleural effusion). CNS: Drowsiness, muscle weakness, dizziness, light-headedness, unusual fatigue, speech disturbances, headache, confusion, nervousness, mental depression, insomnia, euphoria, seizures. CV: Tachycardia, erratic BP. Special Senses: Blurred vision, diplopia, photophobia. GI: Diarrhea, constipation, nausea, vomiting, anorexia, swallowing difficulty, alterations of taste, gastric irritation, abdominal cramps, GI bleeding; hepatitis, jaundice, hepatomegaly, hepatic necrosis (all related to prolonged use of high doses). Urogenital: Crystalluria with pain or burning with urination, urinary frequency, urinary retention, nocturia, enuresis, difficult erection.


Drug: Alcohol and other cns depressants compound CNS depression; estrogens increase risk of hepatotoxicity in women >35 y; verapamil and other calcium channel blockers increase risk of ventricular fibrillation and cardiovascular collapse with IV dantrolene.


Absorption: Incompletely absorbed from GI tract. Peak: 5 h. Distribution: Crosses placenta. Metabolism: In liver. Elimination: In urine chiefly as metabolites. Half-Life: 8.7 h.

Nursing Implications

Assessment & Drug Effects

  • Monitor for therapeutic effectiveness. Improvement may not be apparent until 1 wk or more of drug therapy.
  • Monitor vital signs during IV infusion. Also monitor ECG, CVP, and serum potassium.
  • Supervise ambulation until patient's reaction to drug is known. Relief of spasticity may be accompanied by some loss of strength.
  • Note: Most common adverse effects are generally transient, lasting up to 14 d after initiation of therapy. Keep physician informed.
  • Monitor patients with impaired cardiac or pulmonary function closely for cardiovascular or respiratory symptoms such as tachycardia, BP changes, feeling of suffocation.
  • Monitor for and report symptoms of allergy and allergic pleural effusion: Shortness of breath, pleuritic pain, dry cough.
  • Alert physician if improvement is not evident within 45 d. Drug may be discontinued because of the possibility of hepatotoxicity (see Appendix F).
  • Lab tests: Perform baseline and regularly scheduled hepatic function tests (alkaline phosphatase, AST, ALT, total bilirubin), blood cell counts, and renal function tests.
  • Monitor bowel function. Persistent diarrhea may necessitate drug withdrawal. Severe constipation with abdominal distention and signs of intestinal obstruction have been reported.

Patient & Family Education

  • Report promptly the onset of jaundice: yellow skin or sclerae; dark urine, clay-colored stools, itching, abdominal discomfort. Hepatotoxicity frequently occurs between 3rd and 12th mo of therapy.
  • Do not drive or engage in other potentially hazardous activities until response to drug is known.
  • Do not use OTC medications, alcoholic beverages, or other CNS depressants unless otherwise advised by physician. Liver toxicity occurs more commonly when other drugs are taken concurrently.

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

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