FDA Box Warning
Drug may be hepatotoxic and should be used only for recommended conditions. Daily doses of 400 mg are less likely to cause fatal and nonfatal hepatitis than daily doses above 800 mg. Overt hepatitis is most common during months 3 and 12, but may occur at any time; females, patients older than age 35, and those receiving concurrent therapy are at higher risk. Use only in conjunction with liver monitoring. Monitor liver function at baseline and regularly during therapy. Discontinue drug if values are abnormal.
Use lowest possible effective dose. If no benefit occurs after 45 days, discontinue.
Relaxes skeletal muscle by affecting excitation-contraction coupling response at site beyond myoneural junction, probably by interfering with calcium release from sarcoplasmic reticulum
Capsules: 25 mg, 50 mg, 100 mg
Powder for injection: 20 mg/vial
Indications and dosages
➣ Chronic spasticity resulting from upper motor neuron disorders, such as multiple sclerosis, cerebral palsy, or spinal cord injury
Adults: Initially, 25 mg P.O. daily, increased gradually in 25-mg increments, if needed, up to 100 mg two or three times daily, to a maximum dosage of 400 mg P.O. daily. Maintain dosage level for 4 to 7 days to gauge patient response.
Children: Initially, 0.5 mg/kg P.O. daily for 7 days, increased to 0.5 mg/kg P.O. t.i.d. for 7 days; then 1 mg/kg P.O. t.i.d. for 7 days; then 2 mg/kg t.i.d., as needed. Don't exceed 100 mg P.O. q.i.d.
➣ Malignant hyperthermic crisis
Adults and children: Initially, 1 mg/kg by I.V. push, repeated as needed up to a cumulative dosage of 10 mg/kg/day
➣ To prevent or minimize malignant hyperthermia in patients who require surgery
Adults and children: 4 to 8 mg/kg P.O. daily in three or four divided doses for 1 to 2 days before surgery; give last dose 3 to 4 hours before surgery. Or 2.5 mg/kg I.V. infused over 1 hour before anesthestics are given.
➣ To prevent recurrence of malignant hyperthermic crisis
Adults: 4 to 8 mg/kg daily P.O. in four divided doses for up to 3 days after initial hyperthermic crisis
• Heat stroke
• Neuroleptic malignant syndrome
• Active hepatic disease (oral form)
• Patients who use spasticity to maintain posture or balance (oral form)
Use cautiously in:
• cardiac, hepatic, or respiratory dysfunction or impairment
• women (especially pregnant women)
• adults older than age 35
• children younger than age 5.
• For I.V. use, add 60 ml of sterile water for injection to each vial; shake until solution is clear. Protect from direct light and use within 6 hours.
• Give therapeutic or emergency dose by rapid I.V. push. Administer followup dose over 2 to 3 minutes.
• Prevent extravasation when giving I.V. Drug has high pH and causes tissue irritation.
CNS: dizziness, drowsiness, fatigue, malaise, weakness, confusion, depression, insomnia, nervousness, headache, light-headedness, speech disturbances, seizures
CV: tachycardia, blood pressure fluctuations, phlebitis, heart failure
EENT: double vision, excessive tearing
GI: nausea, vomiting, diarrhea, constipation, abdominal cramps, GI reflux and irritation, hematemesis, difficulty swallowing, anorexia, GI bleeding
GU: urinary frequency, dysuria, nocturia, urinary incontinence, hematuria, crystalluria, prostatitis
Hematologic: aplastic anemia, leukopenia, thrombocytopenia, lymphocytic lymphoma
Musculoskeletal: myalgia, backache
Respiratory: suffocating sensation, respiratory depression, pleural effusion with pericarditis
Skin: rash, urticaria, pruritus, eczemalike eruptions, sweating, photosensitivity, abnormal hair growth
Other: altered taste, chills, fever, edema
Drug-drug. CNS depressants: increased CNS depression
Estrogen: increased risk of hepatotoxicity
Verapamil (I.V.): cardiovascular collapse (when given with I.V. dantrolene)
Drug-diagnostic tests. Alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, bilirubin, blood urea nitrogen: increased values
Drug-behaviors. Alcohol use: increased CNS depression
Sun exposure: phototoxicity
• Obtain baseline liver function test results; monitor periodically during therapy.
• Monitor ECG, serum electrolytes, and urine output regularly.
With long-term oral therapy, monitor patient for signs and symptoms of hepatotoxicity. Be prepared to discontinue drug if these occur.
• Assess for muscle weakness, poor coordination, and reduced reflexes before and during therapy. Drug may weaken muscles and impair ambulation.
Instruct patient receiving prolonged oral therapy to immediately report weakness, malaise, fatigue, nausea, rash, itching, severe diarrhea, bloody or black tarry stools, or yellowing of skin or eyes.
• Inform patient that drug may cause drowsiness, dizziness, or light-headedness.
• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and behaviors mentioned above.