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a skeletal muscle relaxant producing its effect primarily on the myoneural junction and the muscle tissue, and only secondarily on the central nervous system. It is used as the sodium salt, administered orally as an antispasmodic in conditions such as stroke, multiple sclerosis, and cerebral palsy; it is also used orally or intravenously in the prophylaxis and treatment of malignant hyperthermia.
Pregnancy Category: C
ClassificationTherapeutic: skeletal muscle relaxants
Oral: Treatment of spasticity associated with:
- Spinal cord injury,
- cerebral palsy,
- multiple sclerosis.
Acts directly on skeletal muscle, causing relaxation by decreasing calcium release from sarcoplasmic reticulum in muscle cells.
Prevents intense catabolic process associated with malignant hyperthermia.
Reduction of muscle spasticity.
Prevention of malignant hyperthermia.
Absorption: 35% absorbed after oral administration.
Metabolism and Excretion: Almost entirely metabolized by the liver.
Half-life: 8.7 hr.
Time/action profile (effects on spasticity)
|PO||1 wk||unknown||6–12 hr|
Contraindicated in: No contraindications to IV form in treatment of hyperthermia; Lactation: LactationSituations in which spasticity is used to maintain posture or balance.
Use Cautiously in: Cardiac, pulmonary, or previous liver disease;Women and patients >35 yr (↑ risk of hepatotoxicity); Geriatric: Use lowest possible dose (may have ↑ risk of hepatotoxicity) Obstetric: Use only if benefit outweighs potential risk to fetus
Adverse Reactions/Side Effects
Central nervous system
- drowsiness (most frequent)
- muscle weakness (most frequent)
Ear, Eye, Nose, Throat
- excessive lacrimation
- visual disturbances
- pleural effusions
- respiratory depression
- changes in BP
- heart failure
- hepatotoxicity (life-threatening)
- diarrhea (most frequent)
- GI bleeding
- erectile dysfunction
- aplastic anemia
- irritation at IV site
- anaphylaxis (life-threatening)
Drug-Drug interactionAdditive CNS depression with CNS depressants, including alcohol, antihistamines, opioid analgesics, sedative/hypnotics, and parenteral magnesium sulfate.↑ risk of hepatotoxicity with other hepatotoxic agents or estrogens.↑ risk of arrhythmias with verapamil.↑ neuromuscular blocking effects of vecuronium.Concomitant use of kava-kava, valerian, chamomile, or hops can ↑ CNS depression.
Oral (Adults) Spasticity—25 mg once daily for 7 days, then 25 mg 2 times daily for 7 days, then 50 mg 3 times daily for 7 days, then 100 mg 3 times daily; may ↑ to 100 mg 4 times daily, if needed. Prevention of malignant hyperthermia—4–8 mg/kg/day in 3–4 divided doses for 1–2 days before procedure, last dose 3–4 hr preop. Posthyperthermic crisis follow-up—4–8 mg/kg/day in 3–4 divided doses for 1–3 days after IV treatment.
Oral (Children >5 yr) Spasticity—0.5 mg/kg once daily for 7 days, then 0.5 mg/kg 3 times daily for 7 days, then 1 mg/kg 3 times daily for 7 days, then 2 mg/kg 3 times daily (not to exceed 400 mg/day). Prevention of malignant hyperthermia—4–8 mg/kg/day in 3–4 divided doses for 1–2 days before procedure, last dose 3–4 hr preop. Posthyperthermic crisis follow-up—4–8 mg/kg/day in 3–4 divided doses for 1–3 days after IV treatment.
Intravenous (Adults and Children) Treatment of malignant hyperthermia—at least 1 mg/kg (up to 3 mg/kg), continued until symptoms decrease or a cumulative dose of 10 mg/kg has been given. If symptoms reappear, dose may be repeated. Prevention of malignant hyperthermia—2.5 mg/kg before anesthesia.
Availability (generic available)
Capsules: 25 mg, 50 mg, 100 mg
Powder for injection: 20 mg/vial
- Assess bowel function periodically. Persistent diarrhea may warrant discontinuation of therapy.
- Muscle Spasticity: Assess neuromuscular status and muscle spasticity before initiating and periodically during therapy to determine response.
- Malignant Hyperthermia: Assess previous anesthesia history of all surgical patients. Also assess for family history of reactions to anesthesia (malignant hyperthermia or perioperative death).
- Monitor ECG, vital signs, electrolytes, and urine output continuously when administering IV for malignant hyperthermia.
- Monitor patient for difficulty swallowing and choking during meals on the day of administration.
- Lab Test Considerations: Monitor liver function frequently during therapy. Liver function abnormalities (↑ AST, ALT, alkaline phosphatase, bilirubin, GGTP) may require discontinuation of therapy.
- Evaluate renal function and CBC before and periodically during therapy in patients receiving prolonged therapy.
Potential Nursing DiagnosesImpaired physical mobility (Indications)
Acute pain (Indications)
Risk for injury (Side Effects)
- Oral: If gastric irritation becomes a problem, may be administered with food. Oral suspensions may be made by opening capsules and adding them to fruit juices or other liquids. Drink immediately after mixing.
- Oral dose for spasticity should be divided into 4 doses/day.
- Oral dose is not indicated for neuroleptic malignant syndrome.
- pH: No Data.
- Diluent: Reconstitute each 20 mg with 60 mL of sterile water for injection (without a bacteriostatic agent). Shake until solution is clear. Solution must be used within 6 hr. Administer without further dilution. Protect diluted solution from direct light.Concentration: 0.333 mg/mL.
- Rate: Administer each single dose by rapid continuous IV push through Y-tubing or 3-way stopcock. Follow immediately with subsequent doses as indicated. Medication is very irritating to tissues; observe infusion site frequently to avoid extravasation.
- Intermittent Infusion: Prophylactic dose has been administered as an infusion.
- Rate: Administer over 1 hr before anesthesia.
- Y-Site Compatibility: acyclovir, paclitaxel, palonosetron
- Y-Site Incompatibility: alemtuzumab, alfentanil, amikacin, aminophylline, amphotericin B colloidal, amphotericin B lipid complex, ampicillin, ampicillin/sulbactam, anidulafungin, argatroban, arsenic trioxide, ascorbic acid, atracurium, atropine, azathioprine, aztreonam, benztropine, bivalirudin, bleomycin, bumetanide, buprenorphine, butorphanol, caclium chloride, calcium gluconate, carmustine, caspofungin, cefoperazone, cefotaxime, cefotetan, cefoxitin, ceftazidime, ceftriaxone, cefuroxime, chloramphenicol, chlorpromazine, cisplatin, clindamycin, cyanocobalamin, cyclosporine, dactinomycin, daptomycin, dexamethasone, diazepam, diazoxide, digoxin, diltiazem, diphenhydramine, dobutamine, docetaxel, dopamine, doxorubicin liposome, doxycycline, enalaprilat, ephedrine, epinephrine, epoetin alfa, ertapenem, erythromycin, esmolol, etoposide, etoposide phosphate, famotidine, fenoldopam, fentanyl, fluconazole, fludarabine, folic acid, foscarnet, furosemide, ganciclovir, gemcitabine, gentamicin, glycopyrrolate, granisetron, haloperidol, heparin, hetastarch, hydralazine, hydrocortisone, hydromorphone, hydroxyzine, idarubicin, imipenem/cilastatin, indomethacin, insulin, irinotecan, isoproterenol, ketorolac, labetalol, leucovorin, lidocaine, linezolid, lorazepam, magnesium sulfate, mannitol, mechlorethamine, meperidine, metaraminol, methyldopate, methylprednisolone, metoclopramide, metoprolol, metronidazole, midazolam, milrinone, mitoxantrone, morphine, multivitamins, mycophenolate, nafcillin, nalbuphine, naloxone, nesiritide, nitroglycerin, nitroprusside, norepinephrine, octreotide, ondansetron, oxacillin, oxaliplatin, oxytocin, pamidronate, pancuronium, pantoprazole, papaverine, pemetrexed, penicillin G, pentamidine, pentazocine, pentobarbital, phenobarbital, phentolamine, phenylephrine, phenytoin, phytonadione, piperacillin/tazobactam, potassium acetate, potassium chloride, procainamide, prochlorperazine, proimethazine, propranolol, protamine, pyridoxime, ranitidine, sodium acetate, sodium bicarbonate, streptokinase, succinylcholine, sufentanil, tacrolimus, teniposide, theophylline, thiamine, thiotepa, ticarcillin/clavulanate, tigecycline, tirofiban, tobramycin, tolazoline, trimethoprim/sulfamethoxazole, vancomycin, vasopressin, vecuronium, verapamil, vinblastine, vinorelbine, voriconazole, zoledronic acid
- Advise patient not to take more medication than the amount prescribed, to minimize risk of hepatotoxicity and other side effects. If a dose is missed, do not take unless remembered within 1 hr. Do not double doses.
- May cause dizziness, drowsiness, visual disturbances, and muscle weakness. Advise patient to avoid driving and other activities requiring alertness until response to drug is known. After IV dose for surgery, patients may experience decreased grip strength, leg weakness, light-headedness, and difficulty swallowing for up to 48 hr. Caution patients to avoid activities requiring alertness and to use caution when walking down stairs and eating during this period.
- Advise patient to avoid taking alcohol or other CNS depressants concurrently with this medication.
- Instruct patient to notify health care professional if rash; itching; yellow eyes or skin; dark urine; or clay-colored, bloody, or black, tarry stools occur or if nausea, weakness, malaise, fatigue, or diarrhea persists. May require discontinuation of therapy.
- Advise patient to wear sunscreen and protective clothing to prevent photosensitivity reactions.
- Emphasize the importance of follow-up exams to check progress in long-term therapy and blood tests to monitor for side effects.
- Malignant Hyperthermia: Patients with malignant hyperthemia should carry identification describing disease process at all times.
- Relief of muscle spasm in musculoskeletal conditions. One wk or more may be required to see improvement; if there is no observed improvement in 45 days, the medication is usually discontinued.
- Prevention of or decrease in temperature and skeletal rigidity in malignant hyperthermia.