Baclofen

Pronunciation

(BAK loe fen)

U.S. Brand Names

Lioresal®

Generic Available

Yes: Tablets only

Canadian Brand Names

Apo-Baclofen®; Gen-Baclofen; Lioresal®; Liotec; Nu-Baclo; PMS-Baclofen

Use

Treatment of reversible spasticity associated with multiple sclerosis or spinal cord lesions

Orphan drug: Intrathecal: Treatment of intractable spasticity caused by spinal cord injury, multiple sclerosis, and other spinal disease (spinal ischemia or tumor, transverse myelitis, cervical spondylosis, degenerative myelopathy)

Use - Unlabeled/Investigational

Intractable hiccups, intractable pain relief, bladder spasticity, trigeminal neuralgia, cerebral palsy, Huntington's chorea

Pregnancy Risk Factor

Lactation

Enters breast milk (small amounts)/compatible

Contraindications

Hypersensitivity to baclofen or any component of the formulation

Warnings/Precautions

Use with caution in patients with seizure disorder or impaired renal function. Avoid abrupt withdrawal of the drug; abrupt withdrawal of intrathecal baclofen has resulted in severe sequelae (hyperpyrexia, obtundation, rebound/exaggerated spasticity, muscle rigidity, and rhabdomyolysis), leading to organ failure and some fatalities. Risk may be higher in patients with injuries at T-6 or above, history of baclofen withdrawal, or limited ability to communicate. Elderly are more sensitive to the effects of baclofen and are more likely to experience adverse CNS effects at higher doses.

Adverse Reactions

>10%:

Central nervous system: Drowsiness, vertigo, psychiatric disturbances, insomnia, slurred speech, ataxia, hypotonia

Neuromuscular & skeletal: Weakness

1% to 10%:

Cardiovascular: Hypotension

Central nervous system: Fatigue, confusion, headache

Dermatologic: Rash

Gastrointestinal: Nausea, constipation

Genitourinary: Polyuria

<1%: Palpitations, chest pain, syncope, euphoria, excitement, depression, hallucinations, xerostomia, anorexia, abnormal taste, abdominal pain, vomiting, diarrhea, enuresis, urinary retention, dysuria, impotence, inability to ejaculate, nocturia, paresthesia, hematuria, dyspnea

Withdrawal reactions have occurred with abrupt discontinuation (particularly severe with intrathecal use).

Overdosage/Toxicology

Symptoms of overdose include vomiting, muscle hypotonia, salivation, drowsiness, coma, seizures, and respiratory depression. Atropine has been used to improve ventilation, heart rate, blood pressure, and core body temperature. Treatment is symptom-directed and supportive.

For toxicity following intrathecal administration: For adults, administer physostigmine 2 mg I.M. or I.V. (not to exceed 1 mg/minute). For pediatric patients, administer physostigmine 0.02 mg/kg I.M. or I.V. (not to exceed 0.5 mg/minute). Consider withdrawal of 30-40 mL of CSF to reduce baclofen concentration. Abrupt withdrawal of intrathecal baclofen has resulted in severe sequelae (hyperpyrexia, obtundation, muscle rigidity, and rhabdomyolysis)

Drug Interactions

Increased effect: Opiate analgesics, benzodiazepines, hypertensive agents

Increased toxicity: CNS depressants and ethanol (sedation), tricyclic antidepressants (short-term memory loss), clindamycin (neuromuscular blockade), guanabenz (sedation), MAO inhibitors (decrease blood pressure, CNS, and respiratory effects)

Ethanol/Nutrition/Herb Interactions

Ethanol: Avoid ethanol (may increase CNS depression).

Herb/Nutraceutical: Avoid valerian, St John's wort, kava kava, gotu kola.

Compatibility

Stable in sterile, preservative free NS

Compatibility when admixed: Compatible: Morphine

Mechanism of Action

Inhibits the transmission of both monosynaptic and polysynaptic reflexes at the spinal cord level, possibly by hyperpolarization of primary afferent fiber terminals, with resultant relief of muscle spasticity

Pharmacodynamics/Kinetics

Onset of action: 3-4 days

Peak effect: 5-10 days

Absorption (dose dependent): Oral: Rapid

Protein binding: 30%

Metabolism: Hepatic (15% of dose)

Half-life elimination: 3.5 hours

Time to peak, serum: Oral: Within 2-3 hours

Excretion: Urine and feces (85% as unchanged drug)

Dosage

Oral (avoid abrupt withdrawal of drug):

Children:

2-7 years: Initial: 10-15 mg/24 hours divided every 8 hours; titrate dose every 3 days in increments of 5-15 mg/day to a maximum of 40 mg/day

8 years: Maximum: 60 mg/day in 3 divided doses

Adults: 5 mg 3 times/day, may increase 5 mg/dose every 3 days to a maximum of 80 mg/day

Hiccups: Adults: Usual effective dose: 10-20 mg 2-3 times/day

Intrathecal:

Test dose: 50-100 mcg, doses >50 mcg should be given in 25 mcg increments, separated by 24 hours. A screening dose of 25 mcg may be considered in very small patients. Patients not responding to screening dose of 100 mcg should not be considered for chronic infusion/implanted pump.

Maintenance: After positive response to test dose, a maintenance intrathecal infusion can be administered via an implanted intrathecal pump. Initial dose via pump: Infusion at a 24-hour rate dosed at twice the test dose. Avoid abrupt discontinuation.

Elderly: Oral (the lowest effective dose is recommended): Initial: 5 mg 2-3 times/day, increasing gradually as needed; if benefits are not seen withdraw the drug slowly.

Dosing adjustment in renal impairment: It is necessary to reduce dosage in renal impairment but there are no specific guidelines available

Hemodialysis: Poor water solubility allows for accumulation during chronic hemodialysis. Low-dose therapy is recommended. There have been several case reports of accumulation of baclofen resulting in toxicity symptoms (organic brain syndrome, myoclonia, deceleration and steep potentials in EEG) in patients with renal failure who have received normal doses of baclofen.

Administration

Intrathecal: For screening dosages, dilute with preservative-free sodium chloride to a final concentration of 50 mcg/mL for bolus injection into the subarachnoid space; for maintenance infusions, concentrations of 500-2000 mcg/mL may be used

Test Interactions

Increased alkaline phosphatase, AST, glucose, ammonia (B); decreased bilirubin (S)

Patient Education

Take this drug as prescribed. Do not discontinue without consulting prescriber (abrupt discontinuation may cause hallucinations). Do not take any prescription or OTC sleep-inducing drugs, sedatives, or antispasmodics without consulting prescriber. Avoid alcohol use. You may experience transient drowsiness, lethargy, or dizziness; use caution when driving or engaging in tasks requiring alertness until response to drug is known. Frequent small meals or lozenges may reduce GI upset.

Intrathecal use: Keep scheduled pump refill visits; abrupt interruption can cause serious withdrawal symptoms. Report increased spasticity, itching, numbness, unresolved insomnia, painful urination, change in urinary patterns, constipation, high fever, or persistent confusion.

Pregnancy precaution: Inform prescriber if you are or intend to become pregnant.

Nursing Implications

Epileptic patients should be closely monitored; supervise ambulation; avoid abrupt withdrawal of the drug

Anesthesia and Critical Care Concerns/Other Considerations

Avoid abrupt withdrawal of the drug; abrupt withdrawal of intrathecal baclofen has resulted in severe sequelae (hyperpyrexia, obtundation, rebound/exaggerated spasticity, muscle rigidity, and rhabdomyolysis), leading to organ failure and some fatalities. Risk may be higher in patients with injuries at T-6 or above, history of baclofen withdrawal, or limited ability to communicate. Elderly are more sensitive to the effects of baclofen and are more likely to experience adverse CNS effects at higher doses.

Dental Health: Effects on Dental Treatment

No significant effects or complications reported

Dental Health: Vasoconstrictor/Local Anesthetic Precautions

No information available to require special precautions

Mental Health: Effects on Mental Status

Drowsiness and insomnia are common; rare reports of depression, euphoria, and hallucinations

Mental Health: Effects on Psychiatric Treatment

Concurrent use with psychotropics may produce additive sedation; concurrent use with MAO inhibitors may potentiate their hypotensive effects

Dosage Forms

Injection, solution, intrathecal [preservative free] (Lioresal®): 50 mcg/mL (1 mL); 500 mcg/mL (20 mL); 2000 mcg/mL (5 mL)

Tablet: 10 mg, 20 mg

Extemporaneously Prepared

Make a 5 mg/mL suspension by crushing fifteen 20 mg tablets; wet with glycerin, gradually add 45 mL simple syrup in 3 x 5 mL aliquots to make a total volume of 60 mL; refrigerate; stable 35 days

Johnson CE and Hart SM, "Stability of an Extemporaneously Compounded Baclofen Oral Liquid," Am J Hosp Pharm , 1993, 50:2353-5.

References

Abarbanel J, Herishanu Y, Frisher S, "Encephalopathy Associated With Baclofen," Ann Neurol , 1985, 17(6):617-8.

Cooke DE and Glasstone MA, "Baclofen Poisoning in Children," Vet Hum Toxicol , 1994, 36(5):448-50.

Khorasani A and Peruzzi WT, "Dantrolene Treatment for Abrupt Intrathecal Baclofen Withdrawal," Anesth Analg , 1995, 80(5):1054-6.

May CR, "Baclofen Overdose," Ann Emerg Med , 1983, 12:171-3.

Muller-Schwefe G and Penn RD, "Physostigmine in the Treatment of Intrathecal Baclofen Overdose. Report of Three Cases," J Neurosurg , 1989, 71(2):273-5.

Roberge RJ, Martin TG, Hodgman M, et al, "Supraventricular Tachyarrhythmia Associated With Baclofen Overdose," J Toxicol Clin Toxicol , 1994, 32(3):291-7.

Tan AK and Tan CB, "The Syndrome of Painful Legs and Moving Toes...A Case Report," Singapore Med J , 1996, 37(4):446-7.

International Brand Names

Alpha-Baclofen® (NZ); Apo-Baclofen® (CA, NZ, SG); Baclofen AWD® (DE, RO); Baclofen® (CZ, GB, HU, PL, RO, RU); Baclofen dura® (DE); Baclofen Pharmadica® (TH); Baclofen-ratiopharm® (DE, LU); Baclon® (FI); Baclopar® (FI, IE); Baclosal® (IL, TH); Baclospas® (GB); Baklofen NM® (DK); Baklofen NM Pharma® (SE); Baklofen® (NO); Balgifen® (GB); Clofen® (AU); Colmifen® (CY); DBL Baclofen® (AU); Gabalon® (JP); Gen-Baclofen (CA); Lebic® (DE); Lioresal® (AR, AT, AU, BE, BR, CA, CH, DE, DK, ES, FI); Liorésal® (FR); Lioresal® (GB, HK, HR, HU, ID, IE, IL, IN, IT, LU, MT, NL, NO, NZ, PT, RO, SE, SG, TH, TR, ZA); Lioresyl® (CL); Liotec (CA); Norton-Baclofen® (ZA); Nu-Baclo (CA); Pacifen® (NZ); PMS-Baclofen (CA)

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