Baclofen
Baclofen (Lioresal)
Baclofen
( BAK-low-fen)
Pregnancy Category: C Apo-Baclofen Dom-Baclofen Gen-Baclofen Lioresal Lioresal Intrathecal Med-Baclofen Novo-Baclofen Nu-Baclo PMS-Baclofen (Rx)

Classification: Skeletal muscle relaxant, centrally acting

See Also: See also Skeletal Muscle Relaxants, Centrally Acting .

Action/Kinetics: Related chemically to GABA, an inhibitory neurotransmitter. May act by combining with the GABA _B receptor subtype. It increases threshold for excitation of primary afferent nerves and decreases the release of excitatory amino acids from presynaptic sites. May also act at certain brain sites. Has CNS depressant effects. After PO use, baclofen is rapidly and extensively absorbed. Peak serum levels PO: 2-3 hr. Therapeutic serum levels: 80-400 ng/mL. t 1/2, PO: 3-4 hr. Onset after intrathecal bolus: 30-60 min; peak effect after intrathecal bolus: 4 hr; duration after intrathecal bolus: 4-8 hr. t 1/2 after bolus lumbar injection of 50 or 100 mcg: 1.5 hr over the first 4 hr. Onset after intrathecal continuous infusion: 6-8 hr; peak effect after intrathecal continuous infusion: 24-48 hr. Seventy percent to 80% of the drug is eliminated unchanged by the kidney.

Uses: PO. Multiple sclerosis (flexor spasms, pain, clonus, and muscular rigidity) and diseases and injuries of the spinal cord associated with spasticity. Not effective for the treatment of cerebral palsy, stroke, parkinsonism, or rheumatic disorders. Investigational: Trigeminal neuralgia, tardive dyskinesia, intractable hiccoughs.
Intrathecal. Severe spasticity of spinal cord of cerebral origin in clients unresponsive to PO baclofen therapy or who have intolerable CNS side effects. Investigational: Reduce spasticity in children with cerebral palsy.

Contraindications: Hypersensitivity. PO used to treat rheumatic disorders, spasm resulting from Parkinson's disease, stroke, cerebral palsy. Intrathecal product for IV, IM, SC, or epidural use.

Special Concerns: Use during lactation only if potential benefit outweighs the potential risk. Safe use of the oral product for children under 12 years of age and of the intrathecal product for children under 4 years of age has not been established. Use with caution in impaired renal function, in those with autonomic dysreflexia and where spasticity is used to sustain an upright posture and balance in locomotion; in those with psychotic disorders, schizophrenia, or confusional states as worsening of these conditions has occurred following PO use. Geriatric clients may be at higher risk for developing CNS toxicity, including mental depression, confusion, hallucinations, and significant sedation. Due to serious, life-threatening side effects after intrathecal use, physicians must be trained and educated in chronic intrathecal infusion therapy. Abrupt drug withdrawal may cause hallucinations and seizures.

Side Effects: CNS: Drowsiness, dizziness, lightheadedness, weakness, lethargy, fatigue, confusion, headaches, insomnia, euphoria, excitement, depression, paresthesia, muscle pain, coordination disorder, tremor, ridigity, dystonia, ataxia, strabismus, dysarthria. Hallucinations following abrupt withdrawal. CV: Hypotension. Rarely, chest pain, syncope, palpitations. GI: N&V, constipation, dry mouth, anorexia, taste disorder, abdominal pain, diarrhea. GU: Urinary frequency, enuresis, urinary retention, dysuria, impotence, inability to ejaculate, nocturia. Ophthalmic: Nystagmus, miosis, mydriasis, diplopia. Miscellaneous: Rash, pruritus, ankle edema, increased perspiration, weight gain, dyspnea, nasal congestion.
Intrathecal, spasticity of spinal origin. CNS: Dizziness, somnolence, paresthesia, headache, convulsion confusion, speech disorder, coma, death insomnia, anxiety, depression, hallucinations. GI: N&V, constipation, dry mouth, diarrhea, anorexia. GU: Urinary retention, impotence, urinary incontinence, urinary frequency. CV: Hypotension, hypertension. Miscellaneous: Accidental injury, asthenia, amblyopia, pain, peripheral edema, dyspnea, hypoventilation, fever, urticaria, anorexia, diplopia, dysautonomia.

Intrathecal, spasticity of cerebral origin. CNS: Somnolence, headache, convulsion dizziness, paresthesia, abnormal thinking, agitation, coma, speech disorder, tremor. GI: N&V, increased salivation, constipation, dry mouth. GU: Urinary retention, urinary incontinence, impaired urination. Miscellaneous: Hypertonia, hypoventilation, hypotension, back pain, pain, pruritus, peripheral edema, asthenia, chills, pneumonia.

Laboratory Test Alterations: AST, alkaline phosphatase, blood glucose.

Overdose Management: Symptoms: Symptoms after PO use include vomiting, drowsiness, muscular hypotonia, muscle twitching, accommodation disorders, respiratory depression, seizures, coma. Symptoms after intrathecal use include drowsiness, dizziness, lightheadedness, somnolence, respiratory depression, rostral progression of hypotonia, seizures, loss of consciousness leading to coma (for up to 24 hr). Treatment:

1. After PO use: Induce vomiting (only if the client is alert and conscious) followed by gastric lavage. If the client is not alert and conscious, undertake only gastric lavage making sure the airway is secured with a cuffed ET tube. Maintain an adequate airway. Atropine may be used to improve HR, BP, ventilation, and core body temperature.

2. After intrathecal use: The residual solution is to be removed from the pump as soon as possible. Intubate the client with respiratory depression until the drug is eliminated. IV physostigmine (total dose of 1-2 mg given over 5-10 min) may be tried, with caution. Consideration can also be given to withdrawing 30-60 mL of CSF to decrease baclofen levels (provided that lumbar puncture is not contraindicated).

Drug Interactions: CNS depressants / Additive CNS depression MAO Inhibitors / CNS depression and hypotension Ticyclic antidepressants / Muscle hypotonia

How Supplied: Kit: 0.05 mg/mL, 0.5 mg/mL, 2 mg/mL; Tablet: 10 mg, 20 mg

Dosage
?Tablets Muscle relaxant, spasticity.
Adults, initial: 5 mg t.i.d. for 3 days; then, 10 mg t.i.d. for 3 days, 15 mg t.i.d. for 3 days, and 20 mg t.i.d. Additional increases in dose may be required but should not exceed 20 mg q.i.d. Maximum daily dose for spasticity should not exceed 260 mg. Children (treatment of spasticity), initial: 10-15 mg/kg/day in 3 divided doses. Titrate to a maximum of 40 mg/day if less than 8 years of age and to a maximum of 80 mg/day if more than 8 years of age.
Trigeminal neuralgia.
50-60 mg/day.
Tardive dyskinesia.
40 mg/day used in combination with neuroleptics.
?Intrathecal Initial screening bolus.
50 mcg/mL given into the intrathecal space by barbotage over a period of not less than 1 min. The client is observed for 4-8 hr for a positive response consisting of a decrease in muscle tone, frequency, and/or severity of muscle spasms. If the response is not adequate, a second bolus dose of 75 mcg/1.5 mL, 24 hr after the first bolus dose, can be given with the client observed for 4-8 hr. If the response is still inadequate, a final bolus screening dose of 100 mcg/2 mL can be given 24 hr later.
Postimplant dose titration.
To determine the initial daily dose of baclofen following the implant for intrathecal use, the screening dose that gave a positive response should be doubled and given over a 24-hr period. However, if the effectiveness of the bolus dose lasted for more than 12 hr, the daily dose should be the same as the screening dose but delivered over a period of 24 hr. After the first 24 hr, the dose can be increased slowly by 10%-30% increments only once each 24 hr until the desired effect is reached.
Maintenance therapy.
The maintenance dose may need to be adjusted during the first few months of intrathecal therapy. The daily dose may be increased by 10% to no more than 40% daily. If side effects occur, the daily dose may be decreased by 10%-20%. Daily doses for long-term continuous infusion have ranged from 12 to 1,500 mcg (usual maintenance is 300-800 mcg/day). The lowest dose producing optimal control should be used.
Reduce spasticity of cerebral palsy in children.
25, 50, or 100 mcg.