Baclofen

Pronunciation: (BACK-low-fen)Class: Skeletal muscle relaxant, Centrally acting

Trade Names:Lioresal- Tablets 10 mg- Tablets 20 mg- Intrathecal 0.05 mg/mL (50 mcg/mL)- Intrathecal 10 mg/20 mL (500 mcg/mL)- Intrathecal 10 mg/5 mL (2000 mcg/mL)

APO-Baclofen (Canada)Gen-Baclofen (Canada)PMS-Baclofen (Canada)ratio-Baclofen (Canada)

Pharmacology

May inhibit transmission of reflexes at spinal level, possibly by action (hyperpolarization) at primary afferent fiber terminals, resulting in relief of muscle spasticity; has CNS depressant properties.

Pharmacokinetics

Absorption

Rapidly and extensively absorbed.

Elimination

Primarily by the kidney in unchanged form.

Indications and Usage

Oral

Treatment of reversible spasticity resulting from multiple sclerosis. May be of some value in patients with spinal cord injuries and other spinal cord diseases.

Intrathecal

Treatment of severe spasticity of spinal cord origin in patients who are unresponsive to or cannot tolerate oral baclofen therapy. Used intrathecally in single bolus test doses; chronic use requires implantable pump.

Unlabeled Uses

Oral

Therapy for trigeminal neuralgia (tic douloureux); tardive dyskinesia.

Intrathecal

Cerebral palsy spasticity in children.

Contraindications

Treatment of spasms from rheumatic disorders, stroke, cerebral palsy and Parkinson disease; use of intrathecal form via IV, IM, subcutaneous, or epidural routes.

Dosage and Administration

Adults Initial dose

PO 5 mg 3 times daily; may be increased by 5 mg/dose every 3 days as needed to max 80 mg/day (20 mg 4 times daily). Intrathecal Refer to manufacturer's manual for implantable pump.

ScreeningAdults

1 mL of 50 mcg/mL dilution is administered into the intrathecal space by barbotage over 1 min and patient is observed for 4 to 8 h; may be repeated 24 h later with 75 mcg/1.5 mL and 48 h later with 100 mcg/2 mL. Do not give implantable pump to patients not responding to 100 mcg bolus.

Children

The starting screening dose for children is the same as in adult patients (eg, 50 mcg). However, for very small patients, a screening dose of 25 mcg may be tried first.

Postimplant Dose Titration Period

To determine the initial total daily dose of baclofen following implant, double the screening dose that gave a positive effect and administer over a 24-h period.

Spasticity of Spinal Cord OriginAdults

Intrathecal After the first 24 h, increase the daily dosage slowly in 10% to 30% increments and only once every 24 h, until desired effect is achieved.

Spasticity of Cerebral OriginAdults

Intrathecal After the first 24 h, increase the daily dose slowly 5% to 15% once every 24 h, until desired clinical effect is achieved.

Children

After the first 24 h, increase the daily dose slowly 5% to 15% only once every 24 h, until the desired effect is achieved.

Maintenance Therapy for Spasticity of Spinal Cord Origins

Very often the maintenance dose needs to be adjusted during the first few months of therapy while patients adjust to changes in life-style because of the alleviation of spasticity.

Adults

Intrathecal During periodic refills of the pump, the daily dose may be increased 10% to 40%, but no more than 40%, to maintain adequate symptom control. Maintenance dose for long-term continuous infusion has ranged from 12 to 2,003 mcg/day, with most patients adequately maintained on 300 to 800 mcg/day.

Maintenance Therapy for Spasticity of Cerebral Origin

Very often the maintenance dose needs to be adjusted during the first few months of therapy while patients adjust to changes in life style because of the alleviation of spasticity.

Adults

Intrathecal During the periodic refills of the pump, the daily dose may be increased 5% to 20%, but no more than 20%. Ranges from 22 to 1,400 mcg/day, with most patients adequately maintained on 90 to 703 mcg/day.

Children less than 12 yr of age

Average daily dose 274 mcg/day. Requires individual titration. Use the lowest dose with an optimal response.

Children at least 12 yr of age

Same as adult. Determination of the optimal dose requires individual titration. Use the lowest dose with an optimal response.

General Advice

• Administer with milk or food to avoid GI upset.
• Dilute intrathecal medication per manufacturer's instructions.

Storage/Stability

Oral

Do not store above 86°F.

Intrathecal

Do not store above 86°F. Do not freeze. Do not heat sterilize.

Drug Interactions

CNS depressants

May cause increased sedative effects.

Morphine (epidural)

May cause hypotension and dyspnea.

Laboratory Test Interactions

May cause false elevation of AST, alkaline phosphatase, or blood glucose.

Adverse Reactions

Cardiovascular

Hypotension; palpitations; chest pain.

CNS

Drowsiness; weakness in lower extremities; dizziness; seizures; headache; numbness; euphoria; depression; confusion; lethargy; insomnia; hallucinations; paresthesia; asthenia; anxiety; agitation.

Dermatologic

Pruritus; rash.

EENT

Tinnitus; blurred vision; taste disorder; nasal congestion.

GI

Nausea; vomiting; dry mouth; constipation; diarrhea; abdominal pain; anorexia.

Genitourinary

Urinary frequency; enuresis; dysuria; impotence.

Respiratory

Dyspnea; pneumonia; hypoventilation.

Miscellaneous

Hypotonia; slurred speech; muscle pain; ankle edema; excessive perspiration; weight gain; back pain.

Precautions

Warnings Intrathecal Abrupt discontinuation has resulted in high fever, altered mental status, exaggerated rebound spasticity, and muscle rigidity that in rare cases advances to rhabdomyolysis, multiple organ system failure and death. Give special attention to patients at apparent risk (eg, spinal cord injuries at T-6 or above, communication difficulties, history of withdrawal symptoms from oral or intrathecal baclofen).

Pregnancy

Category C .

Lactation

Excreted in breast milk.

Children

Safety of oral baclofen in children younger than 12 yr of age and of intrathecal baclofen in children younger than 4 yr of age has not been established.

Renal Function

Administer with caution. Dosage reduction may be necessary.

Intrathecal use

Only specially trained personnel should administer baclofen intrathecally because of potentially life-threatening CNS depression, CV collapse, or respiratory failure.

Epilepsy and psychotic disorders

Use with caution because of potential exacerbations.

Fatalities

Fatalities occurred in premarketing trials of intrathecal baclofen; baclofen's role in these deaths is unknown.

Infection

Patients should be infection-free before screening trial with baclofen intrathecal.

Stroke

Baclofen has not significantly benefited patients with stroke; these patients also have poor drug tolerance.

Overdosage

Symptoms

Vomiting, muscular hypotonia, muscle twitching, drowsiness, accommodation disorders, coma, respiratory depression, seizures (oral); drowsiness, lightheadedness, dizziness, somnolence, respiratory depression, seizures (intrathecal).

Patient Information

• Instruct patient to take drug exactly as prescribed. If dose is missed it should be taken within 1 h. Warn patient not to double up on doses.
• Explain that full effectiveness of drug may not occur until several weeks after initiation of drug therapy.
• Warn patient not to discontinue medication abruptly. Explain that hallucinations or seizures may occur.
• Instruct patient to avoid intake of alcoholic beverages or other CNS depressants.
• Teach patient to avoid sudden position changes to prevent orthostatic hypotension.
• Caution diabetic patient that false elevation of blood glucose may occur. Instruct patient to monitor blood glucose carefully.
• Instruct patient to report the following symptoms to health care provider: dizziness, nausea, hypotension, urinary frequency, retention, painful urination, headache, seizures, weakness.
• Advise patient that drug may cause drowsiness, and to use caution while driving or performing other tasks requiring mental alertness.

Copyright © 2009 Wolters Kluwer Health.