Baclofen Injection

Generic name: Baclofen

Drug class: Muscle relaxant and antispastic

Dosage form: Intrathecal injection

Root of administration: Intrathecal (into the spinal fluid)

Dose: Initial test dose: 100 mcg administered intrathecally. Maintenance therapy: 300 mcg/day to 800 mcg/day for spasticity of spinal cord origin; 90 mcg/day to 700 mcg/day for spasticity of cerebral origin. Dosage should be individualized based on patient response.

Mechanism of action: Baclofen is a gamma-aminobutyric acid (GABA) ergic agonist that inhibits both monosynaptic and polysynaptic reflexes at the spinal level, possibly by decreasing excitatory neurotransmitter release from primary afferent terminals.

Drug usage cases:

• Management of severe spasticity of cerebral or spinal origin in adult and pediatric patients aged 4 years and above.
• Reserved for patients unresponsive to oral baclofen therapy or those who experience intolerable central nervous system side effects at effective doses.
• Patients should first respond to a screening dose of intrathecal baclofen prior to consideration for long-term infusion via an implantable pump.
• Spasticity due to traumatic brain injury: wait at least one year after injury before considering baclofen injection therapy.

Drug contraindications:

• Hypersensitivity to baclofen.
• Not for intravenous, intramuscular, subcutaneous, or epidural administration.

Side effects:

• Hypotonia (34.7%).
• Somnolence (18.7%).
• Headache (10.7%).
• Agitation.
• Constipation.
• Leukocytosis.
• Chills.
• Urinary retention.
• Hypoventilation.
• Hypertonia.
• Paresthesia.
• Increased salivation.
• Back pain.
• Pruritus.
• Diarrhea.
• Peripheral edema.
• Asthenia.
• Pain.
• Confusion.
• Speech disorder.
• Amblyopia.
• Accidental injury.
• Dry mouth.

Warnings:

• DO NOT DISCONTINUE ABRUPTLY: Abrupt discontinuation of intrathecal baclofen can result in high fever, altered mental status, exaggerated rebound spasticity, muscle rigidity, and, in rare cases, rhabdomyolysis, multiple organ-system failure, and death.
• Special attention should be given to patients at apparent risk (e.g., spinal cord injuries at T-6 or above, communication difficulties, history of withdrawal symptoms from oral or intrathecal baclofen).

Use during pregnancy or breastfeeding:

Pregnancy Category C: The effect of baclofen in labor and delivery is unknown. Baclofen is excreted into breast milk at oral therapeutic doses. Safety and effectiveness in pediatric patients below the age of 4 years have not been established.