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Wednesday, July 23, 2025

Baclofen


Baclofen is a centrally acting skeletal muscle relaxant primarily used to treat spasticity associated with neurological disorders such as multiple sclerosis, spinal cord injury, cerebral palsy, and occasionally stroke. It is also prescribed off-label for certain types of neuropathic pain, intractable hiccups, and alcohol use disorder. Baclofen is available in both oral and intrathecal formulations, allowing for systemic and targeted delivery to the central nervous system (CNS).

Brand Names

Baclofen is marketed globally under various brand and generic names. Common brand names include:

  • Lioresal®

  • Gablofen® (intrathecal injection, U.S.)

  • Kemstro®

  • Ozobax® (oral solution)

  • Baclon®, Bacloheal®, Baclosign®, and others (generic formulations)

Available forms include:

  • Tablets: 10 mg, 20 mg

  • Oral solution: 5 mg/5 mL (e.g., Ozobax)

  • Intrathecal injection: for use via implantable pumps (e.g., Lioresal Intrathecal)

Mechanism of Action

Baclofen is a GABA<sub>B</sub> receptor agonist, which acts primarily at the spinal cord level to inhibit excitatory neurotransmission. It produces its effects through:

  • Binding to presynaptic GABA<sub>B</sub> receptors, leading to inhibition of voltage-gated calcium channels

  • Decreasing release of excitatory neurotransmitters like glutamate and substance P

  • Binding to postsynaptic GABA<sub>B</sub> receptors, causing potassium efflux and hyperpolarization

  • Ultimately, reducing the monosynaptic and polysynaptic reflexes involved in muscle tone, spasticity, and pain perception

Unlike benzodiazepines or GABA<sub>A</sub> modulators, baclofen does not act directly on GABA<sub>A</sub> receptors and thus lacks strong sedative or anxiolytic effects at therapeutic doses.

Therapeutic Uses

Approved Indications

  • Spasticity due to:

    • Multiple sclerosis

    • Spinal cord lesions or trauma

    • Cerebral palsy (oral or intrathecal, in severe cases)

    • Brain injury-related spasticity

    • Stroke (off-label; cautious use)

Off-label Uses

  • Alcohol use disorder (AUD): Reduces cravings and consumption; used in Europe more than the U.S.

  • Neuropathic pain: In selected cases such as trigeminal neuralgia, central pain syndrome

  • Persistent hiccups: Refractory to non-pharmacological treatment

  • Tourette syndrome

  • GERD with non-cardiac chest pain (by reducing transient lower esophageal sphincter relaxation)

  • Dystonia and spinal myoclonus

Dosage and Administration

Oral Baclofen (Adults)

  • Initial dose: 5 mg three times daily

  • Titrate gradually every 3–4 days:

    • 10 mg TID → 15 mg TID → 20 mg TID

  • Maximum dose: 80 mg/day (rarely up to 100 mg under specialist care)

Oral Baclofen (Children ≥2 years)

  • Based on body weight

  • Initial: 0.3 mg/kg/day divided in 3 doses

  • Maintenance: 0.75–2 mg/kg/day

Intrathecal Baclofen (ITB)

  • Reserved for severe spasticity unresponsive to oral therapy

  • Administered via implanted pump directly into cerebrospinal fluid

  • Initial test dose: 25–50 mcg bolus

  • Maintenance: 50–1200 mcg/day (depending on patient response)

  • Titrated carefully due to risk of CNS depression

Contraindications

  • Hypersensitivity to baclofen or formulation components

  • Active peptic ulcer disease (relative)

  • Epilepsy (use with caution; may lower seizure threshold)

  • Parkinson's disease (can worsen rigidity and akinesia)

  • Psychiatric disorders: History of psychosis or schizophrenia (increased risk of psychiatric side effects)

Precautions

  • Tapering: Baclofen must never be stopped abruptly, especially intrathecal form—may cause withdrawal symptoms, including seizures, hallucinations, and hyperthermia

  • Renal impairment: Reduce dose; baclofen is primarily renally excreted

  • Hepatic impairment: Caution advised; though not extensively metabolized, CNS toxicity may be exaggerated

  • CNS depressants: Additive sedation with opioids, benzodiazepines, antihistamines

  • Diabetes mellitus: May affect glycemic control; monitor blood sugar

Side Effects

Common (dose-dependent, usually transient)

  • Drowsiness

  • Dizziness or lightheadedness

  • Weakness or fatigue

  • Nausea

  • Constipation

  • Headache

  • Insomnia

  • Dry mouth

  • Hypotension

Neurological Effects

  • Confusion

  • Impaired coordination

  • Tremor

  • Depression

  • Visual disturbances

Psychiatric Effects (less common)

  • Hallucinations

  • Delirium

  • Suicidal ideation (rare; monitor closely in psychiatric patients)

Serious Adverse Events

  • Seizures (especially with abrupt withdrawal)

  • Respiratory depression (especially in ITB or high-dose use)

  • Coma

  • Bradycardia

  • Hypothermia

Withdrawal Symptoms

Abrupt discontinuation of oral or intrathecal baclofen may lead to:

  • Rebound spasticity

  • Hyperthermia

  • Rhabdomyolysis

  • Hallucinations

  • Agitation

  • Seizures

  • Delirium

  • Death (especially with ITB pump malfunction)

Gradual tapering is essential over 1–2 weeks when discontinuing therapy.

Drug Interactions

Pharmacodynamic Interactions

  • CNS depressants (e.g., opioids, benzodiazepines, alcohol): Increased risk of sedation, respiratory depression, and CNS toxicity

  • Antihypertensives: Additive hypotensive effect

  • Tricyclic antidepressants: May potentiate muscle relaxant effects

  • MAO inhibitors: Use cautiously; theoretical risk of hypertensive crisis or CNS effects

Pharmacokinetic Interactions

  • Baclofen is not significantly metabolized via cytochrome P450; major pharmacokinetic interactions are rare

  • NSAIDs and nephrotoxic agents: Monitor renal function when co-administered

Use in Special Populations

Pregnancy

  • Category C (US)

  • Crosses placenta; no clear evidence of teratogenicity, but use only if benefits outweigh risks

  • Neonatal withdrawal possible if used late in pregnancy

Lactation

  • Excreted into breast milk in low amounts

  • May be used with caution during breastfeeding; monitor infant for sedation

Pediatrics

  • Safe in children >2 years for spasticity

  • Intrathecal use restricted to specialized centers

Elderly

  • More sensitive to sedation, falls, and neurocognitive effects

  • Start at lower doses; titrate slowly

Comparison with Other Muscle Relaxants

Baclofen differs from:

  • Tizanidine: Acts on α<sub>2</sub> adrenergic receptors; more sedating and hypotensive

  • Diazepam: Acts on GABA<sub>A</sub>; more anxiolytic, higher abuse potential

  • Cyclobenzaprine: Similar to tricyclics; less effective for spasticity, more for acute muscle spasm

  • Dantrolene: Acts peripherally on skeletal muscle calcium release; used in malignant hyperthermia

Baclofen is preferred for chronic spasticity of CNS origin, especially in MS and SCI.

Patient Counseling Points

  • Take with or after food to minimize stomach upset

  • Do not stop abruptly; taper slowly under medical supervision

  • Avoid alcohol and sedatives unless advised

  • Report signs of:

    • Severe drowsiness or confusion

    • Muscle weakness or falls

    • Mood changes or hallucinations

    • Breathing difficulty (especially with ITB)

  • For intrathecal pump users:

    • Understand signs of pump malfunction

    • Adhere to refill schedule

    • Seek emergency care for sudden worsening of spasticity or withdrawal symptoms

Storage and Handling

  • Oral tablets: Store at room temperature, protect from moisture

  • Intrathecal solution: Store refrigerated (2–8°C); avoid light and discard unused portions

Regulatory Status

  • Prescription-only

  • Available worldwide in oral form

  • Intrathecal formulation restricted to specialist use only




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