GABA-B Receptor Agonist (Muscle Relaxant / Antispastic)
Pregnancy: Avoid — neonatal withdrawal symptoms reported; taper and discontinue before delivery if possible; if essential during pregnancy, discuss risks
Baclofen
Brand names: Lioresal
Adult dose
Dose: Start 5 mg three times daily; increase by 5 mg/dose every 3 days to effective dose; usual maintenance 30–75 mg/day in divided doses
Route: Oral
Frequency: Three times daily
Max: 100 mg/day (oral); intrathecal pump doses vary
Spasticity of spinal origin (MS, spinal cord injury, stroke); intrathecal baclofen pump for severe refractory spasticity; NEVER stop abruptly (withdrawal seizures/hyperthermia)
Paediatric dose
Dose: 0.3 mg/kg/day divided three times daily; increase slowly mg/day/kg
Route: Oral
Frequency: Three times daily
Max: 2 mg/kg/day (max 60 mg/day for <8 years; 100 mg/day ≥8 years)
Cerebral palsy spasticity; intrathecal baclofen pump for severe cases (specialist)
Dose adjustments
Renal
Reduce dose significantly in renal impairment — baclofen is renally cleared; dose by response with caution; haemodialysis: avoid or use very low doses
Hepatic
No significant dose adjustment required
Paediatric weight-based calculator
Cerebral palsy spasticity; intrathecal baclofen pump for severe cases (specialist)
Clinical pearls
- Abrupt withdrawal is life-threatening: baclofen withdrawal syndrome includes rebound spasticity, fever, altered consciousness, seizures, and autonomic instability — resembling neuroleptic malignant syndrome; always taper slowly over 1-2 weeks when stopping; intrathecal pump failure is a medical emergency
- Spasticity-function paradox: in patients who use spasticity to maintain posture or ambulation (common in spinal cord injury), reducing spasticity with baclofen may paradoxically worsen functional ability — assess walking and transfers before and after dose changes
- Intrathecal baclofen pump: delivers drug directly to CSF via implanted pump — achieves much higher spinal cord concentrations at 1/100th of oral dose; avoids sedation; dramatic spasticity reduction in cerebral palsy and spinal cord injury; requires specialist implantation and programming
- Alcohol dependence off-label use: high-dose baclofen (30-300 mg/day, unlicensed) for alcohol dependence is used in some European centres (ALPADIR trial) — GABA-B agonism reduces craving; not NICE-recommended; French ANSM approved but MHRA has not; nalmefene and naltrexone are licensed alternatives
- Renal excretion: baclofen is ~80% renally cleared unchanged — accumulates significantly in renal failure causing severe CNS/respiratory depression; even moderate renal impairment requires dose reduction; dialysis does not clear baclofen efficiently
Contraindications
- Peptic ulcer disease (relative)
- Epilepsy (lowers seizure threshold — use with caution)
Side effects
- Drowsiness/sedation (most common)
- Dizziness
- Weakness (may worsen function if spasticity is maintaining standing ability)
- Nausea
- Confusion in elderly
- Urinary incontinence
- Withdrawal syndrome (seizures, hyperthermia, hallucinations — NEVER stop abruptly)
Interactions
- CNS depressants (benzodiazepines, opioids, alcohol) — additive sedation; avoid combination or reduce doses
- Antihypertensives — additive hypotension
- Tricyclics — additive muscle relaxation and sedation
Monitoring
- Spasticity assessment (Ashworth scale at each visit)
- Functional mobility (gait, transfers)
- Sedation level (Epworth sleepiness scale)
- Renal function (dose adjustment guidance)
- Withdrawal symptoms if dose reduced
Reference: BNFc; BNF 90; BNFc; NICE CG186 (Spasticity); MHRA SPC Lioresal; ALPADIR trial (Reynaud et al. 2017 — alcohol dependence off-label); Cochrane Review — antispastics in MS. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.