Baclofen
Class: GABA derivative musculoskeletal muscle relaxant
Indications: relief of musculoskeletal spasm & associated pain; Intractable hiccup in palliative care
Contraindications/cautions: epilepsy, psychosis, schizophrenia, depression, mania, peptic ulceration (oral use), cerebrovascular disease, alcoholism, diabetes (may increase blood glucose concentrations), hypertension; hypertonic bladder sphincter; porphyria
Adverse reactions: common: nausea, sedation (caution driving), somnolence; less common: decreased cardiac output, hypotension, GI disturbance (constipation, nausea, vomiting), respiratory depression, light-headedness, personality changes, headache, insomnia, euphoria, depression, weakness, tremor, hallucinations, dry mouth, tinnitus, anxiety, agitation, urinary disturbances; visual disorders; rash, hyperhidrosis
Metabolism/clearance: mainly excreted in urine unchanged (80%) so dose adjust in renal impairment or increase dose interval. Use with caution if eGFR < 15 mL/min/1.73m2
Interactions:
- additive drowsiness and CNS depression with other CNS depressant drugs e.g. alcohol, benzodiazepines (e.g. clonazepam), opioids
- increased muscle relaxation with tricyclic antidepressants e.g. nortriptyline, amitriptyline
| Dosing: | |
|---|---|
| Oral: | 5 to 20 mg 3 times a day (start at 5 mg 3 times a day); increase slowly every 3 days up to 10 to 20 mg 3 times daily. Assess risk/benefit |
| Subcut: | not available |
| Intrathecal use: | seek specialist advice |
Syringe driver: only intrathecal inj available – not for subcut use Mechanism of action: works in the spinal cord where it stimulates GABA-receptors which inhibit the release of glutamate and aspartate (excitatory). Also has CNS depressant actions
Onset: variable – hours to weeks
Notes: • stopping abruptly may result in a withdrawal reaction (confusion, psychosis, tachycardia, hyperthermia and rebound spasticity). Gradual dose reduction recommended over 1 to 2 weeks
Availability:
- tablets 10 mg
- intrathecal 50 micrograms/mL; 10 mg/5 mL; 10 mg/20 mL
- extemporaneously compounded liquid may be available from pharmacy (1 mg/mL)