Adult: Spasticity of spinal or cerebral origin (associated with injury, multiple sclerosis, cerebral palsy) in patients who are unresponsive to oral baclofen or other oral antispastic agents, and/or those who experience unacceptable side effects at effective oral doses: Screening: Initially, 25 mcg or 50 mcg via spinal catheter or lumbar puncture over at least 1 minute, increase the dose by 25 mcg increments at intervals of at least 24 hours until response of approx 4-8 hours duration is obtained. Non-responders to a 100 mcg test dose are not suitable for intrathecal treatment. Dose-titration: The initial total daily dose via infusion is determined by doubling the test dose which gave a significant response administered over 24 hours. For patients with response lasting more than 12 hours, the unchanged test dose may be given over 24 hours without any dose increase. After the 1st 24 hours, slowly adjust dosage in increments of 10-30% of the previous daily dose for spasticity of spinal origin, or 5-15% of the previous daily dose for spasticity of cerebral origin once every 24 hours for programmable pumps, or every 48 hours for non-programmable multi-dose reservoir pumps, until the desired clinical effect is achieved. Maintenance dose range: 12-2,003 mcg daily for spasticity of spinal origin; 22-1,400 mcg daily for spasticity of cerebral origin. Child: Spasticity of cerebral or spinal origin (associated with injury, multiple sclerosis, or other spinal cord diseases) in patients who are unresponsive to oral baclofen or other oral antispastic agents, and/or those who experience unacceptable side effects at effective oral doses: 4 to <18 years Screening: Initially, 25-50 mcg daily via lumbar puncture over at least 1 minute according to the patient’s age and size. Non-responders may receive 25 mcg daily dose escalation every 24 hours. Max test dose: 100 mcg daily. Maintenance dose range: 25-200 mcg daily (median dose: 100 mcg daily), adjusted according to individual response.
Oral Severe chronic spasticity
Adult: Spasticity resulting from multiple sclerosis, tumours of the spinal cord, syringomyelia, motor neurone disease, transverse myelitis, traumatic partial section of the cord, cerebrovascular accidents, cerebral palsy, meningitis, or traumatic head injury: Initially, 15 mg daily preferably in divided doses, may be increased gradually according to individual requirements. Suggested regimen: 5 mg tid for 3 days, increased to 10 mg tid for 3 days, then increased to 15 mg tid for 3 days, until increased to 20 mg tid for 3 days but adjusted carefully according to individual requirements. Re-assess treatment if therapeutic effect is not apparent within 6 weeks of achieving max dosage. Elderly: Use lower initial dose, titrated gradually according to individual response. Child: Spasticity of cerebral origin especially infantile cerebral palsy, following cerebrovascular accidents, or presence of neoplastic or degenerative brain disease; spinal cord diseases of infectious, degenerative, traumatic, neoplastic or unknown origin such as multiple sclerosis, spastic spinal paralysis, amyotrophic lateral sclerosis, syringomyelia, transverse myelitis, traumatic paraplegia or paraparesis, compression of the spinal cord: 0 to <18 years >33 kg: Initially, 0.3 mg/kg daily preferably in 4 divided doses, may be increased gradually at approx 1 week intervals until dosage becomes sufficient according to individual requirements. Maintenance dose range: 0.75-2 mg/kg daily. Max: <8 years 40 mg daily; >8 years 60 mg daily.
Renal Impairment
Oral:
Renally impaired or undergoing chronic haemodialysis: Reduce dose to approx 5 mg daily. Intrathecal:
Dose reduction may be required.
Administration
Should be taken with food.
Reconstitution
Oral solution: May be diluted with purified water BP if necessary. Intrathecal: May be diluted under aseptic conditions with sterile preservative-free NaCl for inj.
Incompatibility
Intrathecal: Incompatible with other solutions for inj or infusion e.g. dextrose.
Contraindications
Oral: Peptic ulceration. Intrathecal: Not intended for IV, IM, SC or epidural administration.
Special Precautions
Patients with psychotic disorders, schizophrenia, depressive or manic disorders, confusional states, Parkinson’s disease, epilepsy or history of seizure disorders, cerebrovascular or respiratory insufficiency, history of peptic ulcers, decreased gastrointestinal motility and/or obstructive disorders, pre-existing sphincter hypertonia, diabetes mellitus, history of autonomic dysreflexia (intrathecal), spasticity of cerebral origin, or spasticity needed to sustain upright posture and balance in locomotion. Not indicated for treatment of spasticity associated with rheumatic disorders. Avoid abrupt withdrawal. Renal impairment including ESRD. Children and elderly. Pregnancy and lactation.
Adverse Reactions
Significant: Respiratory depression, intrathecal mass formation, acute urinary retention, CNS depression; oral: drug withdrawal syndrome (e.g. hyperactive state with rapid uncontrolled spasms, hyperthermia, autonomic dysreflexia, infection or sepsis, malignant hyperthermia). Rarely, elevated AST and serum alkaline phosphatase, increased blood glucose levels. Cardiac disorders: Bradycardia. Eye disorders: Accommodation disorder, blurred vision, nystagmus, diplopia. Gastrointestinal disorders: Nausea, vomiting, dry mouth, constipation, diarrhoea, increased salivation. General disorders and administration site conditions: Fatigue, ataxia, lethargy, asthenia, pyrexia, pain, chills, facial or peripheral oedema. Investigations: Cardiac output decreased. Metabolism and nutrition disorders: Dehydration, decreased appetite. Musculoskeletal and connective tissue disorders: Muscle weakness, myalgia, hypotonia. Nervous system disorders: Sedation, somnolence, dizziness, headache, tremor, paraesthesia, memory impairment. Psychiatric disorders: Confusional state, insomnia, hallucination, depression, anxiety, agitation, euphoric mood, dysarthria, nightmares. Renal and urinary disorders: Pollakiuria, enuresis, dysuria, urinary incontinence. Reproductive system and breast disorders: Sexual dysfunction (intrathecal). Respiratory, thoracic and mediastinal disorders: Dyspnoea, pneumonia. Skin and subcutaneous tissue disorders: Rash, hyperhidrosis, pruritus. Vascular disorders: Hypotension, flushing, pallor. Potentially Fatal: Intrathecal: Drug withdrawal syndrome (e.g. altered mental status, exaggerated rebound spasticity, muscle rigidity, rarely rhabdomyolysis, multiple organ-system failure, and death).
This drug may cause dizziness, sedation, somnolence or visual impairment, if affected, do not drive or operate machinery.
Monitoring Parameters
Monitor renal and liver function; EEG regularly in patients with epilepsy.
Overdosage
Symptoms: Oral: Signs of CNS depression such as somnolence, depressed level of consciousness, coma, respiratory depression; confusion, hallucination, agitation, convulsion, abnormal ECG, accommodation disorder, impaired pupillary reflex, generalised muscular hypotonia, myoclonus, hyporeflexia or areflexia, peripheral vasodilation, hypotension or hypertension, bradycardia, tachycardia or cardiac arrhythmia, hypothermia, nausea, vomiting, diarrhoea, salivary hypersecretion, increased hepatic enzymes, and rhabdomyolysis. Intrathecal: Dizziness, somnolence, drowsiness, light-headedness, excessive muscular hypotonia, seizures, loss of consciousness, hypothermia, nausea and vomiting, excessive salivation, respiratory depression, apnoea, and coma. Management: Symptomatic and supportive treatment. Oral: May administer generous amounts of fluids together with diuretics. May undergo haemodialysis in severe poisoning associated with renal failure. Intrathecal: Remove the remaining residual solution from the reservoir of the programmable continuous infusion pump. If it is possible without surgical intervention, disconnect the intrathecal catheter from the pump and allow the infusion fluid to drain back together with some CSF (up to 30-40 mL). May intubate and ventilate patients with respiratory depression if necessary. May administer IV diazepam with CV support in the event of convulsions.
Drug Interactions
Increased risk of adverse events (e.g. nausea, mental confusion, hallucination, agitation) of levodopa/carbidopa. Increased sedation and risk of respiratory depression with other muscle relaxants (e.g. tizanidine), synthetic opiates, CNS depressants, analgesics, neuroleptics, barbiturates, benzodiazepines, anxiolytics. Increased risk of hypotension and dyspnoea with morphine. May potentiate effects of TCAs resulting in pronounced muscular hypotonia. Increased risk of cardiac disturbances and seizures with general anaesthetics (e.g. fentanyl, propofol). May aggravate hyperkinetic symptoms with lithium. Increased risk of hypotension with antihypertensives. May increase risk of toxic effects with other drugs that significantly affect renal function.
Food Interaction
Enhanced CNS depressant effect with alcohol.
Action
Description: Mechanism of Action: Baclofen, a structural analogue of neurotransmitter GABA, is a centrally acting skeletal muscle relaxant. It inhibits the transmission of both monosynaptic and polysynaptic reflexes at the spinal cord level, possibly by stimulating the GABAB-receptors which inhibits the release of excitatory amino acids glutamate and aspartate, or by hyperpolarisation of the primary afferent fibre terminals resulting in muscle spasticity relief. Onset: Intrathecal bolus: 0.5-1 hour; Continuous infusion: 6-8 hours after infusion initiation. Pharmacokinetics: Absorption: Rapidly and almost completely absorbed from gastrointestinal tract. Bioavailability: Approx 74% (oral). Time to peak plasma concentration: Approx 1 hour (oral). Distribution: Crosses the blood-brain barrier, with CSF concentrations approx 8.5 times lower than in plasma. Crosses placenta and enters breast milk. Volume of distribution: 0.7 L/kg (oral); 22-157 mL (intrathecal). Plasma protein binding: Approx 30%. Metabolism: Metabolised in the liver via deamination to form its main inactive metabolite, β-(p-chlorophenyl)-4-hydroxybutyric acid. Excretion: Mainly via urine (>70% as unchanged drug); faeces. Elimination half-life: Plasma: Approx 3.75±0.96 hours (oral); CSF: Approx 1.51 hours over the 1st 4 hours (intrathecal).
Chemical Structure
Baclofen Source: National Center for Biotechnology Information. PubChem Database. Baclofen, CID=2284, https://pubchem.ncbi.nlm.nih.gov/compound/Baclofen (accessed on Jan. 21, 2020)
Storage
Tab: Store between 20-25°C. Protect from heat and moisture. Oral solution: Store below 25°C. Protect from light. Do not refrigerate. Intrathecal inj: Store below 30°C. Do not refrigerate, freeze or heat sterilise.
M03BX01 - baclofen ; Belongs to the class of other centrally-acting muscle relaxants.
References
Anon. Baclofen . AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 19/08/2019.Anon. Baclofen. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 19/08/2019.Baclofen 5mg/5 mL Oral Solution (Strides Pharma UK Ltd). MHRA. https://products.mhra.gov.uk/. Accessed 19/08/2019.Buckingham R (ed). Baclofen . Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 19/08/2019.Gablofen (Mallinckrodt Inc, Brand Pharmaceuticals). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 19/08/2019.
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