Baclofen

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.
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.
Elderly: Use lower initial dose, titrated gradually according to individual response.
Renal impairment: Renally impaired or undergoing chronic haemodialysis: Reduce dose to approx 5 mg daily.
Reconstitution: Oral solution: May be diluted with purified water BP if necessary.

Intrathecal
Severe chronic spasticity
Adult: In patients unresponsive to oral therapy and/or with unacceptable side effects at effective doses: Screening: Initially, 25 mcg or 50 mcg via spinal catheter/lumbar puncture over ≥1 minute, increase dose by 25 mcg increments at 24-hr intervals until response of approx 4-8 hrs duration. Treatment is not suitable for non-responders to 100 mcg test dose. Titration: Determine initial total daily dose via infusion by doubling test dose that has significant response administered over 24 hrs. For patients with response >12 hrs, give the unchanged test dose over 24 hrs without dose increase. After 24 hrs, slowly adjust dose in increments of 10-30% (spasticity of spinal origin) or 5-15% (spasticity of cerebral origin) of the previous daily dose 24 hourly for programmable pumps or 48 hourly for non-programmable multi-dose reservoir pumps until the desired effect is achieved. Maintenance: 12-2,003 mcg daily (spasticity of spinal origin); 22-1,400 mcg daily (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.
Renal impairment: Dose reduction may be required.
Reconstitution: 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.

Should be taken with food.

Oral: Peptic ulceration. Intrathecal: Not intended for IV, IM, SC or epidural administration.

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. Patient Counselling 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.

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).

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.

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.

Enhanced CNS depressant effect with alcohol.

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 GABA_B-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.
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).

Intrathecal: Intrathecal inj: Store below 30°C. Do not refrigerate, freeze or heat sterilise. Oral: Tab: Store between 20-25°C. Protect from heat and moisture. Oral solution: Store below 25°C. Protect from light. Do not refrigerate.

Muscle Relaxants

M03BX01 - baclofen ; Belongs to the class of other centrally-acting muscle relaxants.