BACLOFEN

BACLOFEN
(bak'loe-fen)
Kemstro, Lioresal
Classifications: central-acting skeletal muscle relaxant; gaba agonist;
Therapeutic: skeletal muscle relaxant

Prototype: Cyclobenzaprine
Pregnancy Category: C

Availability

10 mg, 20 mg tablets; 10 mg, 20 mg orally disintegrating tablets; 50 mcg/mL, 250 mcg/mL ampules

Action

Centrally acting skeletal muscle relaxant. Depresses monosynaptic and polysynaptic afferent reflex activity at spinal cord level. Baclofen stimulates the GABA receptors, which results in decreased excitatory input into alpha-motor neurons.

Therapeutic Effect

Reduces skeletal muscle spasm caused by upper motor neuron lesions.

Uses

Symptomatic relief of painful spasms in multiple sclerosis and in the management of detrusor sphincter dyssynergia in spinal cord injury or disease.

Unlabeled Uses

Treatment of trigeminal neuralgia and of tardive dystonia associated with antipsychotic medications, chronic pain.

Contraindications

Pregnancy (category C), coagulopathy, bacteremia, intramuscular or intrathecal administration, subcutaneous administration.

Cautious Use

Impaired renal and hepatic function; bipolar disorder, psychosis, schizophrenia, seizure disorders, seizures, stroke, cerebral palsy, depression, diabetes mellitus, dialysis, head trauma, PKU, epilepsy; thrombocytopenia; psychiatric or brain disorders; older adults, children <2 y.

Route & Dosage

Muscle Spasm
Adult: PO 5 mg t.i.d., may increase by 5 mg/dose q3d prn (max: 80 mg/d)
Child: PO 2–7 y, 10–15 mg/d divided q8h, may increase by 5–15 mg/d q3d (max: 40 mg/d); ≥8 y, 10–15 mg/d divided q8h, may increase by 5–15 mg/d q3d (max: 60 mg/d)
Adult: Intrathecal Prior to infusion pump implantation, initiate trial dose of 50 mcg/mL bolus administered in intrathecal space by barbotage over ≤1 min. Observe patient over next 4–8 h for significant decrease in muscle spasm. If response is less than desired, administer second bolus of 75 mcg/1.5 mL and observe 4–8 h. May repeat in 24 h with a 100 mcg/2-mL bolus if necessary. Post-implant titration: Use screening dose if response lasted >12 h or double screening dose if response lasted <12 h and administer over 24 h. After first 24 h, decrease dose by 10–30% q24h until desired response achieved. Maintenance doses range from 12–1500 mcg/d, with most patients maintained on 300–800 mcg/d.

Administration

Oral
  • Give with food or milk to avoid GI distress.
Intrathecal
  • Give by direct intrathecal injection (via lumbar puncture or catheter) over at least 1 min or longer.
  • Dilute only with sterile, preservative free NS injection. Baclofen must be diluted to a concentration of 50 mcg/mL when preparing test doses.
  • Intrathecal infusion pump: Do not abruptly discontinue as serious adverse effects may develop.
  • Store at 15°–30° C (59°–86° F) in tightly closed container unless otherwise directed.

Adverse Effects (≥1%)

CNS: Transient drowsiness, vertigo, dizziness, weakness, fatigue, headache, confusion, insomnia; ataxia, loss of seizure control in epileptic patients; abrupt discontinuation of intrathecal administration may result in high fever, altered mental status, exaggerated rebound spasticity, and muscle rigidity, that in rare cases has advanced to rhabdomyolysis, multiple organ-system failure, and death. CV: Hypotension. Special Senses: Tinnitus, nasal congestion; blurred vision, mydriasis, nystagmus, diplopia, strabismus, miosis. GI: Nausea, constipation, vomiting; mild increases in AST, and alkaline phosphatase, jaundice. Urogenital: Urinary frequency.

Diagnostic Test Interference

Possibility of increases in blood-glucose, serum alkaline phosphatase, and AST levels.

Interactions

Drug: Alcohol, cns depressants, mao inhibitors, antihistamines compound CNS depression; baclofen may increase blood glucose levels, making it necessary to increase dosage of sulfonylureas, insulin.

Pharmacokinetics

Absorption: Readily from GI tract. Peak: 2–3 h. Duration: 8 h. Distribution: Minimal amounts cross blood-brain barrier; crosses placenta; distribution into breast milk unknown. Metabolism: 15% in liver. Elimination: 70–85% in urine within 72 h; some elimination in feces. Half-Life: 3–4 h.

Nursing Implications

Assessment & Drug Effects

  • Supervise ambulation. Initially, the loss of spasticity induced by baclofen may affect patient's ability to stand or walk.
  • Lab tests: Baseline and periodic BP, weight, blood sugar, hepatic function tests, and urine.
  • Monitor for adverse neuropsychiatric or genitourinary symptoms that resemble those of the underlying disease. Assess them carefully and report to the physician.
  • Observe carefully for side effects: mental confusion, depression, hallucinations. Older adults are especially sensitive to this drug.
  • Monitor patients with epilepsy closely for possible loss of seizure control.

Patient & Family Education

  • Note: CNS depressant effects will be additive to other CNS depressants, including alcohol.
  • Monitor blood glucose for loss of glycemic control if diabetic.
  • Do not drive or engage in other potentially hazardous activities until the response to drug is known.
  • Report adverse reactions to physician. Most can be reduced by decreasing dosage. Incidence of CNS symptoms (drowsiness, dizziness, ataxia) are reportedly high in patients >40 y of age.
  • Do not self-dose with OTC drugs without physician's approval.
  • Do not stop this drug unless directed to do so by physician. Drug withdrawal needs to be accomplished gradually over a period of 2 wk or more. Abrupt withdrawal following prolonged administration may cause anxiety, agitated behavior, auditory and visual hallucinations, severe tachycardia, acute exacerbation of spasticity, and seizures.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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