·
Baclofen is used to treat muscle
spasticity, clonus, flexor spasms, spinal disorders and multiple sclerosis.
·
Baclofen is a derivative of the
inhibitory neurotransmitter GABA (gamma
amino butyric acid).
·
It inhibits both monosynaptic and
polysynaptic reflexes at spinal level and also has CNS depressant effects.
·
Baclofen appears to act as a
presynaptic GABA-B receptor agonist, and reduces the tonic activity of spinal
gamma-motor-neurons, probably by acting at a novel receptor site.
·
At therapeutic doses (40 to 80
mg/day), baclofen is rela-tively free of adverse effects, and toxicity usually
manifests only at daily doses exceeding 150 to 200 mg/day.
·
Baclofen is well absorbed orally and
bioavailability is around 70 to 80%.
·
Peak plasma levels (usually 0.3 to
0.6 mg/ml)
are achieved in about 2 hours.
·
Plasma protein binding is to the
extent of 30%, while the apparent volume of distribution is 0.8 L/kg.
·
About 15% is metabolised by the
liver.
·
Approximately 85 to 90% of baclofen
is excreted unchanged in the urine, and about 10% in the faeces.
·
Elimination half-life ranges from 2
to 6 hours, though in overdose this may rise to more than 30 hours.
■■ Baclofen can potentiate the effects of other CNS depres-sants and
alcohol, as well as that of antihypertensives.
■■ Concomitant
administration of levodopa (in Parkinsonism) may sometimes cause confusion,
agitation, and hallucina-tions.
· Overdose is characterised by agitation,
involuntary move-ments, twitching, convulsions, delirium, flaccidity, coma, and
respiratory depression.
· Nausea and vomiting are common.
· There may also be hypo- or
hypertension, cardiac arrhyth-mias, and hypothermia.
o
Hypotension and bradycardia are the most common
cardiovascular complications.
o
Mild hypertension, tachycardia, first and second degree AV
block, QTc prolongation, atrial fibrillation, and PVCs have also been reported.
· Pupils are often dilated with
sluggish or no reaction to light. Less commonly, pupils may be normal or
miotic.
· Symptoms can occur very suddenly in
intrathecal injection overdose of baclofen, which may in fact present as coma.
Other effects include bradycardia, hypothermia, itching, dysphoria, drowsiness,
light-headedness, dizziness, somno-lence, respiratory depression, seizures, and
hypotonia.
· Baclofen has been associated with
encephalopathy. EEG changes in baclofen-induced encephalopathy include periodic
sharp waves, bursts of triphasic waves, trains of delta activity, intermittent
rhythmical delta waves, burst suppression pattern without reactivity to
stimulation, and diffuse background slowing.
· Long-term administration of
therapeutic doses of baclofen may cause fatigue, vertigo, nausea, confusion,
depression, headache, and muscle weakness. Movement disorders and memory
impairment have been described at therapeutic doses. Dystonia, chorea, akinetic
mutism, dyskinesia, and flapping tremor have also been reported at therapeutic
doses. Depression, confusion, mania, psychosis, amnesia, catatonia and mood
disorders can also occur. Abrupt with-drawal results in convulsions,
hallucinations, insomnia, confusion, and agitation. Withdrawal after chronic
intrathecal infusion may be more severe including severe rebound spasticity,
hyperthermia, hypotension, tachycardia, conduction disturbances (including
atrial fibrillation), rhabdomyolysis, disseminated intravascular coagulation,
hepatic injury, neuropsychiatric changes (i.e. mental status depression) and in
some cases multiorgan failure and death.
·
Blood baclofen levels of over 1.5 to
2 mcg/ml are indica- tive of toxicity.
·
Ingestion of 300 mg has caused
serious intoxication in healthy adults; elderly patients may develop CNS and
respiratory depression after 50 mg.
·
Admission to an intensive care facility, with gastric lavage
and activated charcoal, has been recommended for adults kg of baclofen.
·
Treatment of overdose involves oxygen administration,
assisted ventilation, gastric lavage (if patient is conscious and seen within 2
to 3 hours of ingestion), activated charcoal, IV diazepam for convulsions and
trendelen- berg position, IV fluids and pressor amines (dopamine or
noradrenaline) for hypotension.
·
Atropine has been reported to be useful in treating brady-
cardia and hypotension associated with baclofen overdose.
·
Institute continuous cardiac monitoring and assess adequacy
of respirations using pulse oximetry and/or arterial blood gases.
·
Physostigmine is said to be effective in reversing
respiratory depression, arreflexia, and coma. The usual dose is 1 to 2 mg by
slow IV infusion, repeated cautiously if required, all the while watching out
for adverse effects. The use of physostigmine is contraindicated in the
presence of cardiac depression. Since the vast majority of patients respond
well to supportive care, physostigmine is not recommended except for severe
toxicity not responsive to supportive measures.
·
Forced diuresis may be helpful in enhancing the elimination
of baclofen. The method advocated is NaCl 0.45% in 5% dextrose-in-water, with
furosemide 1 mg/kg (maximum 40 mg), to obtain a urine flow of 3 to 6
ml/kg/hour.
·
Haemodialysis has shortened the duration of toxic effects of
baclofen in several patients with severely impaired renal function.
·
Withdrawal symptoms respond to
reinstitution of baclofen with subsequent gradual tapering of the dose if
indicated. Treatment of intrathecal baclofen withdrawal should include the
restoration of intrathecal baclofen (ITB) (i.e. refill pump, change battery,
etc.); after ITB dosing clinical improvement should be noted within 30 minutes
with maximal benefit in 4 to 6 hours. If intrathecal restoration is not
immediately possible, begin oral baclofen and/or oral or intravenous
benzodiazepines may prevent potential fatal sequelae. Oral baclofen is not
anticipated to relieve all the symptoms related to intrathecal baclofen
withdrawal.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2024 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.