- USES: Centrally acting muscle relaxant used in the treatment of muscle spasms secondary to conditions such as multiple sclerosis and spinal cord injuries. Occasionally used as a drug of abuse. PHARMACOLOGY: Derivative of gamma aminobutyric acid (GABA); acts at the spinal end of upper motor neurons, inhibits monosynaptic and polysynaptic reflexes at the spinal level. TOXICOLOGY: Presynaptic GABA-B agonist, in overdose causes CNS depressive effects similar to other GABA agonists. EPIDEMIOLOGY: Deliberate overdose is unusual. Inadvertent intrathecal overdose occurs rarely secondary to pump malfunctions or dispensing errors. Episodically used as a drug of abuse. MILD TO MODERATE TOXICITY: Lethargy, somnolence, confusion, agitation, hallucinations, delirium, nausea, and vomiting are fairly common. Mild elevations in liver enzymes, urinary retention, and incontinence are less common effects. SEVERE TOXICITY: Bradycardia, hypotension, coma, respiratory failure, seizures, mydriasis, flaccidity, and mild hypothermia may develop. Rare effects include status epilepticus, rhabdomyolysis, and first-degree AV block. Coma, flaccidity and loss of reflexes can last for several days after severe overdose and should not be mistaken for brain death. WITHDRAWAL: Abrupt discontinuation of baclofen (usually intrathecal), for any reason, can result in withdrawal symptoms, which have included hyperthermia, tachycardia, altered mental status (ie, hallucinations, delirium, agitation), exaggerated rebound spasticity, muscle rigidity, seizures, hypertension, and hypotension, and in rare cases manifestations may progress to rhabdomyolysis, multiple organ-system failure and death.
Range of Toxicity:
- TOXICITY: ADULT: Ingestions of greater than 200 mg usually produces significant toxicity in healthy adults, including seizures, coma, delirium and the need for mechanical ventilation. CNS and respiratory depression may occur after 50 mg in the elderly. Intrathecal doses of 1.5 mg and above have caused coma and respiratory failure. Fatalities are rare, but have been reported in adults with ingestions of a gram or more. INFANT: 120 mg has resulted in respiratory arrest. THERAPEUTIC DOSE: ADULT: The recommended oral dosage range is 40 to 80 mg daily in 3 to 4 divided doses. PEDIATRIC: Safety and efficacy have not been established in pediatric patients.
- Support: MANAGEMENT OF MILD TO MODERATE TOXICITY: Most baclofen exposures require only supportive care. Treat agitation or seizures with benzodiazepines. MANAGEMENT OF SEVERE TOXICITY: Treat seizures with benzodiazepines. Treat hypotension with fluids and pressors if needed. Manage airway in patients with CNS depression or recurrent seizures. Coma, flaccidity and absent reflexes can persist for more than 5 days after severe overdose and should not be mistaken for brain death.
- Decontamination: PREHOSPITAL: Activated charcoal is not recommended because of the risk of CNS depression and aspiration. HOSPITAL: Administer activated charcoal, in patients who are alert or in whom airway is protected, for adults ingesting more than 100 mg and children ingesting more than 5 mg/kg. Fatalities are rare, most patients do well with supportive care; gastric lavage is generally not warranted.
- Airway management: Monitor for CNS and/or respiratory depression and need for endotracheal intubation.
- Antidote: None
- Seizure: IV benzodiazepines and barbiturates.
- Hypotensive episode: IV 0.9 NaCl at 10 mL to 20 mL/kg, dopamine, norepinephrine.
- Bradycardia: Evaluate for hypoxia, administer oxygen and manage airway as necessary. If associated with hypotension, administer atropine.
- Intrathecal injection: After intrathecal overdose from an indwelling pump, remaining baclofen intrathecal solution should be emptied from the pump reservoir as soon as possible. If NOT contraindicated, withdraw 30 to 40 mL CSF by lumbar puncture or through the catheter access port to reduce baclofen concentration in the CSF. A toll-free technical support service is available 24-hours/day for clinicians managing patients with Medtronic(R), SynchromMed(R), Drug Infusion System implants at 1-800-707-0933.
- Drug withdrawal: Withdrawal from oral baclofen can be managed by reinstituting the usual oral dose; intravenous benzodiazepines may also be useful. Withdrawal from chronic intrathecal baclofen may be particularly severe. Reinstitute intrathecal infusion if possible (fill pump, replace battery, etc) or baclofen may be administered by lumbar puncture. If intrathecal administration not possible, administer oral baclofen and supplement with intravenous benzodiazepines. Oral cyproheptadine may also be of benefit (Adult dose: 12 mg initially orally, then 2 mg every 2 hours if symptoms persist, maximum 32 mg/day. Pediatric dose: 0.25 mg/kg/day divided every 6 hours, maximum dose 12 mg/day).
- Monitoring of patient: Institute continuous cardiac monitoring and monitor vital signs frequently. Monitor mental status, adequacy of respirations and the ability to protect the airway. Monitor pulse oximetry. Monitor CPK in patients with prolonged seizures or coma. Monitor renal function and urine output in patients with prolonged seizures or coma, or hemodynamic instability.
- Hemodialysis: May be useful after severe overdose, particularly in patients with impaired renal function. Rarely indicated as most patients do well with supportive care.
- Patient disposition: HOME CRITERIA: Asymptomatic children with unintentional ingestions of less than 5 mg/kg can be observed at home. OBSERVATION CRITERIA: All patients with deliberate self-harm ingestion should be evaluated in a healthcare facility and monitored for 6 hours or until symptoms (vital sign abnormalities, agitation, hallucinations) resolve. Children with inadvertent ingestion of 5 mg/kg or more, or those who are symptomatic should be observed in a healthcare facility. ADMISSION CRITERIA: Admit patients with seizures, mental status depression, respiratory depression, delirium, or hypotension to an intensive care unit. CONSULT CRITERIA: Call a Poison Center for assistance in managing patients with severe toxicity or in whom the diagnosis is not clear.