Intrathecal Baclofen Overdose: Report of 7 Events in 5 Patients and Review of the Literature

This study is intended to alert the clinician to the insidious symptoms of baclofen overdose, its prevention and treatment. In a group of 43 patients suffering from previously intractable spasticity and a total treatment time of 2,422 weeks, 7 events of intrathecal baclofen overdose happened in 5 patients. On two occasions, a bolus injection caused an overdose (dose 50 and 280-mu-g). The 5 events during continuous infusion intoxication only happened in high dosed patients. The overdose symptoms occurred in one patient when she was lying in supine position (800-mu-g/24 h), in another patient after repair of CSF leakage by an autologous epidural bloodpatch (1,920-mu-g/24 h) and in tolerant patients, once during maximal dose adjustments (2,400-mu-g/24 h) and twice ca. 6 hours following reinitiation of the intrathecal baclofen infusion after a "drug holiday" treatment (27 and 55-mu-g/h). We could not confirm the reported similarity of baclofen overdose with the anticholinergic syndrome. Especially, the bradycardia and hypotension are more in accord with the reported clinical picture of oral baclofen overdose. In the absence of a pure baclofen antagonist and the varying symptoms of intrathecal baclofen, intoxication make rational treatment difficult. We observed that the advised physostigmine therapy is not always effective and safe. The occasionally doubtful antidotal benefits of physostigmine must be weighed against major side-effects. The classical approach of decreasing the absorption of a drug by lowering baclofen levels in the CSF by lumbar puncture drainage was successful. This approach together with conservative symptomatic treatment in an intensive care environment is probably a better and safer alternative than physostigmine alone as an antidote.