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Objective: Assess safety and tolerance of intravenous (IV) baclofen using a dog model. Design: Prospective pharmacokinetic study involving 6 adult dogs. Two dogs received baclofen 10 mg oral and IV bolus doses. Subsequent 4 dogs were given IV boluses of 0.5, 1.0 and 1.5 mg/kg followed by constant infusion of baclofen (rates of 0.1, 0.2 and 0.4 mg/kg/hour). Also, dogs were given single IV 2 and 3 mg /kg bolus doses. Outcome measures included clinical observation scales and baclofen levels. Results: Oral bioavailability was 0.66 and 0.69 in 2 dogs. Following IV baclofen, terminal phase half-lives were 3.3 and 3.6 hours. Single bolus doses of 2 and 3 mg/kg caused mild to moderate clinical changes which were delayed at least 2 hours after peak blood levels. Boluses of 0.5 and 1.0 mg/kg with constant infusion between boluses were tolerated, however within 30 minutes of beginning constant infusion of 0.2 mg/kg/hr after the second bolus (1.0 mg/kg), dogs showed progressive sedation and ataxia. Clinical improvement occurred within 7 hours of stopping baclofen. Dogs appeared normal by the next morning. Conclusions: IV baclofen bolus doses of 0.5 to 3 mg/kg were well tolerated. Maximum clinical effect was delayed for at least 2 hours after peak plasma levels. [ABSTRACT FROM AUTHOR]

Setting: Regional children's specialty hospital., Patient: 11 year old boy with a history of quadriparetic cerebral palsy (CP), shunted hydrocephalus, and continuous infusion of intrathecal baclofen (ITB) to treat hypertonicity., Case Description: The patient presented for a second opinion after experiencing three weeks of increased tone treated by shunt revision three times after two studies injecting contrast into the ITB pump catheter via the catheter access port did not demonstrate any extravasation of contrast material. Parents report that there was little change in his lower extremity tightness. His speech showed increased dysarthria during this time, and he had unusual difficulty with handling food. On evaluation, the patient had severely increased muscle tone. He also was noted to have palpable fluid in his pump pocket. Review of the X-rays that accompanied the patient revealed findings that caused us to be suspicious of a tear of the sleeve that is part of the mechanism that connects the intrathecal catheter to the pump. A 100 microgram bolus of ITB was administered, which did result in some relaxation.Assessment/Results: PATIENT underwent surgery at which time a torn pump-catheter connector was confirmed and replaced with a different type of connector. His symptoms resolved and he required a lower dose of ITB than on admission for significantly better tone control., Discussion: Individuals typically reach a stable dose of ITB and if they develop a need for increasing dose later, most frequently a catheter problem exists. Also, if there is fluid in the pump pocket, we have a high index of suspicion for this type of catheter/pump connector tear., Conclusion: In this case, careful evaluation of plain radiographs coupled with careful history taking, including the individual's response to interventions, was all that was necessary to make an accurate diagnosis.