Study design: Retrospective study. Objectives: To study the incidence and management of tolerance in patients treated with intrathecal baclofen (ITB) therapy. Setting: Department of neurology and neurosurgery, University Medical Center Groningen, The Netherlands. Methods: Medical records of all patients who had received an implantable ITB pump at our clinic during 1991-2005 were reviewed. Results: A total of 37 patients (representing 116 pump years) were included. Mean follow-up time was 38 months (range 3-120 months). Baclofen dose increased in the first 18 months after implantation (Po0.05), and then stabilized around a mean dose of 350 mg per day. Eight patients (22%) developed tolerance, defined as a dose increase of 4100 mg per year. No predictive factors for development of tolerance could be determined. Three different treatment regimens for tolerant patients were analyzed. Altering the infusion mode from simple to complex continuous (n ¼ 6) had no effect on the development of tolerance. Pulsatile bolus infusion (n ¼ 1) and a drug holiday (n ¼ 2) were both effective in reducing the daily baclofen dose. Patients who needed surgical revision of the pump system because of mechanical failures (n ¼ 11) showed a significant dose decrease during the first month after revision, indicating that the preoperative dose increase most likely had been caused by the pump failure. Pumprelated complications occurred once per 10.5 years of ITB treatment. Drug-related side effects had an annual risk of 13.8%. The reported events were mostly mild. Conclusions: ITB therapy is effective and safe, also in the long term and causes tolerance in only 22% of the treated patients.

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