A pharmacokinetic-pharmacodynamic model for intrathecal baclofen in patients with severe spasticity.

AIMS: Intrathecal baclofen (ITB) has proven to be an effective and safe treatment for severe spasticity. However, although ITB is used extensively, clinical decisions are based on very scarce pharmacokinetic-pharmacodynamic (PKPD) data. The aim of this study was to measure baclofen CSF concentrations and clinical effects after administration of various ITB boluses in patients with spasticity and to create a PKPD model for ITB. METHODS: Twelve patients with severe spasticity received four different bolus doses of ITB (0, 25, 50, 75 µg and an optional dose of 100 µg), administered via a catheter with the tip at thoracic level (Th) 10. After each bolus, 10 CSF samples were taken at fixed time intervals, using a catheter with the tip located at Th12. Clinical effect was assessed by measuring spasticity with the Modified Ashworth Scale (MAS). These data were used to develop a PKPD model. RESULTS: All patients achieved an adequate spasmolytic effect with ITB doses varying from 50 to 100 µg. No serious side effects were observed. CSF baclofen concentrations, as well as the clinical effects, correlated significantly with ITB doses. The PK model predicted a steep spinal concentration gradient of ITB along the spinal axis. The clinical effect could be predicted using a delayed-effect model. CONCLUSIONS: ITB is an effective and safe therapy with, however, a steep concentration gradient along the spinal axis. This means that the administered baclofen is staying mainly around the catheter tip, which stresses the importance to position the ITB catheter tip closely to the targeted spinal level.

Tolerance to continuous intrathecal baclofen infusion can be reversed by pulsatile bolus infusion.

STUDY DESIGN: Pilot study. OBJECTIVE: To study the effect of pulsatile bolus infusion of intrathecal baclofen (ITB) on daily ITB dose, in patients showing dose increases, probably due to tolerance. SETTING: Department of neurology and neurosurgery, University Medical Center Groningen, the Netherlands. METHODS: Data on dosages and clinical efficacy were gathered from four patients who were switched from continuous to pulsatile bolus infusion of ITB, because of the probable diagnosis of tolerance to ITB. RESULTS: Switching from continuous to pulsatile bolus infusion resulted in a decrease of the daily ITB dose, while the clinical effect could be kept stable, without introducing adverse events. CONCLUSION: Pulsatile bolus infusion of ITB seems to be an effective and safe treatment strategy to reverse the need for increasing ITB dosages in patients with the probable diagnosis of tolerance to ITB.

The incidence and management of tolerance in intrathecal baclofen therapy.

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 (P<0.05), and then stabilized around a mean dose of 350 microg per day. Eight patients (22%) developed tolerance, defined as a dose increase of >100 microg 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=6) had no effect on the development of tolerance. Pulsatile bolus infusion (n=1) and a drug holiday (n=2) were both effective in reducing the daily baclofen dose. Patients who needed surgical revision of the pump system because of mechanical failures (n=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. Pump-related 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.