title: Chemical stability of admixtures combining ziconotide with baclofen during simulated intrathecal administration.
abstract: Objective.  To determine the stability of admixtures combining ziconotide with commercially formulated or powdered baclofen during simulated intrathecal infusion under laboratory conditions at 37°. Materials and Methods.  Admixtures of ziconotide (25 µg/mL) with commercially formulated (1.5 mg/mL) or powdered (2.0 mg/mL) baclofen were stored in implantable intrathecal pumps at 37°. Drug concentrations were determined with high-performance liquid chromatography, and the length of time that the concentrations of both drugs remained ≥90% and ≥80% of initial (ie, the 90% and 80% stability, respectively) was estimated based on lower 95% confidence bounds obtained via linear regression. Results.  Baclofen was stable in both admixtures. In the commercially formulated baclofen admixture, the mean ziconotide concentration declined to 82.2% of initial in 30 days; the estimates for 90% and 80% stability were 12 and 29 days, respectively. In the powdered baclofen admixture, the mean ziconotide concentration declined to 87.4% of initial in 30 days; the estimates for 90% and 80% stability were 20 and 41 days, respectively. Conclusion.  Ziconotide-baclofen admixtures were more stable when prepared using powdered baclofen rather than a commercial baclofen formulation.
authors.affiliation: Elan Pharmaceuticals Inc., South San Francisco, CA, USA;              Gilead Inc., Foster City, CA, USA.
authors.forename: David
authors.initials: D
authors.lastname: Shields
authors.forename: Rick
authors.initials: R
authors.lastname: Montenegro
authors.forename: Jennifer
authors.initials: J
authors.lastname: Aclan