Bioanalytical considerations for quantification of ondansetron in rat microdialysis study using LC-MS/MS.

Area of Science:

• Analytical Chemistry
• Pharmacokinetics
• Neuroscience

Background:

• Ondansetron, an anti-emetic, shows potential for treating neuropathic pain.
• P-glycoprotein (Pgp) at the blood-brain barrier may limit ondansetron's central nervous system penetration.
• Microdialysis is a technique to measure unbound drug concentrations in tissues and body fluids.

Purpose of the Study:

• To develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method.
• To quantify ondansetron concentrations in rat serum and brain microdialysates for pharmacokinetic analysis.
• To address the lack of a fully validated method for ondansetron in brain microdialysis studies.

Main Methods:

• Utilized a Gemini C18 column for chromatographic separation with a specific mobile phase.
• Serum samples underwent protein precipitation; microdialysates were diluted with an internal standard.
• Employed LC-MS/MS for sensitive and specific quantification of ondansetron.

Main Results:

• The method requires minimal sample volumes (2.5 μL serum, 15-20 μL microdialysate) enabling frequent sampling.
• Achieved a low limit of quantification (0.01 μg/mL in serum, 0.025 ng/mL in microdialysate).
• Artificial cerebrospinal fluid (aCSF) proved a suitable surrogate matrix, despite observed ion suppression.

Conclusions:

• The developed LC-MS/MS method fulfills FDA and EMA validation criteria.
• Successfully applied to a pilot in vivo pharmacokinetic study in rats.
• The method is sensitive for low brain concentrations and versatile for high serum concentrations of ondansetron.