Development and validation of a UPLC-MS/MS method for real-time neuropharmacokinetic monitoring of iboga alkaloids in rat brain.

Abstract

Iboga alkaloids, including ibogaine, its primary metabolite noribogaine, and the naturally occurring congener ibogamine, have shown promise for the treatment of substance use and other neuropsychiatric disorders but are limited by cardiotoxic effects. Safer synthetic analogs, such as oxa-noribogaine, are under active development; however, validated analytical methods for quantifying these compounds in brain extracellular fluid are lacking. Existing approaches that rely on tissue homogenate analysis reflect total tissue drug content, encompassing intracellular, protein-bound, and vascular compartments, and cannot directly measure pharmacologically active, unbound drug at the site of receptor interaction. Here, we report the development and validation of a sensitive UPLC-MS/MS method capable of quantifying ibogaine, noribogaine, ibogamine, and oxa-noribogaine in rat brain microdialysate. Using D2-noribogaine, a custom-synthesized isotopically labeled internal standard, the method achieved lower limits of quantification of 0.78-1.56 ng/mL with a 6-minute run time. Calibration curves were linear over 0.78-75 ng/mL for ibogamine and 1.56-75 ng/mL for ibogaine, noribogaine, and oxa-noribogaine, and intra- and inter-day accuracy and precision met acceptance criteria for all analytes. Analytes were stable under freeze-thaw, long-term storage (-80°C), and autosampler conditions. The method was successfully applied to measure noribogaine levels in the nucleus accumbens following intraperitoneal administration (10 mg/kg) in rats (n = 4), yielding a recovery-corrected peak unbound extracellular fluid (ECF) concentration (C_max,u) of 292 ± 68 ng/mL (∼0.98 µM) at a mean T_max of 50 min, demonstrating the method's suitability for real-time neuropharmacokinetic profiling of iboga alkaloids in brain ECF. This validated method provides an essential preclinical tool for pharmacokinetic-pharmacodynamic characterization of iboga alkaloids at their sites of therapeutic action, supporting the development of safer iboga-derived therapeutics.

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