Determination of Genotoxic Impurities in Pharmaceuticals

May 02, 2013
By LCGC Editors

The determination of genotoxic impurities (GIs) in drug substances and pharmaceutical products is an emerging topic in pharmaceutical quality control. GIs are intermediates or reactants in the synthetic pathway of a drug substance and should be monitored at ppm (μg/g drug substance) or even ppb (ng/g) levels. This is several orders of magnitude lower than in classical impurity analysis (0.05% or 500 ppm level) or in residual solvent analysis. Analytical methods for the determination of GIs include gas chromatography (GC) and liquid chromatography (LC), both often combined with mass spectrometry (MS) detection. Some typical examples of GIs trace analysis using GC and LC are presented. The potential of on-line reaction monitoring is also discussed.

Based on the threshold of toxicological concern (TTC) concept, the European Medicines Evaluation Agency (EMEA) published guidelines on the limits of genotoxic impurities in pharmaceutical ingredients (1). Impurities that contain a "structural alert functionality" (2) must be quantified at levels below the TTC, that corresponds to 1.5 μg daily intake (for lifetime exposure). In practice, this means that the genotoxic impurities must be monitored in the drug substance or pharmaceutical product at levels far below classical impurity determinations. Typically, methods should allow the determination of GIs (specific solute or group of solutes) at levels between 10 ng/g and 1000 ng/g drug substance (10–1000 ppb). Consequently, method development for trace analysis of potential genotoxic impurities is a challenge in pharmaceutical analysis.

A comprehensive overview of strategies to identify and control genotoxic impurities is described in a book recently published by Andrew Teasdale (3). This work includes chapters on regulatory guidelines, evaluation of the TTC concept, risk assessment and analytical methods, including innovative use of nuclear magnetic resonance (NMR). It is clear that methods such as NMR or direct analysis in real time (DART) in combination with mass spectrometry will increase in importance in the coming years. However, for the analysis of trace impurities in a matrix that can contain other impurities at concentration levels that are several orders of magnitude higher, the combination of a chromatographic separation with mass spectrometry (MS) (providing high sensitivity and selectivity) can still be considered as the present state-of-the-art approach for genotoxic analysis.

A short overview of chromatographic trace analysis methods for GIs is given and some typical cases are presented that illustrate the potential of state-of-the-art gas chromatography–mass spectrometry (GC–MS) and liquid chromatography–mass spectrometry (LC–MS). Finally, the use of GC–MS for on-line reaction monitoring is also discussed.

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