Development of chromatographic methods for the determination of genotoxic impurities in cloperastine fendizoate

Abstract

The classification of an impurity of a drug substance as genotoxic means that the “threshold of toxicological concern” (TTC) value of 1.5 μg/day intake, considered to be associated with an acceptable risk, should be the admissible limit in the raw material and that leads to new analytical challenges. In this study, reliable chromatographic methods were developed and applied as limit tests for the control of three genotoxic impurities (GTIs) in cloperastine fendizoate, drug widely used as an antitussive active pharmaceutical ingredient (API). In particular, GC–MS was applied to the determination of one alkyl halide (2-chloroethanol, 2-CE), while HPLC-DAD was selected for the analysis of two sulfonate esters (methyl p-toluenesulfonate, MPTS, and 2-chloroethyl p-toluenesulfonate, CEPTS). Regarding GC–MS, strong anion-exchange (SAX)-SPE was applied to remove fendizoate from the sample solutions, due its low volatility and its high amount in the raw material. The GC–MS analysis was performed on a Factor Four VF-23ms capillary column (30 m × 0.25 mm I.D., film thickness 0.25 μm, Varian). Single ion-monitoring (SIM) detection mode was set at m/ z 80. In the case of HPLC-DAD, a suitable optimization of the chromatographic conditions was carried out in order to obtain a good separation of the impurity peaks from the drug substance peaks. The optimized method utilizes a SymmetryShield RP 8 column (250 mm × 4.6 mm, 5 μm, Waters) kept at 50 °C, with phosphate buffer (pH 3.0; 10 mM)–methanol (containing 10% ACN) (45:55, v/v) as the mobile phase, at the flow-rate of 1.7 mL/min and UV detection at 227 nm. The required sensitivity level was achieved by injecting 80 μL of sample solution, purified from fendizoate by SAX-SPE, followed by a 1:1 (v/v) dilution of the SPE eluate with water. For both GC–MS and HPLC-DAD, the method validation was performed in relation to specificity and limit of detection (LOD), as required by ICH guidelines in relation to limit assays. The developed methods were successfully applied for the determination of GTIs in five different batches of cloperastine fendizoate. In all the analyzed batches, the three target GTIs were below the concentration limit.