1. Separation and quantitation of the S-(+)-enantiomer in the bulk drug tiagabine x HCl by chiral high-performance-liquid chromatography using a Chiralcel-OD column
A M Rustum, V Estrada J Chromatogr B Biomed Sci Appl. 1998 Jan 23;705(1):111-7. doi: 10.1016/s0378-4347(97)00388-5.
Tiagabine x HCl is being developed as an anti-convulsant/anti-epileptic agent for seizure disorders. The pharmacological activity of the R-(-)-enantiomer is higher than that of the S-(+)-enantiomer. Therefore, the drug is synthesized in the pure R-(-)-enantiomeric form. The enantiomers of tiagabine x HCl were separated on a modified cellulose stationary phase (Chiralcel-OD) with a mobile phase of hexane-isopropanol-ethanol (80:14:06, v/v/v). Approximately 5 ml of trifluoroacetic acid was added for each liter of the mobile phase mixture. The method is capable of separating the two enantiomers with a selectivity factor of 1.55 and a resolution factor of 3.4. The samples of tiagabine x HCl were monitored by a UV detector at 260 nm. The method was validated by conducting standard addition and recovery of the S-(+)-enantiomer in tiagabine x HCl. The R.S.D. of the method is 3.2%. The limit of quantification (LOQ) of the S-(+)-enantiomer present in tiagabine x HCl is about 0.03%.
2. A validated chiral LC method for the enantioselective analysis of Levetiracetam and its enantiomer R-alpha-ethyl-2-oxo-pyrrolidine acetamide on amylose-based stationary phase
B M Rao, R Ravi, B Shyam Sundar Reddy, S Sivakumar, I Gopi Chand, K Praveen Kumar, P V R Acharyulu, G Om Reddy, M K Srinivasu J Pharm Biomed Anal. 2004 Sep 3;35(5):1017-26. doi: 10.1016/j.jpba.2004.03.015.
A new, simple chiral HPLC method was developed for the enantiomeric separation of Levetiracetam, [(S)-alpha-ethyl-2-oxo-pyrrolidine acetamide], an antiepileptic drug in pharmaceutical formulations and in bulk materials. Enantiomeric separation was achieved on a chiralpak AD-H column using a mobile phase consisting of hexane and isopropanol in the ratio (90:10, v/v) at a flow rate of 1.0 ml/min. The resolution between the enantiomers was found to be not less than 7 in the optimized method. Interestingly, unwanted enantiomer, namely R-alpha-ethyl-2-oxo-pyrrolidine acetamide ((R)-enantiomer), was eluted prior to its mirror image in the developed method. The developed method was found to be selective in the presence of related impurities of Levetiracetam, namely N-(1-carbamoyl-propyl)-4-chloro-butyramide (Imp-1) and 1-ethyl-2-oxo-1-pyrrolidine acetic acid (Imp-2), and also under exposed conditions of UV light and 60 degrees C. The limit of detection (LOD) and limit of quantification (LOQ) of (R)-enantiomer were found to be 900 and 2250 ng/ml, respectively, for 10 microl injection volume. The method precision for (R)-enantiomer at limit of quantification level was within 8% R.S.D. Calibration curve for (R)-enantiomer was linear over the studied ranges (2250-9000 ng) with correlation coefficient greater than 0998. The active pharmaceutical ingredient was extracted from its finished dosage form (tablet) using isopropanol. The percentage recoveries of (R)-enantiomer were ranged from 94.2 to 102.6 and from 93.5 to 104.1 in spiked bulk and formulation samples of Levetiracetam, respectively. Levetiracetam sample solution and mobile phase are found to be stable for at least 48 h. The developed method was found to be rugged and robust. The proposed method was found to be suitable and accurate for the quantitative determination of (R)-enantiomer in bulk drugs and commercial formulations. Chiralcel OD-H column can also be used as an alternative column for the above purpose.
3. Gas chromatography-mass spectrometry assay method for the therapeutic drug monitoring of the antiepileptic drug tiagabine
D F Chollet, E Castella, L Goumaz, G Anderegg J Pharm Biomed Anal. 1999 Nov;21(3):641-6. doi: 10.1016/s0731-7085(99)00167-3.
A gas chromatography-mass spectrometry assay method suitable for the therapeutic drug monitoring of the antiepileptic drug tiagabine is described. Tiagabine and its desmethylated analogue used as internal standard were first extracted from serum by liquid-liquid extraction using an ethyl ether-isobutanol 98:2 mixture. Tiagabine and the internal standard were then methylated in the organic phase in presence of methanol by means of a safe and stable diazomethane derivative. After evaporation, the reconstituted extracts were chromatographed on a crosslinked phenyl methyl siloxane capillary column and detected by mass fragmentometry at m/z = 156. No other antiepileptic drug possibly administrated in polytherapy and no metabolite were found to interfere in the assay. The limit of quantification was 5 ng/ml. The precision and the accuracy were found to be suitable for the therapeutic drug monitoring of tiagabine.
