Stereo-specific LC and LC-MS bioassays of antidepressants and psychotics.

Stereochemistry in drug action is gaining importance because the enantiomers often differ in their biological activity and pharmacokinetic profiles. The use of racemic drugs may contribute to adverse effects owing to the presence of either inactive or toxic enantiomers. Most of the drugs currently used to treat psychiatric disorders, including depression, contain one or more chiral centers and are mostly sold as racemates. Single-enantiomer drugs provide greater selectivity for their biological targets, improved therapeutic indices and better pharmacokinetics compared with racemates. Therefore it is of great importance to monitor body fluid/tissue levels of drugs used to treat depression and psychiatric disorders. The present manuscript gives an overview of liquid chromatographic and mass spectrometric techniques reported during 2000-2013 for enantiomeric separation of various classes of antidepressants, viz. selective serotonin reuptake inhibitors, serotonin and norepinephrine reuptake inhibitors, noradrenergic and specific serotonergic antidepressants, norepinephrine reuptake inhibitors, norepinephrine-dopamine reuptake inhibitors, nonamphetamine central nervous system stimulants, serotonin and dopamine inhibitors and γ-aminobutyric acid receptor agonists in biological matrices. Techniques used for extraction, separation and quantification are discussed.

LC-Q-TOF-MS/MS determination of darunavir and its metabolites in rat serum and urine: application to pharmacokinetics.

A simple, rapid and reliable liquid chromatography coupled with quadrupole time of flight mass spectrometry (LC-Q-TOF-MS/MS) method was developed and validated for simultaneous determination of darunavir and its metabolites in rat serum and urine. The separation was accomplished on an Agilent RP-18 (250×4.6mm, 5µm) column using 20mM ammonium acetate and methanol (40:60, v/v) as a mobile phase at a flow rate of 1.0mL/min in an isocratic mode. The [M+H](+) ions of darunavir (m/z 548) and metabolites-I (m/z 392) were monitored in positive mode of ionization, while [M-H](-) ion of metabolite-II (m/z 172) in negative mode selectively. The matrix effects of rat serum and urine were found to be negligible and the recoveries were 87-93% for all the analytes. The short and long term stability of darunavir and its metabolites was within acceptable limits and the lower limits of quantification were in the range of 3.63-5.24ng/mL with a linear range of 5-5000ng/mL in rat serum as well as urine. The method exhibited good intra- and inter-day performance in terms of 2.54-8.92% precision and 0-5% accuracy. The method was successfully applied to a single-dose pharmacokinetic study of darunavir boosted with ritonavir in Wistar rats.

Determination of gemifloxacin on dried blood spots by hydrophilic interaction liquid chromatography with fluorescence detector: application to pharmacokinetics in rats.

A highly selective, sensitive and rapid hydrophilic liquid interaction chromatographic method was developed and validated for determination of gemifloxacin on dried blood spots. The chromatographic separation was achieved on a reversed-phase zwitterionic hydrophilic interaction liquid chromatographic ZIC®HILIC-C18 (4.6 × 100 mm; 5 µm) column using acetonitrile-10 mM ammonium acetate (pH 3.5; 80:20, v/v) as a mobile phase in an isocratic elution mode at a flow rate 0.6 mL/min at 27 °C. An on-line fluorescence detector set at excitation and emission wavelengths of 269 and 393 nm, respectively was used for monitoring column eluents. Ciprofloxacin was used as an internal standard. The method was validated for accuracy, precision, linearity and selectivity by design of experiments following ICH guidelines. The assay exhibited a linear range of 25-5000 ng/mL for gemifloxacin on dried blood spots. The lower limit of detection was found to be 10 ng/mL. The intra- and inter-assay coefficients of variation did not exceed 7.4% deviation of the nominal concentration. The recovery of GFX from dried blood spots was >95.0% and its stability was excellent with no evidence of degradation during sample processing for at least 3 months storage in a freezer at -20 °C.

Development of a validated liquid chromatographic method for determination of related substances of telmisartan in bulk drugs and formulations.

A simple and rapid reversed phase liquid chromatographic method for separation and determination of the related substances of telmisartan (TLM) was developed and validated. The chromatographic separation was achieved on Lichrospher RP-18 column (250 × 4.6 mm, 5 µm), using 20 mM ammonium acetate containing 0.1% (v/v) triethylamine (pH adjusted to 3.0 with trifluoroacetic acid) and acetonitrile as mobile phase at 25°C. The detection was performed at 254 nm. The method was validated and found to be robust, precise, specific and linear between 0.37 and 500 µg/mL. The limits of detection and quantification of telmisartan were 0.11 and 0.37 µg/mL, respectively. The method was successfully applied to quantify related substances and assay of TLM in bulk drugs and commercial tablets. The related substances relate to a novel synthetic route and different from those A-H impurities reported by European Pharmacopeia.