Stereoselective determination of demethyl- and didemethyl-citalopram in rat plasma and brain tissue by liquid chromatography with fluorescence detection using precolumn derivatization

Analytical methodologies for the enantiodetermination of citalopram and its metabolites

Citalopram (CIT) is a highly selective serotonin reuptake inhibitor (SSRI) frequently used in the treatment of major depressive disorders. It has a chiral centre in its structure and is used in therapy both as a racemic mixture (R,S-CIT) and a pure enantiomer (S-CIT). The differences between the pharmacokinetic and pharmacological profiles of the two enantiomers are well established. Consequently, the development of new efficient chiral analysis methods for their enantiomeric separation is a topic of great actuality. CIT metabolism is stereoselective as it is metabolized in chiral active metabolites, which retain considerable SSRI activity and contribute to the pharmacological effect. Chiral analytical methods are employed for the determination of enantiomeric ratio in pharmaceutical preparations and for monitoring the enantiomer levels in biological samples for therapeutic and toxicologic purposes. The current study reviews the published literature for the chiral analysis of CIT and its metabolites based on chromatographic and electrophoretic methods coupled with UV, fluorescence and mass spectrometry detectors.

Micellar liquid chromatographic method for the simultaneous determination of citalopram hydrobromide with its two demethylated metabolites. Utility as a diagnostic tool in forensic toxicology

A micellar liquid chromatographic method has been developed for the simultaneous determination of citalopram hydrobromide (CTA) with its two demethylated metabolites namely; desmethyl citalopram hydrochloride (DCTA) and didesmethyl citalopram tartrate (DDCTA). Separation was conducted on a C18 column using a mobile phase composed of 0.18 M sodium dodecyl sulphate (SDS), 15% 1-propanol, 0.3% tri-ethylamine, adjusted to pH 4 with 0.2 M o-phosphoric acid and adopting UV detection at 240 nm. Analysis was performed at 60 °C applying a flow rate of 2 mL/min. The proposed method was linear over the concentration ranges of 1.0-200.0, 0.6-200.0, and 0.5-200.0 μg/mL for CTA, DCTA, and DDCTA respectively, with corresponding limits of detection (LOD) of 0.5, 0.4, and 0.3 μg/mL and limits of quantification (LOQ) of 0.8, 0.5, and 0.4 μg/mL. The method was fully validated which allowed its application for the determination of CTA in its tablets. Moreover, the proposed method was extended to assay CTA with its metabolites in rat tissue organs samples which allowed the method to be used as a diagnostic tool in forensic toxicology.

Stereoselective determination of citalopram and desmethylcitalopram in human plasma and breast milk by liquid chromatography tandem mass spectrometry

A high performance liquid chromatography (HPLC) tandem mass spectrometry (MS/MS) method was developed for the simultaneous, stereoselective quantification of the antidepressant citalopram and its active metabolite desmethylcitalopram in human plasma and breast milk. Sample preparation was performed by a two-step approach, including generic protein precipitation with acetonitrile followed by solid phase extraction. Enantiospecific separation of analytes was achieved on a Phenomenex^® Lux Cellulose-2 column (4.6mm×150mm; 5μm), using reversed phase chromatography conditions characterized by a gradient elution of ammonium acetate buffer (pH 9.0; 20mM) and acetonitrile at a flow rate of 0.6ml/min. The compounds were detected by a tandem quadrupole mass spectrometer equipped with an electrospray ionization source and operating in multiple reaction monitoring mode. The method was fully validated in both biological fluids over a large concentration range of 0.1-100ng/ml for S-(+)- and R-(-)-citalopram, and 0.3-100ng/ml for S-(+)- and R-(-)-desmethylcitalopram. Trueness (90.0-113.3% and 97.1-103.6%), repeatability (0.9-15.9% and 0.9-8.4%) and intermediate precision (1.3-17.8% and 0.9-9.6%) in plasma and breast milk, respectively, meet international guidelines for method validation. Internal standard-normalized matrix effects ranged between 99 and 101% and 98-105%, respectively. The accuracy profiles (total error of trueness and precision) were mostly within the acceptance limits for biological samples defined as ±30%. The method was successfully applied to patient samples in a clinical trial setting.

Enantiomeric fraction as an indicator of pharmaceutical biotransformation during wastewater treatment and in the environment--a review

Enantioselective analysis of some pharmaceuticals during wastewater treatment has the potential to reveal significant insights regarding the effectiveness of biotransformation processes. Furthermore, enantioselective analysis of chiral pharmaceuticals in the aquatic environment may provide a useful historical record revealing the dominant source of (treated or untreated) wastewater contamination. This review of the recent scientific literature has identified only a handful of studies that have directly investigated these promising applications. However, a range of enantioselective analytical techniques are likely to be adaptable from those which have been developed within the pharmaceutical industry. These include direct enantioseparations of enantiomers on chiral stationary phases as well as indirect separations by achiral stationary phases after chiral derivatization to form pairs of physically distinguishable diastereomers. Further investigations of the patterns of enantiomeric fractionation of pharmaceuticals in wastewater and environmental samples will provide an increasingly solid understanding of the relationship between biotransformation processes and the often overlooked parameter of enantiomeric fraction.

Chiral separations

The main goal of this review is to provide a brief overview of chiral separations to researchers who are versed in the area of analytical separations but unfamiliar with chiral separations. To researchers who are not familiar with this area, there is currently a bewildering array of commercially available chiral columns, chiral derivatizing reagents, and chiral selectors for approaches that span the range of analytical separation platforms (e.g., high-performance liquid chromatography, gas chromatography, supercritical-fluid chromatography, and capillary electrophoresis). This review begins with a brief discussion of chirality before examining the general strategies and commonalities among all of the chiral separation techniques. Rather than exhaustively listing all the chiral selectors and applications, this review highlights significant issues and differences between chiral and achiral separations, providing salient examples from specific classes of chiral selectors where appropriate.

Metabolite identification in rat brain microdialysates by direct infusion nanoelectrospray ionization after desalting on a ZipTip and LTQ/Orbitrap mass spectrometry

Analyzing brain microdialysate samples by mass spectrometry is challenging due to the high salt content of the artificial cerebral spinal fluid (aCSF), low analyte concentrations and small sample volumes collected. A drug and its major metabolites can be examined in brain microdialysates by targeted approaches such as selected reaction monitoring (SRM) which provides selectivity and high sensitivity. However, this approach is not well suited for metabolite profiling in the brain which aims to determine biotransformation pathways. Identifying minor metabolites, or metabolites that arise from brain metabolism, remains a challenge and, for a drug in early discovery, identification of metabolites present in the brain can provide useful information for understanding the pharmacological activity and potential toxicological liabilities of the drug. A method is described here for rapid metabolite profiling in brain microdialysates that involves sample clean-up using C18 ZipTips to remove salts followed by direct infusion nanoelectrospray with an LTQ/Orbitrap mass spectrometer using real-time internal recalibration. Full scan mass spectra acquired at high resolving power (100 K at m/z 400) were examined manually and with mass defect filtering. Metabolite identification was aided by sub-parts-per-million mass accuracy and structural characterization was accomplished by tandem mass spectrometry (MS/MS) experiments in the Orbitrap or LTQ depending on the abundance of the metabolite. Using this approach, brain microdialysate samples from rats dosed with one of four CNS drugs (imipramine, reboxetine, citalopram or trazodone) were examined for metabolites. For each drug investigated, metabolites, some of which not previously reported in rat brain, were identified and characterized.

Chiral determination of antidepressant drugs and their metabolites in biological samples

The determination of chiral drugs and their metabolites in biological samples is key to gaining a full understanding of enantioselective drug action and disposition, as well as establishing the advantages of using racemate or isolated enantiomers. In this review, methods published in the last 8 years regarding the analysis of chiral antidepressant drugs and their metabolites in biological fluids (e.g., plasma, urine and cerebrospinal fluid) are reviewed. The importance and interest in analyzing the enantiomers of the active compound and its metabolites in biological samples are also discussed.