Liquid chromatographic determination of paracetamol and dextropropoxyphene in plasma

Determination of paracetamol: historical evolution

Paracetamol is a common analgesic and antipyretic drug that is used for the relief of fever, headaches and other minor aches and pains. Their determination in pharmaceuticals is of paramount importance, since an overdose of paracetamol can cause fulminating hepatic necrosis and other toxic effects. Many analytical methodologies have been proposed for the determination of paracetamol. The aim of the present study is to evaluate the utility of different techniques for quantification of paracetamol content in pharmaceutical formulations and biological samples.

Simultaneous determination of paracetamol and dextropropoxyphene in human plasma by liquid chromatography/tandem mass spectrometry: application to clinical bioequivalence studies

A liquid chromatography/mass spectrometry method for simultaneous determination of paracetamol and dextropropoxyphene in human plasma is described. Paracetamol and dextropropoxyphene, together with their internal standards (tolbutamide and pyrroliphene), were extracted from 0.5 mL of plasma using solid-phase extraction. The chromatography was performed using a Thermo Hypersil APS-2 Amino column (250 mm x 4.6 mm, 5 microm) with a mobile phase consisting of acetonitrile and 0.4% glacial acetic acid in water (20:80). The total run time was 6 min for each sample. The triple-quadrupole mass spectrometer was operated in both positive (for detection of dextropropoxyphene and its IS pyrroliphene) and negative (for detection of paracetamol and its IS tolbutamide) modes using a polarity-switching technique. Multiple reaction monitoring was used for quantification. The method was linear over the concentration range of 0.1-20 microg/mL for paracetamol and 0.5-80 ng/mL for dextropropoxyphene. The intra- and inter-day precision were less than 10%, and the accuracy ranged from 92.2-110.9%. The lower limits of quantification were 0.1 microg/mL for paracetamol and 0.5 ng/mL for dextropropoxyphene. The present method provides a robust, fast and sensitive analytical tool for both paracetamol and dextropropoxyphene, and has been successfully applied to a clinical bioequivalence study in 14 subjects.

Influence of menstrual cycle on the pharmacokinetics of paracetamol through salivary compartment in healthy subjects

Hormonal changes during the different phases of menstrual cycle may influence drug disposition. The objective of this study was to investigate the influence of the menstrual cycle on the pharmacokinetics of paracetamol through salivary compartment in young healthy Indian women (n = 12) with regular menstrual cycles. The subjects received an oral dose of 1 g paracetamol on the 3rd, 13th, and 23rd days of their menstrual cycle in a 3 x 3 randomized crossover design. Saliva samples were collected at predetermined time intervals and the paracetamol content in them was estimated using an established HPLC method. The pharmacokinetics of paracetamol was worked out using a model-independent method employing WinNonlin 3.1. The mean Cmax of paracetamol was significantly (p < 0.05) lower (31.5%) in the ovulatory phase than in the follicular phase. The mean AUC0-t and AUC0-infinity values were significantly (p < 0.05) lower in the ovulatory phase than those in the luteal phase. These changes could be due to increased first-pass metabolism and decreased bioavailability of paracetamol during the ovulatory phase.

Rapid liquid chromatographic assay for the determination of acetaminophen in plasma after propacetamol administration: application to pharmacokinetic studies

A simple method for the rapid estimation of acetaminophen in plasma is described here. p-Propionamidophenol was used as internal standard. The assay involved a single ethyl acetate extraction and liquid chromatographic analysis at a wavelength of 242 nm using a reversed-phase encapped column, with a mobile phase of acetonitrile and 0.005 M potassium dihydrogen phosphate adjusted at pH 3.00. The limit of quantitation of acetaminophen by this method was 0.05 microg ml(-1), only 0.1 ml of the plasma sample was required for the determination. The calibration graph was linear from 0.05 to 100 microg ml(-1). Intra and inter-day precision (CV) did not exceed 8.93%. Mean recoveries of 90.31% with a CV of 1.38% were obtained. Applicability of the method was demonstrated by a pharmacokinetic study in normal volunteers who received 2 mg propacetamol.

Determination of dextropropoxyphene and norpropoxyphene in plasma by high-performance liquid chromatography

A simple and sensitive procedure for the routine assay of the analgesic drug dextropropoxyphene and its main metabolite, norpropoxyphene, in plasma is described. After liquid-liquid extraction from alkalinized plasma and back-extraction into a small volume of an acidic aqueous phase, the aqueous phase was injected into a column packed with 3-microns octadecylsilica particles. Ultraviolet absorbance detection at 210 nm was used. Concentrations down to 2 nM could be determined for both compounds; at this level, the intra-assay coefficient of variation was 5%.