Etodolac linearity

A colorimetric method for the analysis of etodolac has been reported which is based on the formation of colored complexes with p-dimethyl-aminobenzaldehyde in the presence of sulfuric acid and ferric chloride [19]. Absorbance measurements were made at 591.5 nm, and the method was found to be linear over the concentration range of 10 to 80 pg/mL. This method was used to determine etodolac in bulk powder and other dosage forms. 

A simple, sensitive, and reproducible fluorimetric method for the determination of etodolac in bulk powder or dosage forms has been reported [19]. The method involves measurement of the native fluorescence at a wavelength of 345 nm, when ethanolic solutions of the drug were excited at 235 nm. The calibration was found to be linear over the concentration range of 96 to 640 ng/mL. 

A sensitive reverse-phase HPLC method has been developed for the analysis of etodolac in tablet formulation [22]. The chromatographic separation was achieved using a reverse-phase Cu column, having dimensions of 3.3 cm x 0.46 cm i.d. (3 pm particles) and which was maintained at 30°C. The mobile phase consisted of pH 6.0 phosphate buffer / methanol (60 40 v/v), and was eluted at 1 mL/min. Analyte detection was effected on the basis of UV detection at 230 nm. Diazepam was used as an internal standard. The sample preparation entailed grinding the etodolac tablets, followed by extraction with methanol (using sonication). A retention time of 1.46 min was obtained for etodolac under these conditions, and the method was found to be linear, precise, and accurate over the concentration range of 0.01 to 0.1 mg/mL. 

A simple, accurate, and reproducible HPLC method has been developed to determine etodolac in presence of impurities (1-methyl and 8-methyl-etodolac) and in pharmaceutical formulations [14]. A Viospher ODS-2 (15 cm x 4.6 mm i.d., 5 pm particle size) HPLC column was used as stationary phase, and acetonitrile/0.05 M phosphate buffer (pH 4.75) (60 40 v/v) eluted at 0.8 mL/min was used as mobile phase. The system was thermostatted to 25 °C, and acetaminophen was used as an internal standard. Detection was achieved by measurement of the UV absorbance at 229 nm. The method was found to be linear over the concentration range of 2-20 pg/mL. The relative retention times for etodolac and acetaminophen were 2.2 and 2.9 min respectively. The retention times for the two impurities, 1-methyl-etodolac and 8-methyl-etodolac, were 1.4 and 3.8 min respectively. 

An isocratic HPLC method for screening plasma samples for sixteen different non-steroidal anti-inflammatory drugs (including etodolac) has been developed [29]. The extraction efficiency from plasma was 98%. Plasma samples (100-500 pL) were spiked with internal standard (benzoyl-4-phenyl)-2-butyric acid and 1 M HC1 and were extracted with diethyl ether. The organic phase was separated, evaporated, the dry residue reconstituted in mobile phase (acetonitrile-0.3% acetic acid-tetrahydrofuran, in a 36 63.1 0,9 v/v ratio), and injected on a reverse-phase ODS 300 x 3.9 mm i.d. column heated to 40°C. A flow rate of 1 mL/min was used, and UV detection at 254 nm was used for quantitation. The retention time of etodolac was 30.0 minutes. The assay was found to be linear over the range of 0.2 to 100 pg/mL, with a limit of detection of 0.1 pg/mL. The coefficients of variation for precision and reproducibility were 2.9% and 6.0%, respectively. Less than 1% variability for intra-day, and less than 5% for inter-day, in retention times was obtained. The effect of various factors, such as, different organic solvents for extraction, pH of mobile phase, proportion of acetonitrile and THF in mobile phase, column temperature, and different detection wavelengths on the extraction and separation of analytes was studied. 

The mobile phase was 0.05 M pH 4 phosphate buffer / acetonitrile (55 45, v/v) at a flow rate of 1.3 mL/min. Detection was carried out at 220 nm with a UV detector. The retention times were 12.5 and 16.9 minutes for etodolac and ibuprofen, respectively. The method was linear over a concentration range of 0.125 to 10.0 pg/mL. The recovery of etodolac was 93.9 % ( 5.3 %). Detailed methods for the analysis of metabolites of etodolac were also provided. 

An HPLC method for the analysis of etodolac and its metabolites in equine serum and urine was developed [32]. Serum (1 mL) or urine (0.5 mL) samples were extracted with iso-octane/isopropanol (95 5, v/v) after addition of ibuprofen as internal standard, diluting with 1 or 2 mL of distilled water, and adjusting the pH to 1 with 1 M HC1. The organic layer was evaporated under a stream of nitrogen, the residue dissolved in 100 pL of mobile phase, and a 20 pL aliquot injected on to the HPLC system. The HPLC system consisted of a pre-column, a 250 x 4 mm (7 pm particles) LiChrosorb RP-18 column at 25°C, isocratic elution with 1% acetic acid/acetonitrile (50 50, v/v) at a flow rate of 1.3 mL/min, and UV detector at 227 nm. The retention time of etodolac was 8.5 minutes. The method was linear over the range of 0.1-20 pg/mL in serum, and in 0.5-800 pg/mL range in urine. The limits of quantitation were 40 ng/mL in... 

A GS-MS method for the analysis of etodolac in human plasma has been developed [16]. Plasma samples were spiked with meclofenamic acid (the internal standard), acidified with 5N HC1, and extracted twice with chloroform / dichloromethane / hexane (50 25 25, v/v). The organic phase was evaporated, the residue methylated with ethereal diazomethane, dried again, and reconstituted in hexane. Analytical separation was performed on a 15 m x 0.24 mm i.d., 0.25 pm film thickness, fused silica capillary column. The oven temperature was variable (150 to 260°C) and the injector was at 260°C. The carrier gas was helium at 1 mL/min. Mass spectra were obtained using positive electron impact ionization (70 eV) at m/z 228 for etodolac. The method was linear in the 1-10 ng/mL (low) and 10-100 ng/mL (high) concentration range. The detection limit was 0.5 ng/mL in plasma, and recovery of etodolac from plasma sample exceeded 92%. 

The gas flow rates were helium 2 mL/min hydrogen 3 mL/min air 50 mL/min. The column head pressure was maintained at 0.85 bar. GC peaks representing diastereomers of (+)- and (-)-etodolac eluted at 17.5 and 19.8 min, respectively. The derivatized internal standard had a retention time of 12.5 min. The calibration curves for each enantiomer were linear over the concentration range of 0.25 - 20 pg/mL. The minimum quantifiable concentration of each enantiomer was 50 ng/mL, with observed coefficients of variation being within 8%. The recoveries from plasma for (+)- and (-)-etodolac at concentrations of 2.5 pg/mL were 66.50 0.04% and 65.83 0.03%, respectively. 

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