Estimation of serum indomethacin at therapeutic levels by means of thin-layer chromatography and spectrophotometry

Sensitive fused-silica capillary gas chromatographic assay using electron-capture detection for indomethacin in ovine fetal fluids

A sensitive gas chromatographic (GC) method with electron-capture detection (ECD) has been developed to quantitate indomethacin (IND) in plasma, urine, amniotic, and tracheal fluids obtained from the pregnant sheep model. IND and the internal standard, alpha-methylindomethacin (alpha-Me-IND) are extracted by a simple liquid-liquid extraction procedure using ethyl acetate and derivatized with N-methyl-N-(tert.-butyldimethyl-silyl)trifluoroacetamide (MTBSTFA) at 60 degrees C for 50 min. The limit of quantitation (LOQ) is 1 ng/ml with a C.V. < 10% and signal-to-noise ratio > 10. Recoveries from all fluids were greater than 80%. Calibration curves were linear over the range of 1-32 ng/ml with a coefficient of determination (r2) > 0.999. Inter- and intra-day coefficients of variation were < 10% at concentrations of 2-32 ng/ml, and < 20% at the LOQ. Applicability of the developed method is demonstrated for a pharmacokinetic study of IND samples collected following long-term infusion of IND in a chronically instrumented ovine fetus.

Determination of indomethacin, its metabolites and their glucuronides in human plasma and urine by means of direct gradient high-performance liquid chromatographic analysis. Preliminary pharmacokinetics and effect of probenecid

Indomethacin is metabolized in humans by O-demethylation, and by acyl glucuronidation to the 1-O-glucuronide. Indomethacin, its metabolite O-desmethylindomethacin (DMI) and their conjugates can be measured directly by gradient high-performance liquid chromatographic analysis without enzymic deglucuronidation. The glucuronide conjugates were isolated by preparative HPLC from human urine samples. In plasma only indomethacin was present. No isoglucuronides were present in acidic urine of the volunteer. The possible metabolite deschlorobenzoylindomethacin (DBI) was not detectable in urine. Calibration curves were constructed by enzymic deconjugation of samples containing different concentrations of isolated indomethacin acyl glucuronide, DMI acyl glucuronide and DMI ether glucuronide. The limit of quantitation of indomethacin in plasma is 0.060 microgram/ml. The limits of quantitation in urine are: indomethacin 0.053 microgram/ml, DMI 0.065 microgram/ml, DMI acyl glucuronide 0.065 microgram/ml and DMI ether glucuronide 0.254 microgram/ml. A pharmacokinetic profile of indomethacin is shown, and some preliminary pharmacokinetic parameters of indomethacin obtained from one human volunteer are given. Probenecid inhibits the formation of both the ether and the acyl glucuronide of DMI.

High-performance liquid chromatographic analysis of indomethacin in serum

A rapid high-performance liquid chromatographic (HPLC) method for quantitative determination of indomethacin in serum is described. The assay was performed after single extraction of indomethacin and itraconazole (internal standard) from serum using diethyl ether and eluted from a 4 micron C-18 reversed-phase column at ambient temperature. The mobile phase consisted of ethanol:water:glacial acetic acid (65:34:1, v/v) pumped isocratically at a flow rate of 1.3 ml/min. The effluent was monitored at 254 nm. Quantification was achieved by the measurement of the peak area ratio, and the absolute recoveries ranged from 94 to 97%. Within-day coefficients of variation (CV) ranged from 2.72 to 5.70% and between-day CV varied from 3.61 to 6.1%. Stability testing indicated that indomethacin is stable for at least 30 days in serum at -20 degrees C. The method was used to study indomethacin pharmacokinetics in rabbits.

Plasma indomethacin assay by reversed-phase ion pair high pressure liquid chromatography

A new rapid, selective and sensitive high pressure liquid chromatographic (HPLC) assay for indomethacin in plasma is described. The method involves precipitation of proteins with perchloric acid, followed by dichloromethane extraction using flurbiprofen as an internal standard. The organic solvent was evaporated and the residue dissolved in a water-methanol (2 + 3) phosphate buffer mixture with an apparent pH of 6.8. Aliquots of 100 microliters were injected automatically into the chromatograph. The separation of indomethacin was achieved on a reversed phase (C18, 10 micron) column with a mobile phase consisting of 65% (vol/vol) methanol in water solution of apparent pH 6.8 containing tetrabutylammonium hydrogensulfate as an ion pairing agent. Quantitation of indomethacin was performed by UV detection at 235 nm. At a 2.0 mg X l-1 concentration of indomethacin in plasma the analytical recovery was 82.9 +/- 3.4% (n = 7), the intra-day variability (CV) was 3.6% (n = 7) and the inter-day variability (CV) was 11.0% (n = 7). The calibration curve was linear (typical r-values greater than 0.990) in the range of plasma concentrations as usually found during indomethacin therapy (up to 6 mg X l-1). The limit of sensitivity is 0.025 mg X l-1. The metabolites O-desmethylindomethacin and O-desmethyldeschlorobenzoylindomethacin did not interfere with the method. The capacity of an analyst using this method with automated injection and peak integration is about forty samples in duplicate per day. The applicability of the method for pharmacokinetic studies is demonstrated.

Sensitive high-performance liquid chromatographic determination of indomethacin in human plasma. Pharmacokinetic studies after single oral dose

A sensitive high-performance liquid chromatographic assay for the specific determination of indomethacin at concentrations down to 20 ng/ml in human plasma is described. This method has been applied to investigate the disappearance of indomethacin from plasma of ten subjects following the intake of two formulations (Indocid and generic form). An initial half-life of 1.32 +/- 0.44 h-1 was found which is in good agreement with other findings, but the terminal phase was much longer (13.6 +/- 6.9 h-1) than previously reported. There is no difference between the two galenic forms (p less than 0.001).

High-performance liquid chromatographic assay of indomethacin and its application in pharmacokinetics in healthy volunteers

A new sensitive high-performance liquid chromatographic method for indomethacin from plasma on a reversed-phase column (C18) has been developed. The method involves precipitation of plasma with perchloric acid followed by diethyl ether extraction. The assay is quantitative down to 0.25 microgram ml-1 from a 200-microliters aliquot of plasma with a detection limit of 0.1 microgram ml-1 and a recovery of approximately 90%. The method was applied to single-dose studies with volunteers under various dietary restrictions. The results of these studies indicated that intrasubject variability within these regimens may be as important a factor as the intersubject variability already documented for this drug. These results have important implications in the determination of bioavailability and pharmacokinetic parameters of this drug.

High-pressure liquid chromatographic method with postcolumn, in-line hydrolysis and fluorometric detection for indomethacin in biological fluids

A rapid and sensitive method for the analysis of indomethacin in plasma and urine was developed using high-pressure liquid chromatography, postcolumn, in-line hydrolysis of indomethacin to a fluorophore, and detection of the fluorophore wih a fluorometer. The lower limit of detection was 1.5 ng/ml of plasma. The coefficient of variation at 30 ng/ml of plasma was 4.5% (n = 5). The nonconjugated metabolites of indomethacin, aspirin, and salicylate were resolved from indomethacin and the internal standard, alpha-methylindomethacin.