Studies on the metabolism of 2,4′-isobutylphenylpropionic acid (ibuprofen) by gas chromatography and mass spectrometry

Pharmacokinetic applications of capillary electrophoresis: A review on recent progress

This article covers recent publications from 2003 to 2005 on the subject of pharmacokinetic applications of CE. Many analytical methods were validated and more importantly, they were shown to have sufficient sensitivities to access pharmacokinetic data on different models. Because of unique advantages, such as simplified sample preparation methods, small sample amount required, high separation power, and speedy analysis, CE-based assays were found to gain popularity not only as a second method but also as a major method for many pharmacokinetic studies.

Determination of ibuprofen and tetrazepam in human urine by micellar electrokinetic capillary chromatography

A new micellar electrokinetic capillary chromatography method (MEKC) is proposed for the determination of ibuprofen and tetrazepam in human urine samples over a concentration range of therapeutic interest. A fused silica capillary (60 cm x 75 microm) is used. Ibuprofen and tetrazepam are detected via UV detection at 220 and 228 nm, respectively. Separation is performed at 25 degrees C and at a separation voltage of 30 kV, with 15 mM borate buffer (pH 10.2) containing 40 mM sodium dodecylsulfate as the electrolyte solution. Under these conditions the analytes were separated in <11 min. Sulfamethazine is used as an internal standard. Prior to determination, the samples are purified and enriched by means of an extraction-preconcentration step with a preconditioned C18 cartridge and by eluting the compounds with methanol. Good linearity, accuracy, precision, robustness and solution stability were achieved for the technique. Detection limits of 200 microg L(-1) for ibuprofen and 300 microg L(-1) for tetrazepam were obtained. These analytes were then determined in real urine using the technique.

Stereoselectivity of ibuprofen metabolism and pharmacokinetics following the administration of the racemate to healthy volunteers

1. The stereoselective metabolism and pharmacokinetics of the enantiomers of ibuprofen have been investigated following the oral administration of the racemic drug (400 mg) to 12 healthy volunteers.2. The stereochemical composition of the drug in serum, both total and unbound, and drug and metabolites, both free and conjugated, in urine were determined by a combination of the direct and indirect chromatographic procedures to enantiomeric analysis. 3. The oral clearance of (S)-ibuprofen was significantly greater than that of the R-enantiomer (74.5 +/- 18.1 versus 57.1 +/- 11.7 ml min(-1); p < 0.05) and the clearance of (R)-ibuprofen via inversion was ca two fold that via alternative pathways. 4. Some 74.0 +/- 9.6% of the dose was recovered in urine over 24 h as ibuprofen, 2-hydroxyibuprofen and carboxyibuprofen, both free and conjugated with glucuronic acid. Analysis of the stereochemical composition of the urinary excretion products indicated that 68% of the dose of (R)-ibuprofen had undergone chiral inversion. 5. Metabolism via glucuronidation and both routes of oxidation, showed enantio-selectivity for (S)-ibuprofen, the enantiomeric ratios (S/R) in partial metabolic clearance being 7.1, 4.8 and 3.4 for formation of ibuprofen glucuronide, 2-hydroxyibuprofen and carboxyibuprofen respectively.6. Modest stereoselectivity was observed in the formation of (2'R, 2R)- and (2'S, 2S)-carboxyibuprofen in comparison to the alternative diastereoisomers, the ratios in formation clearance being 1.6 and 1.2 respectively.

Enantioselective analysis of ibuprofen in human plasma by anionic cyclodextrin-modified electrokinetic chromatography

This paper reports the development of a rapid method for the enantioselective analysis of the nonsteroidal anti-inflammatory drug ibuprofen in human plasma by capillary electrophoresis employing the anionic cyclodextrin-modified electrokinetic chromatography mode. Sample cleanup was carried out by acidification with HCl followed by liquid-liquid extraction with hexane:isopropanol (99:1 v/v). The complete enantioselective analysis was performed within 10 min, using 100 mmol L(-1) phosphoric acid/triethanolamine buffer, pH 2.6, containing 2.0% w/v sulfated beta-cyclodextrin as chiral selector; fenoprofen, another nonsteroidal anti-inflammatory drug, was used as internal standard. The calibration curves were linear over the concentration range of 0.25-125.0 microg mL(-1) for each enantiomer of ibuprofen. The mean recoveries for ibuprofen enantiomers were up to 85%. The enantiomers studied could be quantified at three different concentrations (0.5, 5.0 and 50.0 microg mL(-1)) with a coefficient of variation and relative error not higher than 15%. The quantitation limit was 0.2 microg mL(-1) for (+)-(S)- and (-)-(R)-ibuprofen using 1 mL of human plasma. The plasma endogenous compounds and other drugs did not interfere with the present assay. The analysis of real plasma samples obtained from a healthy volunteer after administration of 600 mg of racemic ibuprofen showed a maximum plasma level of 29.6 and 39.9 microg mL(-1) of (-)-(R)- and (+)-(S)-ibuprofen, respectively, and the area under plasma concentration-time curve AUC(0-infinity) (+)-(S)/AUC(0-infinity) (-)-(R) ratio was 1.87.

Polymeric drugs derived from ibuprofen with improved antiinflammatory profile

A new methacrylic monomeric compound bearing Ibuprofen (MIA) and the respective polymethacrylic macromolecular derivative (polyMIA) were evaluated for antiinflammatory properties in order to study their pharmacological activity profile. The macromolecular drug is constituted of Ibuprofen residues linked covalently to a polymethacrylic support, as a side substituent of the repeating unit, by means of a spacer group (p-aminophenoxy) that, in addition, is the most representative metabolite of Paracetamol. The Ibuprofen is slowly released from the polymeric support by hydrolysis of the ester bond in a biological medium. Different antiinflammatory testing methods were used; and the results obtained indicate that the monomeric and polymeric forms display higher potency to inhibit acute inflammatory processes than the traditional Ibuprofen form, even doubling the power of Ibuprofen. In addition, they present higher activity against chronic experimental processes, as well as an excellent antinociceptive behavior to inhibit the pain associated with arthritic diseases. According to previous reports and results presented in this article, we can conclude that the new polymethacrylic structures show higher analgesic, antipiretic, and antiinflammatory activities due to the possible activity of the macromolecular drug as well as to the controlled Ibuprofen release from the macromolecular delivery system. After releasing of the side active residue, a derivate of poly(sodium methacrylate) is formed, which is cleared from the body easily by the normal pathway of kidney metabolism.

Metabolism of isobutylnaphthyl acetic acid in rats: determination of the chemical structures of metabolites

After oral and intravenous administration of radiolabelled isobutylnaphthyl acetic acid (INAA) to rats two metabolites were isolated from urine and plasma by HPLC. Field desorption, high resolution electron impact mass spectrometry as well as GC-MS after derivatization were used for structure elucidation and identification of the metabolites. The main biotransformation product in rat urine was found to be 5-(2'-hydroxy-2'-methyl-propyl)-1-naphthyl acetic acid (M1). The main metabolite in plasma was derived and was found to be 5-(2'-carboxypropyl)-1-naphthyl acetic acid (M2).

Determination of ibuprofen and its major metabolites in human urine by high-performance liquid chromatography

A sensitive and selective high-performance liquid chromatographic assay for free and total ibuprofen and its major metabolites in human urine is described. Urine is acidified, drug and metabolites are extracted into hexane-propanol, back-extracted into sodium bicarbonate, neutralized and chromatographed. Ibufenac (4-isobutylphenylacetic acid) and 2-phenylpropionic acid were employed as internal standards. The extraction efficiencies were 94-100% for all compounds. The two metabolites and their internal standard were separated using an isocratic chromatographic system, followed by an abrupt step gradient to a second eluent for separation of ibuprofen and its internal standard with a total run time of 18 min. Detection was by a fixed-wavelength detector (214 nm). Sample-to-sample and day-to-day reproducibility studies yielded coefficients of variability of less than 9% for all compounds. The sensitivity was sufficient to determine 2.5 micrograms/ml free ibuprofen in 100 microliters urine.

The influence of hemodialysis on the pharmacokinetics of ibuprofen and its major metabolites

The pharmacokinetics of ibuprofen and its two major metabolites, the hydroxy and carboxy derivatives, were studied in seven functionally anephric subjects undergoing hemodialysis therapy. Subjects received ibuprofen 800 mg tid for 14 days. Hemodialysis was performed three times weekly during this period. Arterial and venous blood samples were collected before dialysis and along with dialysate, and during the final dosing interval and dialysis session. No accumulation of ibuprofen plasma concentrations and an absence of intact ibuprofen in dialysate indicated clearance through metabolic pathways. The metabolites did accumulate significantly (mean plasma levels, carboxy 249 micrograms/mL and hydroxy 57 mu/mL); however, both were detected in dialysate. Mean extraction efficiencies were 0.16 (hydroxy) and 0.15 (carboxy). Dialysis clearance calculated by arterial-venous difference was found to agree with actual recovery in dialysate for both metabolites. Side effects were not observed in any subject.

Determination of ibuprofen in human plasma by solid phase extraction and reversed-phase high-performance liquid chromatography

A new, sensitive and simple method for the rapid quantitative determination of ibuprofen in human plasma has been developed. This method involves the use of a solid phase extraction on "Baker" C-18 disposable extraction columns for sample clean-up and uses mefenamic acid as an internal standard. Separation and quantitation are performed by reversed-phase liquid chromatography using a Nucleosil C18 column and methanol-0.04 M phosphoric acid (80:20, v/v), as the mobile phase. Detection was achieved by UV-absorbance measurements at 229 nm.

Determination of ibuprofen in serum by high-performance liquid chromatography and application to ibuprofen disposition

A high-performance liquid chromatographic method for quantitation of ibuprofen from serum and application of this method to ibuprofen disposition in the dog is described. The drug was extracted from acidified plasma with dichloromethane. The internal standard used was a methanolic solution of 4-n-butylphenylacetic acid. A muBondapak C18 column was used for analysis; this mobile phase was methanol-water-glacial acetic acid (pH 3.4) (75 : 24 : 1, v/v). A wavelength of 272 nm was used to monitor ibuprofen and the internal standard. Method sensitivity was 0.5 microgram/ml serum using either 0.5 or 1.0 ml of sample, and no interference was found from endogenous compounds or other commonly used anti-inflammatory agents. The coefficients of variation of the method were 4.2% and 6.0% for sample containing 50.0 and 6.25 microgram/ml of ibuprofen, respectively, and the calibration curve was linear for the range of 0.5 to 100 microgram/ml. This method was demonstrated to be suitable for pharmacokinetic and/or biopharmaceutical studies of ibuprofen in man and the dog.

Urinary metabolites of 2-ethyl-2-methylsuccinimide (ethosuximide) studied by combined gas chromatography mass spectrometry

Metabolites of 2-ethyl-2-methylsuccinimide (ethosuximide) have been studied by combined gas chromatography mass spectrometry in a urine sample from a patient treated for petit mal epilepsy with ethosuximide. A new metabolite, 2-carboxymethyl-2-methylsuccinimide, was identified in the urine. It is presumably formed by omega 1-hydroxylation of the ethyl sidechain of the drug followed by a further oxidation of the primary alcohol to a carboxyl group. A previously identified metabolite, 2-ethyl-3-hydroxy-2-methylsuccinimide, was shown in the present study to yield two gas chromatographic peaks (as the N-methylated compound), indicating the existence of a diastereoisomeric pair. Thus, the enzyme responsible for the ring hydroxylation is probably not stereospecific, or alternatively two enzymes with different stereospecificity may exist.