Solid phase microextraction of diclofenac using molecularly imprinted polymer sorbent in hollow fiber combined with fiber optic-linear array spectrophotometry

A simple solid phase microextraction method based on molecularly imprinted polymer sorbent in the hollow fiber (MIP-HF-SPME) combined with fiber optic-linear array spectrophotometer has been applied for the extraction and determination of diclofenac in environmental and biological samples. The effects of different parameters such as pH, times of extraction, type and volume of the organic solvent, stirring rate and donor phase volume on the extraction efficiency of the diclofenac were investigated and optimized. Under the optimal conditions, the calibration graph was linear (r(2)=0.998) in the range of 3.0-85.0 μg L(-1) with a detection limit of 0.7 μg L(-1) for preconcentration of 25.0 mL of the sample and the relative standard deviation (n=6) less than 5%. This method was applied successfully for the extraction and determination of diclofenac in different matrices (water, urine and plasma) and accuracy was examined through the recovery experiments.

Spectrofluorometric determination of ketorolac tromethamine via its oxidation with cerium(IV) in pharmaceutical preparations and biological fluids

A simple and sensitive fluorometric method for determination of ketorolac tromethamine was studied. The method depends on oxidation of the drug with cerium(IV) and subsequent monitoring of the fluorescence of the induced cerium(III) at lambda(em) 365 nm after excitation at 255 nm. Different variables affecting the reaction conditions, such as the concentrations of cerium(IV), sulfuric acid concentration, reaction time, and temperature, were carefully studied and optimized. Under the optimum conditions, a linear relationship was found between the relative fluorescence intensity and the concentration of the investigated drug in the range of 0.1-0.8 microg/mL. No interferences could be observed from the excipients commonly present in dosage forms. The proposed method was successfully applied to the analysis of the investigated drug in its pure form, pharmaceutical preparations, and biological fluids with good accuracy and precision. The recoveries for pharmaceutical formulations ranged from 99.8-101.0 +/- 0.6% for tablets, 98.5-101.0 +/- 1.0% for ampoules, and 99.0-100.5 +/- 0.7% for eye drops. The results obtained by the proposed method were satisfactory compared with those obtained by the official method. The recoveries for biological fluids were 99.1-100.4 +/- 0.7 and 99.0-100.0 +/- 0.5% for plasma and urine, respectively.

The effects and metabolic fate of nitroflurbiprofen in healthy volunteers

OBJECTIVE

Nitric oxide-donating nonsteroidal anti-inflammatory drugs (NO-NSAIDs) are a new class of cyclooxygenase (COX) inhibitors. To investigate whether these drugs actually release nitric oxide (NO), we labeled the nitroxy group of nitroflurbiprofen with nitrogen 15 to determine the metabolic fate of this compound in humans.

METHOD

Six healthy volunteers who fasted were given an oral dose of 15 N-nitroflurbiprofen (100 mg). Samples of blood, urine, and gastric headspace gas were taken over a 24-hour period to determine the levels of nitroflurbiprofen, flurbiprofen, total nitrate/nitrite, 15 N-nitrate/nitrite, COX activity, and gastric NO. In a crossover study (1 week apart), a further 6 healthy volunteers who fasted were given an oral dose of nitroflurbiprofen (100 mg) or flurbiprofen (65 mg) and levels of gastric NO were determined.

RESULTS

Nitroflurbiprofen was undetectable in the systemic circulation. Levels of 15 N-nitrate/nitrite (5.2% +/- 1.5% enrichment) and flurbiprofen (2.4 +/- 0.7 microg/mL) peaked at 4 hours in the plasma and gradually decreased thereafter. In unstimulated blood, the plasma levels of thromboxane B 2 (COX-1 activity) were 2 to 3 ng/mL, and after calcium ionophore stimulation, large amounts of thromboxane B 2 were produced (112 +/- 31 ng/mL). Prostaglandin E 2 was undetectable in unstimulated blood. After lipopolysaccharide stimulation, the plasma levels of prostaglandin E 2 increased to 15 +/- 4 ng/mL. The metabolite flurbiprofen inhibited plasma COX-1 activity for the duration of the study period (maximum inhibition at 4 hours), whereas COX-2 activity recovered after 6 hours. In the crossover study, levels of gastric NO were higher in subjects given nitroflurbiprofen, when compared with those given flurbiprofen. (The area under the curve for gastric NO was 435 +/- 107 ppm . h versus 305 +/- 94 ppm . h [95% confidence interval of the difference, 89-172 ppm . h; P < .001]).

CONCLUSION

Nitroflurbiprofen was undetectable in the systemic circulation, suggesting metabolism to 15 N-nitrate/nitrite and flurbiprofen in the presystemic circulation. Levels of gastric NO were significantly higher after ingestion of nitroflurbiprofen than flurbiprofen.

Determination of valdecoxib and its metabolites in human urine by automated solid-phase extraction-liquid chromatography-tandem mass spectrometry

A simple, sensitive and specific automated SPE-LC-MS-MS assay was developed and validated for determination of valdecoxib (I), its hydroxylated metabolite (II) and carboxylic acid metabolite (III) in human urine. The analytes (I, II and III) and a structural analogue internal standard (I.S.) were extracted on a C(18) solid-phase extraction cartridge using a Zymark RapidTrace automation system. The chromatographic separation was performed on a narrow-bore reverse phase HPLC column with a mobile phase of acetonitrile-water (50:50, v/v) containing 10 mM 4-methylmorpholine (pH 6.0). The analytes were ionized using negative electrospray mass spectrometry, then detected by multiple reaction monitoring with a tandem mass spectrometer. The precursor to product ion transitions of m/z 313-->118, m/z 329-->196 and m/z 343-->196 were used to measure I, II and III, respectively. The assay exhibited a linear dynamic range of 1-200 ng/ml for I and II and 2-200 ng/ml for III in human urine. The lower limit of quantitation was 1 ng/ml for I and II and 2 ng/ml for III. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. Run time of 5.5 min for each sample made it possible to analyze a throughput of 70 human urine samples per run. The assay has been successfully used to analyze human urine samples to support clinical phase I and II studies.

Absorption, metabolism, and excretion of etoricoxib, a potent and selective cyclooxygenase-2 inhibitor, in healthy male volunteers

[(14)C]Etoricoxib (100 microCi/dose) was administered to six healthy male subjects (i.v., 25 mg; p.o., 100 mg). Following the i.v. dose, the plasma clearance was 57 ml/min, and the harmonic mean half-life was 24.8 h. Etoricoxib accounted for the majority of the radioactivity (approximately 75%) present in plasma following both i.v. and p.o. doses. The oral dose, administered as a solution in polyethylene glycol-400, was well absorbed (absolute bioavailability of approximately 83%). Total recovery of radioactivity in the excreta was 90% (i.v.) and 80% (p.o.), with 70% (i.v.) and 60% (p.o.) excreted in urine and 20% in feces after either route of administration. Radiochromatographic analysis of the excreta revealed that etoricoxib was metabolized extensively, and only a minor fraction of the dose (<1%) was excreted unchanged. Radiochromatograms of urine and feces showed that the 6'-carboxylic acid derivative of etoricoxib was the major metabolite observed (> or =65% of the total radioactivity). 6'-Hydroxymethyl-etoricoxib and etoricoxib-1'-N-oxide, as well as the O-beta-D-glucuronide conjugate and the 1'-N-oxide derivative of 6'-hydroxymethyl-etoricoxib, were present in the excreta also (individually, < or =10% of the total radioactivity). In healthy male subjects, therefore, etoricoxib is well absorbed, is metabolized extensively via oxidation (6'-methyl oxidation >1'-N-oxidation), and the metabolites are excreted largely in the urine.

Disposition of a specific cyclooxygenase-2 inhibitor, valdecoxib, in human

Valdecoxib is a potent and specific inhibitor of cyclooxygenase-2, which is used for the treatment of rheumatoid arthritis, osteoarthritis, and the dysmenorrhea pain. Eight male human subjects each received a single 50-mg oral dose of [(14)C]valdecoxib. Urine, feces, and blood samples were collected after administration of the radioactive dose. Most of the radioactivity in plasma was associated with valdecoxib and the hydroxylated metabolite of valdecoxib (M1). The estimated terminal half-life for valdecoxib was about 7 h. About 76.1% of the radioactive dose was recovered in urine and 18% of the radioactive dose was recovered in feces. Valdecoxib was extensively metabolized in human, and nine phase I metabolites were identified. The primary oxidative metabolic pathways of valdecoxib involved hydroxylation at either the methyl group to form M1 or N-hydroxylation at the sulfonamide moiety to form M2. Further oxidation of M1 led to the formation of several other phase I metabolites. Oxidative breakdown of the N-hydroxy sulfonamide function group in M2 led to the formation of corresponding sulfinic acid and sulfonic acid metabolites. The O-glucuronide conjugate of M1 and N-glucuronide conjugate of valdecoxib were the major urinary metabolites, which accounted for 23.3 and 19.5% of the total administered dose, respectively. The remaining urinary metabolites were glucuronide conjugates of other phase I metabolites. Only 3% of the administered dose was recovered in urine as unchanged parent, suggesting that renal clearance is insignificant for valdecoxib. Absorption of valdecoxib was excellent since the recovery of unchanged valdecoxib in feces was <1% of the administered dose.

The disposition and metabolism of rofecoxib, a potent and selective cyclooxygenase-2 inhibitor, in human subjects

The disposition and metabolism of rofecoxib, a selective cyclooxygenase-2 inhibitor, were examined in healthy human subjects and in cholecystectomy patients. After oral administration of [(14)C]rofecoxib (125 mg, 100 micro Ci) to healthy subjects, the mean concentrations of total radioactivity and rofecoxib in plasma as a function of time indicated that the t(max) was achieved at 9 h postdose. After t(max), levels of both radioactivity and rofecoxib decreased in a parallel, exponential fashion (effective t(1/2) approximately equal 17 h). A similar result was obtained after oral administration of [(14)C]rofecoxib (142 mg, 100 micro Ci) to cholecystectomy patients equipped with an L-tube. In healthy subjects, radioactivity was recovered predominantly from the urine (71.5% of dose), with a small amount excreted in feces (14.2%). In patients with an L-tube, half the radioactive dose was recovered in feces, with a lesser amount excreted in urine (28.8%) and a negligible fraction in bile (1.8%). Rofecoxib underwent extensive metabolism in humans, and very little parent drug was recovered unchanged in urine (<1%). Products resulting from both oxidative and reductive pathways were identified by a combination of (1)H NMR and liquid chromatography-tandem mass spectrometry analyses, and included rofecoxib-3',4'-trans-dihydrodiol, 4'-hydroxyrofecoxib-O-beta-D-glucuronide, diastereomeric 5-hydroxyrofecoxib-O-beta-D-glucuronide conjugates, 5-hydroxyrofecoxib, rofecoxib-erythro-3,4-dihydrohydroxy acid, and rofecoxib-threo-3,4-dihydrohydroxy acid. Interconversion of rofecoxib and 5-hydroxyrofecoxib appeared not to be a quantitatively important pathway of rofecoxib disposition in human subjects, in contrast to previous findings in rats.

High-throughput, semi-automated determination of a cyclooxygenase II inhibitor in human plasma and urine using solid-phase extraction in the 96-well format and high-performance liquid chromatography with post-column photochemical derivatization-fluorescence detection

Compound I, 5-chloro-3-(4-methanesulfonylphenyl)-6'-methyl-[2,3']bipyridinyl, has been found to be a specific inhibitor of the enzyme cyclooxygenase II (COX II). The anti-inflammatory properties of this compound are currently being investigated. HPLC assays for the determination of this analyte in human plasma and human urine have been developed. Isolation of I and the internal standard (II) was achieved by solid-phase extraction (SPE) in the 96-well format. A C8 SPE plate was used for the extraction of the drug from human plasma (recovery >90%) while a mixed-mode (C8/Cation) SPE plate was used to isolate the analytes from human urine (recovery approximately 71%). The analyte and internal standard were chromatographed on a Keystone Scientific Prism-RP guard column (20 x 4.6 mm) connected to a Prism-RP analytical column (150 x 4.6 mm), using a mobile phase consisting of 45% acetonitrile in 10 mM acetate buffer (pH = 4); the analytes eluted at retention times of 5.2 and 6.9 min for I and II, respectively. Compounds I and II were found to form highly fluorescent products after exposure to UV light (254 nm). Thus, the analytes were detected by fluorescence (lambda(ex) = 260 nm, lambda(em) =375 nm) following post-column photochemical derivatization. Eight point calibration curves over the concentration range of 5-500 ng/ml for human plasma and human urine yielded a linear response (R2>0.99) when a 1/y weighted linear regression model was employed. Based on the replicate analyses (n = 5) of spiked standards, the within-day precision for both assays was better than 7% C.V. at all points on the calibration curve; within-day accuracy was within 5% of nominal at all standard concentrations. The between-run precision and accuracy of the assays, as calculated from the results of the analysis of quality control samples, was better than 8% C.V. and within 8% of nominal. I was found to be stable in human plasma and urine for at least 8 and 2 months, respectively. In addition, the human plasma assay was semi-automated in order to improve sample throughput by utilizing a Packard liquid handling system and a Tom-Tec Quadra 96 SPE system. The precision and accuracy of the semi-automated procedure were comparable to the manual procedure. Over 5000 clinical samples have been analyzed successfully using these methods.

Stereoselective pharmacokinetics and inversion of (R)- ketoprofen in healthy volunteers

The pharmacokinetics of ketoprofen enantiomers were evaluated after 25-, 50-, and 100-mg doses of (R)- ketoprofen and 100 mg of racemic ketoprofen in 25 healthy volunteers (12 male and 13 female). The fractional inversion (Finv) of (R)- ketoprofen was 8.9 +/- 3.3% using plasma data and 10.0 +/- 2.2% using urine data. There were small (< 5%) but significant differences between the enantiomers for areas under the plasma concentration-time curve (AUC) after the racemic dose (P < 0.005). Half-lives were 130-144 minutes for (R)- ketoprofen and 132-209 minutes for (S)- ketoprofen. Dose proportionality in AUC and maximum plasma concentration (Cmax) values was noted for both enantiomers. A total of 69% of the dose was recovered in the urine as (R)- and (S)- ketoprofen and conjugates. The elimination rate constant of (R)- ketoprofen was significantly different (P < 0.05) between men and women. Exposure to cyclooxygenase inhibiting (S)- ketoprofen was approximately 10% of the dose after the administration of pure (R)- ketoprofen and was independent of gender.