Removal of Protein-Bound Uremic Toxins during Hemodialysis Using a Binding Competitor.

BACKGROUND AND OBJECTIVES: Current hemodialysis techniques fail to efficiently remove the protein-bound uremic toxins p-cresyl sulfate and indoxyl sulfate due to their high degree of albumin binding. Ibuprofen, which shares the same primary albumin binding site with p-cresyl sulfate and indoxyl sulfate, can be infused during hemodialysis to displace these toxins, thereby augmenting their removal. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We infused 800 mg ibuprofen into the arterial bloodline between minutes 21 and 40 of a conventional 4-hour high-flux hemodialysis treatment. We measured arterial, venous, and dialysate outlet concentrations of indoxyl sulfate, p-cresyl sulfate, tryptophan, ibuprofen, urea, and creatinine before, during, and after the ibuprofen infusion. We report clearances of p-cresyl sulfate and indoxyl sulfate before and during ibuprofen infusion and dialysate concentrations of protein-bound uremic toxins normalized to each patient's average preinfusion concentrations. RESULTS: We studied 18 patients on maintenance hemodialysis: age 36±11 years old, ten women, and mean vintage of 37±37 months. Compared with during the preinfusion period, the median (interquartile range) clearances of indoxyl sulfate and p-cresyl sulfate increased during ibuprofen infusion from 6.0 (6.5) to 20.2 (27.1) ml/min and from 4.4 (6.7) to 14.9 (27.1) ml/min (each P<0.001), respectively. Relative median (interquartile range) protein-bound uremic toxin dialysate outlet levels increased from preinfusion 1.0 (reference) to 2.4 (1.2) for indoxyl sulfate and to 2.4 (1.0) for p-cresyl sulfate (each P<0.001). Although median serum post- and predialyzer levels in the preinfusion period were similar, infusion led to a marked drop in serum postdialyzer levels for both indoxyl sulfate and p-cresyl sulfate (-1.0 and -0.3 mg/dl, respectively; each P<0.001). The removal of the nonprotein-bound solutes creatinine and urea was not increased by the ibuprofen infusion. CONCLUSIONS: Infusion of ibuprofen into the arterial bloodline during hemodialysis significantly increases the dialytic removal of indoxyl sulfate and p-cresyl sulfate and thereby, leads to greater reduction in their serum levels.

Enantioselective analysis of etodolac in human plasma by LC-MS/MS: Application to clinical pharmacokinetics.

Etodolac is a non-steroidal anti-inflammatory drug with preferential inhibition of cyclooxigenase-2 and is widely used in the management of pain in patients with inflammatory arthritis. Etodolac is available as a racemic mixture of (-)-(R)-Etodolac and (+)-(S)-Etodolac; cyclooxigenases inhibition is attributed to (+)-(S)-Etodolac. According to our knowledge, this is the first method for determination of etodolac enantiomers in plasma using LC-MS/MS. Plasma extraction were performed with 25µL of plasma and 1mL of n-hexane:ethyl acetate (95:5); racemic ibuprofen was used as internal standard. Resolution of enantiomers were performed in a Chiralcel(®)OD-H column; deprotonated [M-H](-) and their respective ion products were monitored at transitions of 286>242 for etodolac enantiomers and 205>161 for ibuprofen. The quantitation limit was 3.2ng/mL for both enantiomers in plasma. The method was applied to study the pharmacokinetics of etodolac enantiomers after the administration of a 300 and 400mg dose of racemic drug to a healthy volunteer. Analysis of plasma samples showed higher plasma concentration of (-)-(R)-Etodolacfor both doses (300mg dose: AUC(0-∞)49.80 versus 4.55ugh/mL;400mg dose: AUC(0-∞) 63.90 versus 6.00ugh/mL) with an (R)-(+)/(S)-(-) ratio of approximately 11.

Impact of inhalational exposure to ethanol fuel on the pharmacokinetics of verapamil, ibuprofen and fluoxetine as in vivo probe drugs for CYP3A, CYP2C and CYP2D in rats.

Occupational toxicology and clinical pharmacology integration will be useful to understand potential exposure-drug interaction and to shape risk assessment strategies in order to improve occupational health. The aim of the present study was to evaluate the effect of exposure to ethanol fuel on in vivo activities of cytochrome P450 (CYP) isoenzymes CYP3A, CYP2C and CYP2D by the oral administration of the probe drugs verapamil, ibuprofen and fluoxetine. Male Wistar rats exposed to filtered air or to 2000 ppm ethanol in a nose-only inhalation chamber during (6 h/day, 5 days/week, 6 weeks) received single oral doses of 10 mg/kg verapamil or 25 mg/kg ibuprofen or 10 mg/kg fluoxetine. The enantiomers of verapamil, norverapamil, ibuprofen and fluoxetine in plasma were analyzed by LC-MS/MS. The area under the curve plasma concentration versus time extrapolated to infinity (AUC(0-∞)) was calculated using the Gauss-Laguerre quadrature. Inhalation exposure to ethanol reduces the AUC of both verapamil (approximately 2.7 fold) and norverapamil enantiomers (>2.5 fold), reduces the AUC(0-∞) of (+)-(S)-IBU (approximately 2 fold) and inhibits preferentially the metabolism of (-)-(R)-FLU. In conclusion, inhalation exposure of ethanol at a concentration of 2 TLV-STEL (6 h/day for 6 weeks) induces CYP3A and CYP2C but inhibits CYP2D in rats.

Analysis of ibuprofen enantiomers in rat plasma by liquid chromatography with tandem mass spectrometry.

A sensitive and selective method for the analysis of ibuprofen enantiomers by LC-MS/MS was developed and validated for the purpose of application in pharmacokinetic studies in small experimental animals. Aliquots of 200 µL plasma were submitted to liquid-liquid extraction with hexane/diisopropylether (50:50 v/v) in acid pH. Separation was accomplished in a Chirex® 3005 (250 × 4.6 mm, 5 µm) column at 25°C with a mobile phase that consisted of 0.01 M ammonium acetate in methanol at a flow rate of 1.1 mL/min. The mass spectrometer consisted of an ESI interface operating at negative ionization mode and multiple reaction monitoring. The transitions 205 > 161 and 240 > 197 were monitored for ibuprofen enantiomers and fenoprofen (internal standard), respectively. Method validation included the evaluation of the matrix effect, stability, linearity, lower LOQ, within-run and between-run precision, and accuracy. The lower LOQ was 25 ng/mL for each ibuprofen enantiomer, and the calibration curves showed good linearity in the range 0.025-50 µg/mL. The method was successfully applied in the investigation of pharmacokinetic disposition of ibuprofen enantiomers in rats treated orally with 25 mg/kg of the racemate. Enantioselective kinetic disposition was observed with accumulation of (+)-(S)-ibuprofen in rats following single oral administration.

Effect of ibuprofen on bilirubin-albumin binding.

Ibuprofen is used for closing the ductus arteriosus in premature newborn infants. Ibuprofen interferes with bilirubin-albumin binding and increases the unbound bilirubin in pooled newborn plasma to levels similar to those produced by sulfisoxazole, a drug that causes kernicterus in premature newborn infants.

Enantioselective determination of ibuprofen in plasma by high-performance liquid chromatography-electrospray mass spectrometry.

The enantioselective analysis of ibuprofen (IBU), a chiral nonsteroidal anti-inflammatory drug, in human plasma was carried out by high-performance liquid chromatography (HPLC)-mass spectrometry (LC-MS-MS). The plasma samples were prepared by liquid-liquid extraction using hexane:ethyl acetate (8:2, v/v). The HPLC chiral resolution of IBU was obtained using a chiral stationary phase based on a tris-(3,5-dimethylphenylcarbamate) amylose derivative, under reversed phase conditions (CHIRALPAK AD-RH column), using a mobile phase consisting of methanol:water (8:2, v/v), containing 0.1% of an aqueous solution of phosphoric acid at pH 2, at a flow rate of 0.6 ml/min. A make-up liquid of 4.5% (w/v) NH(4)OH aqueous solution was used to assure optimum electrospray ionization in the negative mode. The coefficients of variation and deviation from nominal values were lower than 15% for both within- and between-day assays. The quantitation limit was 0.12 microg/ml and the linear range was 0.12-90.0 microg/ml for both enantiomers. The method proved to be suitable for single dose pharmacokinetic studies.

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.

The pharmacokinetics of ibuprofen suspension, chewable tablets, and tablets in children with cystic fibrosis.

OBJECTIVES: The objectives of this study were to compare the pharmacokinetic parameters of ibuprofen administered as a suspension, chewable tablet, or tablet in children with cystic fibrosis and to determine the optimal blood sampling times for measuring ibuprofen peak concentrations. STUDY DESIGN: A single oral 20 mg/kg dose of ibuprofen was administered, and blood samples were obtained at 15, 30, 45, 60, 120, 240, and 360 minutes after the dose was administered. Peak plasma concentration (Cmax ), time to peak concentration (Tmax ), and other pharmacokinetic parameters were determined and compared (analysis of variance and analysis of covariance). RESULTS: Thirty-eight children were included (22, 4, and 12 in the suspension, chewable tablet, and tablet groups, respectively). Tmax was the only parameter for which statistical differences were noted (suspension vs tablet, P

Effect of age on ibuprofen pharmacokinetics and antipyretic response.

The effect of age on ibuprofen pharmacokinetics and antipyretic effect was studied in 49 infants and children aged 3 months to 10.4 years. The relationship of plasma concentration to antipyretic effect was examined in 38 of the children by using an iterative least squares technique that allows estimation of drug concentration with time in a theoretical effect compartment and rate constant for elimination of drug from the effect compartment. There was a delay of 1 to 3 hours between peak ibuprofen plasma concentration and peak temperature decrement. The mean elimination rate constant from the effect compartment was 0.6 hour-1, corresponding to a half-life of drug in the effect compartment of 1.1 hours. The mean slope of the effect compartment concentration versus temperature regression line was -0.242 degrees C/mg per liter. Age did not significantly influence the rate of absorption of ibuprofen, its plasma concentration, its rate of elimination, or the time course of ibuprofen concentration in the effect compartment. However, in younger children the onset of antipyresis was earlier, maximum antipyretic effect was greater, and the area under the curve of the percentage of change in temperature from baseline versus time was greater than in older children. We conclude that the greater relative body surface area in younger children may allow more efficient dissipation of heat in response to antipyretic-induced lowering of the temperature "set point" in the hypothalamus.