Method for extraction and separation of drugs and metabolites from biological tissue

Pharmacokinetic study of the hepatobiliary transport of indomethacin

PURPOSE

The biliary excreted amount of indomethacin and its glucuronide is related to the intestinal toxicity of this drug. In the present study, we investigated the hepatobiliary transport of indomethacin.

METHODS

The uptake of indomethacin into primary cultured rat hepatocytes and COS-7 cells transfected with cDNA encoding sodium taurocholate co-transporting polypeptide or organic anion transporting polypeptide 1 was examined. Moreover, we compared the biliary excretion of indomethacin and its glucuronide between Sprague-Dawley (SD) rats and Eisai hyperbilirubinemic rats (EHBR) whose canalicular multispecific organic anion transporter/multidrug resistance associated protein 2 (cMOAT/MRP2) function is hereditarily defective.

RESULTS

The uptake of indomethacin into rat hepatocytes was mediated by Na+-dependent and independent active transport systems. Neither transfectant stimulated the uptake of indomethacin. After intravenous infusion of indomethacin to SD rats, the biliary excretion of indomethacin glucuronide exceeded that of indomethacin. The indomethacin transport clearance across the bile canalicular membrane was comparable between SD rats and EHBR, whereas the corresponding value for indomethacin glucuronide in EHBR was approximately 50% that in SD rats.

CONCLUSIONS

These results indicate that another transporter(s) is involved in the hepatic uptake of indomethacin and the canalicular transport of indomethacin glucuronide is mediated by cMOAT/MRP2 whereas that of indomethacin is not mediated by cMOAT/MRP2.

Pharmacokinetics of indomethacin in sheep after intravenous and intramuscular administration

The pharmacokinetics of indomethacin (1 mg/kg) was determined in six adult sheep after intravenous (i.v.) and intramuscular (i.m.) injection. Plasma concentrations were maintained within the therapeutic range (0.3-3.0 microg/mL) from 5 to 50 min after i.v. and from 5 to 60-90 min after i.m. administration. After two trials, indomethacin best fitted an open two-compartment model. The mean (+/- SD) volumes of distribution at steady state (Vd(ss)) were 4.10 +/- 1.40 and 4.21 +/- 1.93 L/kg and the mean clearance values (ClB) were 0.17 +/- 0.06 and 0.22 +/- 0.12 L/h x kg for i.v. and i.m. routes, respectively. The elimination phase half-lives did not show any significant difference between routes of injection (t1/2beta = 17.4 +/- 4.6 and 21.25 +/- 4.44 h, i.v. and i.m. respectively). After i.m. administration, plasma maximum concentration (Cmax = 1.10 +/- 0.68 microg/mL) was reached 10 min after dosing; the absorption phase was fast (Kab = 26 +/- 18 h(-1)) and short (t1/2ab = 2.33 +/- 1.51 min) and the mean bioavailability was 91.0 +/- 32.8%, although there was considerable interanimal variation. In some individuals, bioavailability was higher than 100%. This fact combined with the slower elimination phase after i.m. than after i.v. administration, could be related with enterohepatic recycling.

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 method for the determination of indomethacin and its two primary metabolites in urine

Quantitation of total amounts (i.e., free compound plus glucuronide conjugate) of indomethacin (INDO) and its deschlorobenzoyl (DBI) and desmethyl (DMI) metabolites in human urine is described. An aliquot (0.4 ml) of urine is incubated with glucuronidase (1000 U, 2 h, 37 degrees C) and extracted with 5 ml of dichloromethane containing the internal standards: the fluoro analogue of INDO, F-INDO, and indole-3-propionic acid (IPA). The organic phase is concentrated, dissolved in mobile phase and aliquots are injected onto the high-performance liquid chromatograph. INDO and DMI are measured with UV detection at 254 nm over a linear range of 0.25-125 micrograms/ml. Retention times for DMI, F-INDO and INDO are 4.0, 6.8 and 12.1 min, respectively, using a C8 reversed-phase column with an acetonitrile-0.1 M acetate, pH 5.0 (30:70) mobile phase at a 2.5 ml/min flow-rate. DBI is measured using fluorescence detection (excitation = 305 nm, emission = 370 nm) over a linear range of 0.25-12.5 micrograms/ml. Retention times for DBI and IPA are 4.5 and 7.8 min, respectively, on the same C8 column with an acetonitrile-0.025 M acetate, pH 4.0 (22:78) mobile phase at a 2.0 ml/min flow-rate. Inter- and intra-day precision were smaller than 10% for INDO, DMI and DBI over the concentration ranges indicated.

Bio-distribution in rats of some salicylates with low gastric ulcerogenicity

The distribution of three radioactively labelled salicylate derivatives with low ulcerogenic activity was compared with that of acetylsalicylic acid (ASA) and salicylic acid using whole body autoradiography and liquid scintillation counting techniques in rats. The methyl ester of ASA (AME) was distributed in vivo very similarly to that observed with ASA and salicylic acid. AME is rapidly demethylated following absorption from the stomach and is subsequently converted to ASA and salicylate. Salicylate is the main metabolite produced from both AME and ASA, which specifically accumulates in inflamed tissues. The 3-methyl- and 6-methyl-substituted salicylic acids are not as rapidly absorbed as either ASA or salicylic acid and do not pass readily into the brain or bone marrow. These results show that the methyl (ester) group of AME (which adequately protects the gastric mucosa from damage caused by ASA itself) does not impair the quantity of pharmacologically active form of drug (salicylate and ASA) generated in vivo. However, insertion of the methyl group at the 3- and 6-position of salicylic acid markedly affects both absorption, distribution and pharmaco-activity of these acids.

Rapid determination of indomethacin and salicylic acid in serum by means of reversed-phase liquid chromatography

A method for the quantitative analysis of indomethacin and salicylic acid in blood serum and urine by high-performance liquid chromatography is described. A C18-bonded silica was used as the stationary phase and mixtures of ethanol, n-butanol and aqueous buffer as the mobile phase. Before injection the serum is deproteinized and extracted in one step. The recovery of the extraction was found to be 88% and 77% for indomethacin and salicylic acid, respectively. The relative standard deviations of the analysis for 0.5 micrograms indomethacin and 5 micrograms salicyclic acid per ml serum were 3.6% and 3.2%, respectively. The detection limits for indomethacin and salicylic acid were 2 ng. This corresponds for both substances to 0.1 micrograms/ml serum for an injection volume of 100 microliters. The method enables simultaneous determination of possibly formed metabolites. A number of concurrently administered drugs do not interfere with the analysis. The interactive effects of co-medication of indomethacin and salicylic acid on the serum concentration of indomethacin is demonstrated by measuring the pharmacokinetic curves.

Determination of indomethacin in serum by an extractive alkylation technique and gas-liquid chromatography

A method for determining indomethacin in serum has been developed, involving extractive alkylation, in which indomethacin is converted into its ethyl ester, and subsequent gas chromatographic determination of the ester. The method is specific and permits the determination of amounts down to 50 ng/ml in serum. The indomethacin concentration in serum was followed for 24 h after oral and rectal application and the results are compared with those reported in the literature.

Three alkylation methods for the determination of indometacin in plasma by electron capture gas chromatography

The following alkylation methods for the determination of indometacin in plasma by electron capture gas chromatography are compared: 1, alkylation with diazopropane; 2, extractive alkylation; 3, alkylation by a solid-liquid phase transfer catalysed process. The drug in plasma at pH 4.0 is initially extracted with heptane containing 5% n-pentanol. The methyl ester of indometacin is based as internal standard. After alkylation to the propyl ester according to one of the three alkylation methods, indometacin can be determined down to 5 ng per sample by electron capture gas chromatography. The relative standard deviations (n = 10) at the 200 ng level are 5.1% for the alkylation with diazopropane, 7.5% for the extractive alkylation technique and 3.5% for the alkylation by the solid-liquid phase transfer catalysed process. The comparatively low value obtained by the last method indicates that decomposition of indometacin can be avoided under such mild conditions.

Determination of indomethacin in serum and urine by electron-capture gas-liquid chromatography

A specific and sensitive method for the quantitative determination of indomethacin in serum and urine is described. The drug is extracted at pH 5.0 with 1,2-dichloroethane and a portion of the organic extract is concentrated and made to react with diazoethane in diethyl ether. The ethyl ester derivative is analyzed by electron-capture gas-liquid chromatography, quantitation being achieved by comparison of peak areas for samples and standards, which are prepared in serum or urine and treated in the same manner as the samples. The limit of sensitivity is 50 ng/ml and the relative standard derivation for repeat determinations on the same sample is about 3%.

The effects of salicylate on the activity of rat liver tryptophan pyrrolase in vitro and in vivo

1. Salicylate, in concentrations of 0.05mm and above, inhibits the basal activity of tryptophan pyrrolase in homogenates of rat liver and the activity induced by cortisol but not that induced by tryptophan. The inhibition is abolished by adding haematin to the reaction mixtures. 2. The intraperitoneal injection of 400mg of sodium salicylate/kg in the rat causes a decrease in the tryptophan pyrrolase activity in the liver at 30min, the activity is restored to normal at 2h, increases to sixfold after 5h and returns to the basal value at 12h. The activation of the enzyme by salicylate is prevented by the administration of cycloheximide but not by pretreatment with actinomycin D. The effects of the combined injection of salicylate and cortisol are additive, whereas those of salicylate plus tryptophan are not. The injection of salicylate causes a progressive increase in the holo-/apo-enzyme ratio and an increased content of tryptophan in the liver over a period of 3h. 3. It is suggested that salicylate inhibits tryptophan pyrrolase activity in vitro and in vivo by interacting with iron protoporphyrins and causes a later enhancement of the enzyme activity in vivo by a mechanism involving the release of tryptophan from its binding sites on circulating albumin and on other proteins.