Stereospecific assay and stereospecific disposition of racemic carprofen in rats.

A procedure was developed for the separation and selective quantitative determination of the (S)(+)- and (R)(-)-enantiomers of the racemic anti-inflammatory drug carprofen as their diastereomeric l-(-)-alpha-methylbenzylamides. These derivatives are obtained in equivalent yields by reacint purified 14C-carprofen from biological specimens with l-(-)-alpha-methylbenzylamine via the 1,1'-carbonyldiimidazole intermediate, followed by extraction and differential radiometric quantitation of the TLC-separated diastereomers. In the rat, the (R)(-)-carprofen enantiomer was eliminated from blood and secreted in the bile as the ester glucuronide at a rate approximately twice that of the (S)-(+)-enantiomer, resulting in the accumulation of the pharmacologically more active (S)(+)-enantiomer in the rat blood. Evidence for an additional process favoring the elimination of the (R)(-)-enantiomer in the rat was derived from pharmacokinetic data evaluation.

Spectrofluorometric determination of substituted tetrahydrocarbazoles by a methylene blue sensitized photolytic reaction.

A spectrofluorometric method was developed for the determination of 6-chloro-9-[2-(2-methyl-5-pyridyl)ethyl]-1,2,3,4-tetrahydrocarbazole-2-methanol hydrochloride and its carboxylic acid analog in blood and urine. It involves extraction of both compounds at neutral pH, either from blood into ethyl acetate (the residue of which is dissolved in either) or from urine directly into ether. Both the alcohol and the acid are separated from each other by selective extraction into acid or base, respectively, and then reextracted into either from the respective aqueous medium by appropriate pH adjustment. The residues of the ether extracts containing the compounds are dissolved separately in 0.25 N NH4OH. Methylene blue is added to all samples, which are then exposed to UV energy for 15 min to produce the fluorophores. The fluorescence of the solutions is read at 370 nm, with excitation at 340 nm. The linear range of quantitation of both compounds is 0.02-10 mug/each/ml of final solution. The method was applied to the determination of blood levels and urinary excretion of the alcohol and its acid metabolite in a dog.

Metabolism of carprofen, a nonsteroid anti-inflammatory agent, in rats, dogs, and humans.

The metabolic disposition of 14C-labeled carprofen [(+/-)-6-chloro-alpha-methylcarbazole-2-acetic acid] was investigated in rats, dogs, and humans. Carprofen is eliminated predominantly by biotransformation in these three species. In dogs and rats, the direct conjugation of carprofen to form an ester glucuronide and oxidation to the C-7 and the C-8 phenols followed by their conjugation represent the major metabolic pathways. Small amounts of the alpha-hydroxy derivative also are formed by these species and are excreted free in the urine. In dogs, biliary secretion predominates, and 70% of an intravenous dose of carprofen is excreted in the feces while 8--15% of the dose is excreted in the urine. In rats, fecal excretion due to biliary secretion varies from 60 to 75%, and urinary excretion accounts for 20--30% of an intravenous dose. In humans direct conjugation of carprofen represents the only significant pathway of metabolism. Between 65 and 70% of the orally administered carprofen was found to be excreted as the ester glucuronide in the urine, and most of the remaining dose was estimated to be secreted as this metabolite in the bile. Due to enterohepatic circulation, only a fraction of the biliary metabolite was recovered in the feces in humans. Less than 5% of the dose was excreted in human urine as free, intact carprofen. In dogs and humans, plasma levels of carprofen and of total radioactivity exhibit a multiphasic decline. In the three human subjects studied, the terminal component declined with a 13--26 hr half-life; the terminal half-life was approximately 40 hr in dogs.