We evaluated stable isotope analogues (SIAs) as internal standards in mass spectral drug assays on the analytic parameters of accuracy, precision, specificity, and limit of quantitation. Only one literature report suggests that the use of an SIA made an assay more accurate, although theoretic considerations strongly support their use. There is substantial evidence, however, that their use made assays more precise. Potentially, the chromatographic peak shape and retention time of the SIA can be compared with those of the analyte to support assay specificity, and this type of comparison has been implemented as a new computer program (QSIMPS). There is some evidence that SIAs can serve in "carrier" substances to increase recoveries and thus lower the limit of quantitation of an assay. However, the use of large amounts of an SIA (relative to the analyte) leads to analytic imprecision, because of memory effects, large blank values, and unacceptable confidence limits.

Applications to Analytic Chemistry: An Evaluation of Stable Isotopes in Mass Spectral Drug Assays

A computer program for the deconvolution of mass spectral peak abundance data from experiments using stable isotopes.

Detection and identification of carprofen and its in vivo metabolites in greyhound urine by capillary gas chromatography-mass spectrometry.

The significance of the adjacent cartilage in cartilage defect healing is not yet completely understood. Furthermore, it is unknown if the adjacent cartilage can somehow be influenced into responding after cartilage damage. The present study was undertaken to investigate whether the adjacent cartilage can be better sustained after microfracturing in a cartilage defect model in the stifle joint of sheep using a transcutaneous treatment concept (Vetdrop(®)). Carprofen and chito-oligosaccharids were added either as single components or as a mixture to a vehicle suspension consisting of a herbal carrier oil in a water-in-oil phase. This mixture was administered onto the skin with the aid of a specific applicator during 6 weeks in 28 sheep, allocated into 6 different groups, that underwent microfracturing surgery either on the left or the right medial femoral condyle. Two groups served as control and were either treated intravenously or sham treated with oxygen only. Sheep were sacrificed and their medial condyle histologically evaluated qualitatively and semi-quantitatively according to 4 different scoring systems (Mankin, ICRS, Little and O'Driscoll). The adjacent cartilage of animals of group 4 treated transcutaneously with vehicle, chito-oligosaccharids and carprofen had better histological scores compared to all the other groups (Mankin 3.3±0.8, ICRS 15.7±0.7, Little 9.0±1.4). Complete defect filling was absent from the transcutaneous treatment groups. The experiment suggests that the adjacent cartilage is susceptible to treatment and that the combination of vehicle, chitooligosaccharids and carprofen may sustain the adjacent cartilage during the recovery period.

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Transcutaneous treatment with vetdrop(®) sustains the adjacent cartilage in a microfracturing joint defect model in sheep.

The present preliminary study describes concentration time courses of the NSAID carprofen in the plasma and synovial fluid in a microfrature sheep model after transcutaneous treatments with a novel application device (Vetdrop®). To treat circumscribed inflammatory processes a transcutaneous application device could potentially be beneficial. After transcutaneous application normally lower systemic concentrations are measured which may reduce the incidence of side effects, whereas efficacy is still maintained. In this study carprofen was used based on its capacity to provide analgesia after orthopaedic procedures in sheep and it is considered that it may have a positive influence on the healing of cartilage in low concentrations. In all transcutaneously treated animals, carprofen plasma concentrations exceeded those of synovial fluid, although plasma levels remained significantly reduced (300-fold) as compared to carprofen administered intravenously. Furthermore, in contrast to the intravenously treated animals, a modest accumulation of carprofen in plasma and synovial fluid was observed in the transcutaneously treated animals over the 6-week treatment period. The transcutaneously administered carprofen using the Vetdrop® device penetrated the skin and both, plasma- and synovial concentrations could be measured repeatedly over time. This novel device may be considered a valuable transcutaneous drug delivery system.

/pdf/preliminary-study-on-carprofen-concentration-measurements-5408n935n9.pdf

Preliminary study on carprofen concentration measurements after transcutaneous treatment with Vetdrop® in a microfracture joint defect model in sheep

A gas chromatographic chemical ionization mass spectrometric assay has been developed to measure carprofen in blood. The method features the addition of either a structural or stable isotope analog internal standard to plasma prior to a simple benzene extraction at pH 4.5. The residue, after removal of the benzene, is methylated with ethereal diazomethane. Following evaporation of the methylating solvents, a portion of the reconstituted residue is analyzed by gas chromatography mass spectrometry. The mass spectrometer is set to monitor in the gas chromatographic effluent the [MH]+ ions of carprofen methyl ester and the methyl ester of the internal standard generated by isobutane chemical ionization. Assay sensitivity is 5 pmol ml-1. When 200 pmol ml-1 samples are analyzed using a stable isotope analog as the internal standard, the precision and accuracy are both 4%. Using a structural analog as the internal standard, the assay was neither as precise nor as accurate.

B. J. Hodshon

Papers

Determination of carprofen in blood by gas chromatography chemical ionization mass spectrometry.