Quantitative determination of p-aminosalicylic acid and its degradation product m-aminophenol in pellets by ion-pair high-performance liquid chromatography applying the monolithic Chromolith Speedrod RP-18e column.

An ion-pair high performance liquid chromatographic method was developed for the simultaneous determination of p-aminosalicylic acid (PAS) and its degradation product m-aminophenol (MAP) in a newly developed multiparticular drug delivery system. Owing to the concentration differences of PAS and MAP, acetanilide and sulfanilic acid were used as internal standards, respectively. The separation was performed on a Chromolith SpeedROD RP-18e column, a new packing material consisting of monolithic rods of highly porous silica. The mobile phase composition was of 20 mm phosphate buffer, 20 mm tetrabutylammonium hydrogen sulphate and 16% (v/v) methanol adjusted to pH 6.8, at a flow-rate of 1.0 mL/min, resulting in a run-time of about 6 min. Detection was by UV at 233 nm. The method was validated and proved to be useful for stability testing of the new dosage form. Separation efficiency was compared between the new packing material Chromolith SpeedROD RP-18e and the conventional reversed-phase cartridge LiChroCART 125-4 (5 microm). A robustness test was carried out on both columns and different separation parameters (retention, resolution, run time, temperature) were determined.

Influence of acetylsalicylic acid and ketoprofen on canine thyroid function tests.

Many factors including drugs can influence thyroid function in humans, rats and dogs. Studies in humans report significant effects of non-steroidal anti-inflammatory agents (NSAIDs) on thyroid function tests, which can lead to misinterpretation of the results and inappropriate therapeutic decisions. As NSAIDs are used more and more frequently in dogs, it is important to know to what extent they can influence results. Eighteen spayed female beagle dogs were randomly assigned to three treatment sequences in a 3 x 3 crossover study design with treatments consisting of acetylsalicylic acid (ASA) (25 mg/kg BW q 12 h), ketoprofen (Keto) (1 mg/kg BW q 24 h) or placebo administered for a 1-week period with a 3-week washout period between treatment periods. Blood samples for determination of total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3), thyrotropin (TSH), reverse triiodothyronine (rT3), Keto and ASA concentrations were taken during each treatment period on days 0, 1, 3 and 7. During the washout period samples were taken weekly. A significant decrease in TT4 was observed as soon as 24 h after ASA administration, whereas the decrease in TT3 was less pronounced and differed significantly from the placebo only after 1 week of administration. No significant effects were found for free T4 and TSH with ASA administration. No significant effects on thyroid results were found following Keto administration. The results indicate that TT4 can be markedly decreased by ASA therapy and until the results of further studies are available, thyroid function test results should be interpreted cautiously in dogs on NSAIDs therapy.