Stability of 5-aminosalicylic acid and its metabolites in plasma at -20 degrees C. Formation of N-beta-D-glucopyranosyl-5-aminosalicylic acid.

The stability of 5-aminosalicylic acid and its metabolites has been investigated when stored frozen. N-beta-D-Glucopyranosyl-5-aminosalicylic acid was formed in considerable amounts concomitant with a decrease in 5-aminosalicylic acid in plasma samples spiked with 5-aminosalicylic acid as well as in standard solutions of 5-aminosalicylic acid buffered with potassium phosphate between pH 5.5 and pH 8.0 with 4.0 mM glucose added and stored at -20 degrees C. Thus N-beta-D-glucopyranosyl-5-aminosalicylic acid might not, as previously described, be a metabolite of 5-aminosalicylic acid but an artifact formed during storage of plasma samples. The N-glucoside formed could be quantitatively degraded to 5-aminosalicylic acid and glucose by adding 0.2 M potassium phosphate buffer pH 3.0 to the sample prior to the analysis. The metabolites of 5-aminosalicylic acid (N-formyl-5-aminosalicylic acid, N-acetyl-5-aminosalicylic acid and N-butyryl-5-aminosalicylic acid) were found to be stable in plasma stored at -20 degrees C for at least eight months.