Drug interaction in middle molecule analysis, with special reference to acetylsalicylic acid

Concerning the middle molecules in uremia and other diseases, the potential artifact that can impede an accurate quantitation of middle molecules and that is related to the absorption of a very commonly used drug, namely aspirin, is discussed. Peak 7c and peak b 4-2 are two different middle molecules separated by gel permeation chromatography followed by anion-exchange chromatography. Oral ingestion of acetylsalicylic acid modifies the chromatographic pattern of the middle molecule fraction in normal subjects and uremic patients. Peak 7c is increased in the urine of healthy subjects, whereas this is not the case for peak b 4-2: With the b 4-2 technique, ingestion of acetylsalicylic acid produces a higher peak b 5. This is consistent with the previous demonstration that peak 7c was eluted as peak b 5. Structural analogies between salicylate metabolites and orthohydroxyhippuric acid beta-glucuronate (i.e., the main component of peak 7c) could explain this drug-related artifact.