Contrast agents metabolites

Degradation of iopromide, a nonionic X-ray contrast agent, and its precursor aminotriiodoisophthalic acid were also assessed with T. versicolor. Rode and Muller [63] reported almost complete degradation (90%) of iopromide over 15 days and detected 14 metabolites from iopromide. From all the TPs, 5-methoxyacetylamino-... 

PET scans rely on radiopharmaceuticals as contrast agents, which can be used for imaging of tumor metabolism. The radioactive tracers are formed by labelling cell metabolites (for example, peptides, glucose, or nucleic acids) with positron-emitting isotopes ( C or (Fig. 1). Early diagnosis can be accomplished by observing radiopharmaceuticals that undertake metabolic processes associated with the diseases. 

MRI is much more sensitive to the phosphorus in ATP and other mobile metabolites than it is to the P atoms in bone. It is therefore particnlarly suitable for the study of soft tissues. Excellent pictures have been obtained of such organs as brain, heart and kidney. Whole-body scanning is now a practicable technique. Some P compounds can be used as contrast agents [70], for example, (12.142) (see 7.305). 

In contrast to these examples, the antibacterial agent piromidic acid (5.91, Fig. 5.24) is not converted to a lactam derivative but yields only the cw-ami-no acid derivative [188]. Steric features might underlie this metabolic difference. Bulky groups in close proximity to the N-atom seem to favor the formation of the amino acid metabolite, whereas substrates with an unhindered N-atom seem to favor the formation of a lactam metabolite. 

By contrast, when allopurinol riboside (11.19), a metabolite of allopuri-nol and an antiparasitic agent, is administered orally to humans, the drug is incompletely absorbed. The residual fraction is then extensively metabolized by the enteric flora to produce metabolites that are absorbed [41], Bacterial metabolism proceeds by cleavage to allopurinol, a reaction that apparently occurs only in the intestine. Although the examples described pertain to different animal species, it is clear that small structural changes can elicit major differences in metabolism. 

The term responsive (elsewhere indicated as smart ) refers to diagnostic agents whose contrasting properties are sensitive to a given physicochemical variable that characterizes the microenvironment in which the probe is distributed (116-117). Typical parameters of primary diagnostic relevance include pH, temperature, enzymatic activity, redox potential and the concentration of specific ions, and low-weight metabolites. 

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