Study of dexamethasone urinary excretion profile in cattle by LC-MS/MS: comparison between therapeutic and growth-promoting administration.

Dexamethasone is a potent synthetic corticosteroid widely employed as a therapeutic agent in cattle. Besides this legal use, corticosteroids are also administered at low dosages as growth-promoters either alone or in combination with other steroids or with beta-agonists. For this reason, appropriate control plans are established to survey corticosteroid misuse, using liver or urine as biological matrices. Since few data are available about the kinetics of dexamethasone excretion in meat cattle, an experimental study was designed to assess the drug residue levels in urines following either a therapeutic (60 microg of dexamethasone sodium phosphate/kg b.w., for three consecutive days) or a growth-promoting schedule (0.7 or 1.4 mg of dexamethasone sodium phosphate per capita/day for 60 days). The urinary elimination of dexamethasone, which was predominantly excreted in the unmodified form, was determined by high-performance liquid chromatography/tandem mass spectrometry at different time intervals, i.e. during the treatments and after appropriate withdrawal times. Our findings confirm the high and rapid rate of dexamethasone urinary excretion irrespective of the nature of the treatment, and provide useful reference values that can be conveniently employed for forensic purposes.