EXPERIMENTAL ADMINISTRATION OF 19-NORTESTOSTERONE AND DEXAMETHASONE IN CATTLE - ELIMINATION OF THE 2 DRUGS IN DIFFERENT BIOLOGICAL MATRICES

19-Nortestosterone (19-NT) is one of the mostly recurrent anabolic age nts on the black market of illicit drugs. Dexamethasone (DEXA) is lice nsed for therapy in veterinary practice but its misuse, although often suspected, has seldom been demonstrated. The excretion of 19-NT and D EXA is well documented when the compounds are administered independent ly but poor information is available in literature for instances when both drugs are administered as a mixture. To evaluate a radioimmunoass ay (RIA) for anabolic residues in urine, blood and faeces, the effect of the simultaneous administration and the subsequent elimination of t he two drugs, two animals were injected (4 times) with 19-NT and anoth er two (4 times) with 19-NT-DEXA. After preparation and a sequential c lean-up on C-18 and alumina columns, the samples were analysed by mean s of a specific 19-NT radioimmunoassay kit and an anti-DEXA antibody. Detection limits for both drugs were 0.5 ppb in blood samples and 2.0 ppb in urine and faecal samples. After the final treatment, positive 1 9-NT results were recorded at 14 and 21 d in urine and faecal samples, respectively. In the same matrices, positive DEXA values were found a t 11 and 28 d, respectively. Urinary excretion was the main metabolic path both for 19-NT and DEXA; only 30% of the residues were excreted v ia the faeces. The simultaneous injection of DEXA and 19-NT increased the urinary excretion of 19-NT; however, the excretion of 19-NT via fa ecal matter was similar for both groups.