Experimental administration of 19-nortestosterone and dexamethasone in cattle: elimination of the two drugs in different biological matrices

Abstract

19-Nortestosterone (19-NT) is one of the mostly recurrent anabolic agents on the black market of illicit drugs. Dexamethasone (DEXA) is licensed for therapy in veterinary practice but its misuse, although often suspected, has seldom been demonstrated. The excretion of 19-NT and DEXA is well documented when the compounds are administered independently but poor information is available in literature for instances when both drugs are administered as a mixture. To evaluate a radioimmunoassay (RIA) for anabolic residues in urine, blood and faeces, the effect of the simultaneous administration and the subsequent elimination of the two drugs, two animals were injected (4 times) with 19-NT and another two (4 times) with 19-NT–DEXA. After preparation and a sequential clean-up on C₁₈ and alumina columns, the samples were analysed by means 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 19-NT results were recorded at 14 and 21 d in urine and faecal samples, respectively. In the same matrices, positive DEXA values were found at 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 via the faeces. The simultaneous injection of DEXA and 19-NT increased the urinary excretion of 19-NT; however, the excretion of 19-NT via faecal matter was similar for both groups.