Probenecid, sulfinpyrazone and pyrazinamide do not inhibit urinary excretion of the β₂‐adrenoceptor agonist clenbuterol in cattle

Abstract

The objective of this study was to develop an analytical approach to determine whether the illegal application of clenbuterol in cattle as an anabolic agent can be concealed by co‐treatment with substances that affect urinary excretion. Female veal calves were dosed orally with 0.8 μg clenbuterol per kg of body weight twice daily for 28 days, as licensed for the therapeutic use which is registered in most European countries. On the eighth day of clenbuterol treatment each calf was additionally dosed orally either with probenecid, sulfinpyrazone or pyrazinamide at three different doses that were increased in weekly intervals. During the treatment blood and urine samples were obtained and analysed for clenbuterol by enzyme immunoassay and by high performance liquid chromatography/ enzyme immunoassay to determine whether these drugs or their metabolites interfered with the immunological detection of clenbuterol. Clenbuterol could be detected in plasma (∼200 pg ml⁻¹) and urine (1–40 ng ml⁻¹) 5 h after the initial intake and throughout the whole treatment. None of the drugs reduced urinary excretion of clenbuterol to concentrations below the limit of detection. There was no prevention of clenbuterol detection in urine samples from calves that were co‐treated with the drugs tested in this study. Our results demonstrate the uselessness of applying these drugs in order to conceal the illegal use of clenbuterol in meat production.

Keywords:

• clenbuterol
• probenecid
• sulfinpyrazone
• pyrazinamide
• urinary excretion
• cattle
• HPLC
• enzyme immunoassay
• uricosurics

Notes

§To whom correspondence should be addressed at Institut für Physiologie, Forschungszentrum fur Milch und Lebensmittel Weihenstephan, Vöttinger Straße 45, D‐85350 Freising, Germany.