Urinary excretion of theobromine in horses given contaminated pelleted food

A high pressure liquid chromatographic (HPLC) method for measuring the theobromine content in cocoa husks, pelleted food and horse urine is described. Starting with 2 ml of urine, concentrations of 500 ng/ml could easily be detected. When feed containing 38.4 mg of theobromine was given twice daily to horses for 21/2 days, two days were needed after the last intake before the theobromine concentrations fell below the threshold value of 2 g/ml. The time at which the peak excretion rate occurred varied from 2 to 12 h after the last administration, while the excretion rate seemed to be dependent on the urinary flow. Theobromine could not be detected in plasma after administration in this way.