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  • Title: Theoretical relationship between the post-administration time and plasma or urinary concentration of a metabolite and the unchanged drug. Administration of caffeine to horses.
    Author: Aramaki S, Ishidaka O, Suzuki E, Momose A, Umemura K.
    Journal: Biol Pharm Bull; 1996 Oct; 19(10):1341-6. PubMed ID: 8913509.
    Abstract:
    In a doping test for racing horses, it is useful for the elucidation of the illegal use of drugs if one can estimate the time at which the detected drug was administered. In order to estimate the time which has elapsed after the administration of caffeine (CA) into horses, the ratios of concentration for the respective metabolites to the unchanged CA in the plasma or the urine were determined. These ratios have been known to be independent of the dose of CA. The relationship between [plasma or urinary concentration of a metabolite]/ [plasma or urinary concentration of the unchanged drug] and the post-administration time of CA was expressed in a theoretical equation using pharmacokinetic parameters. When CA was administered at 2.5 mg/kg intravenously, intramuscularly or orally, all of the experimentally observed values of plasma or urinary metabolites: theophylline, theobromine and paraxantine, agreed well with the theoretical formulas, indicating that there exists a theoretical relationship between the post-administration time and the concentration ratio of the respective metabolites to unchanged CA.
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