e2.1.3 Pharmacokinetics in humans
In a study to define the pharmacological response of humans to ractopamine, the pharmacokinetics of ractopamine were determined in six healthy male human volunteers
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發表於 2012-3-5 08:14
In a study to define the pharmacological response of humans to ractopamine, the pharmacokinetics of ractopamine were determined in six healthy male human volunteers given a single oral dose of 40 mg of ractopamine hydrochloride. Blood plasma and urine samples were collected 24 after dosing and analysed by high-performance liquid chromatography (HPLC) with electrochemical detection. Ractopamine was rapidly absorbed, with the mean peak plasma concentration of 41.2 ng/ml occurring after an average of 0.6 h. The mean half-life was 3.94 h. Ractopamine was no longer detected in plasma 24 h after dosing, except at very low concentrations in one volunteer. Only about 2% of the total administered dose was excreted in the urine as unchanged ractopamine by 24 after dosing. After treatment of urine samples with beta-glucuronidase and sulfatase for hydrolysis of ractopamine conjugates, urine excreted 0-24 h after dosing contained an average of 45.7% of the administered dose as free ractopamine, indicating that <5% of total ractopamine excreted represented the parent drug. The urinary metabolites were monoglucuronide and monosulfate conjugates, with ractopamine monosulfate being the major metabolite present. Of the total administered dose that was excreted in the urine, about 72% was excreted within 6 h after dosing. The results confirmed that ractopamine was extensively and rapidly absorbed, with an oral bioavailability of a minimum of 45.7% of the administered dose. Owing to rapid metabolism, the orally administered dose of 40mg produced low systemic concentrations of parent ractopamine, suggesting significant first-pass metabolism of the drug. The available data strongly suggest that disposition, metabolism, and excretion of ractopamine in humans are consistent with the pharmacokinetics and biotransformation observed in animals and for other phenolic, catecholic, and resorcinolic phenethanolamine beta-adrenergic agents (Hunt, 1994; Smith & Rodewald, 1994; Smith, 1998).
In a study to define the pharmacological response of humans to ractopamine, the pharmacokinetics of ractopamine were determined in six healthy male human volunteers given a single oral dose of 40 mg of ractopamine hydrochloride. Blood plasma and urine samples were collected 24 after dosing and analysed by high-performance liquid chromatography (HPLC) with electrochemical detection. Ractopamine was rapidly absorbed, with the mean peak plasma concentration of 41.2 ng/ml occurring after an average of 0.6 h. The mean half-life was 3.94 h. Ractopamine was no longer detected in plasma 24 h after dosing, except at very low concentrations in one volunteer. Only about 2% of the total administered dose was excreted in the urine as unchanged ractopamine by 24 after dosing. After treatment of urine samples with beta-glucuronidase and sulfatase for hydrolysis of ractopamine conjugates, urine excreted 0-24 h after dosing contained an average of 45.7% of the administered dose as free ractopamine, indicating that <5% of total ractopamine excreted represented the parent drug. The urinary metabolites were monoglucuronide and monosulfate conjugates, with ractopamine monosulfate being the major metabolite present. Of the total administered dose that was excreted in the urine, about 72% was excreted within 6 h after dosing. The results confirmed that ractopamine was extensively and rapidly absorbed, with an oral bioavailability of a minimum of 45.7% of the administered dose. Owing to rapid metabolism, the orally administered dose of 40mg produced low systemic concentrations of parent ractopamine, suggesting significant first-pass metabolism of the drug. The available data strongly suggest that disposition, metabolism, and excretion of ractopamine in humans are consistent with the pharmacokinetics and biotransformation observed in animals and for other phenolic, catecholic, and resorcinolic phenethanolamine beta-adrenergic agents (Hunt, 1994; Smith & Rodewald, 1994; Smith, 1998).
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發表於 2012-3-4 22:01:53
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