Luprostiol is a prostaglandin derivative of the type PGF2a which was developed as a potential agent for estrus synchronization in dairy cows. The depletion of S-35-Luprostiol residues in milk, liver, kidney, fat and muscle was investigated 12 hour, 1 day and 3 days after intramuscular administration of the drug. At a dosage of 15 mg/head, injection site had a residue level of 250 ppb which was the highest tissue residue level detected at 1-day withdrawal. However, the residues were quickly depleted to 11 ppb within 3 days. The residue levels in milk were less than 2 ppb in the first 12 hour sampling period. The metabolic profile in urine was studied by HPLC/MS after a 30 mg/head dose. Several metabolites were detected. The major pathway of degradation was found to be the beta-oxidation of the carboxylic acid side chain. The tissue residue levels at different withdrawal periods, and the metabolic profiles in urine, liver and kidney are presented.
