Tissue distribution of clenbuterol in the horse.

The research investigates the distribution and retention period of the drug clenbuterol (CLB) in different body tissues of a horse after oral administration. This study uncovered that the highest concentrations of CLB were found in certain tissues, contributing to the drug’s prolonged elimination and detectability.

Methodology

• The study was carried out on horses given an oral dose of clenbuterol (1.6 microg/kg) twice daily for two weeks.
• The horses were terminated at different time intervals (0.25, 24, 48, and 72 hours) after the last administered dose. This allowed the researchers to observe the concentration of the drug at different points in time.

Results

• The maximum clenbuterol concentration, within a quarter of an hour of the last dosage, was found in the liver (16.21 ng/g), followed by the lung, left ventricle, kidney, bronchi, right ventricle, and eye fluids. This concentration was notably higher than what was found in the plasma (1.10 ng/mL).
• The half-lives—that is, the time taken for the clenbuterol concentration to reduce by half—ranged from 21.2 to 56.3 hours in various tissues. The longest half-lives were observed in the eye fluids (56.9 hours), spleen, cerebrum, cerebellum, and cecum.
• The half-life for plasma, in contrast, was 10.9 hours.

Conclusion

• The research found that the tissue/plasma ratios of liver, lung, left ventricle, kidney, bronchi, and right ventricle remained high up to 72 hours post-administration.
• The elevated concentration of clenbuterol in these tissues, compared to plasma, contributed to the drug’s ability to remain in the system for a protracted period. Such a sustained level of concentration further allowed for the quantification of clenbuterol in plasma and urine over an extended duration.