Pharmacokinetics of altrenogest in horses.

The research article focuses on understanding the pharmacokinetics, or how the drug altrenogest moves within the horse’s body. It also discusses its potential misuse in competition horses and reports findings from an elimination study using ten horses.

Study Objective and Background

• The study primarily aimed to investigate the pharmacokinetics of altrenogest in horses. Pharmacokinetics refers to how a drug is absorbed, distributed, metabolized, and excreted in an organism, in this case, horses.
• The background to this study is the use of altrenogest in competition horses. Altrenogest is a drug allowed by the Federation Equestre Internationale for use in mares to control oestrus – the period of sexual receptivity in female mammals.
• However, there is concern that altrenogest can be misused for its potential anabolic effects – enhancing performance by promoting protein synthesis and muscle growth, and suppressing typical male behaviour, making it a controlled substance in competition horses.

Study Design and Methods

• The researchers conducted an elimination study to evaluate the pharmacokinetics of altrenogest. This type of study looks at how a drug is eliminated from an organism – in this case, how horses eliminate altrenogest from their bodies.
• Five oral doses of 44 micrograms per kilogram ((µg/kg)) of altrenogest were administered to ten horses at a dose interval of 24 hours.
• After administration, the researchers collected blood and urine samples from the horses at appropriate intervals to measure the concentrations of altrenogest. The measurements were done using liquid chromatography-tandem mass spectrometry, a technique used to identify and quantify small molecules like altrenogest in biological samples.

Study Findings and Conclusion

• The study found that after administration, the plasma levels of altrenogest reached maximum concentrations ranging from 23 to 75 nanograms per milliliter (ng/mL).
• The baseline values, or typical levels of altrenogest in the blood, were achieved within three days after the final administration.
• The peak concentrations of altrenogest in urine ranged from 823 to 3895 ng/mL. Twelve days after the final administration, concentrations in urine were below the limit of detection, approximately 2 ng/mL.
• These findings provide insight into the pharmacokinetics of altrenogest in horses and may be useful in preventing the misuse of this substance in competition horses.