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Home / Equine Research Bank / Drug Test Anal / Detection of Transdermal Application of Testosterone to Race...
Drug testing and analysis2025; doi: 10.1002/dta.3905

Detection of Transdermal Application of Testosterone to Racehorses by Analysis of Urine and Plasma.

Abstract: The use of testosterone in racehorses is predominantly monitored using international urine and plasma concentration-based thresholds and complementary steroid ratios. To date, there has been no published pharmacokinetic study on transdermally applied testosterone products in horses and whether their use could result in adverse analytical findings. Therefore, quantitative analysis of testosterone and epitestosterone in urine and testosterone in plasma samples was performed following a pilot multi-dose transdermal Testogel administration (1 mg/kg once a day for 7 days on clipped skin) to one gelding and one mare. The peak concentrations (C) of free testosterone were 1060 and 1800 pg/mL in gelding and mare plasma, respectively. Testosterone concentrations exceeded the international plasma threshold of 100 pg/mL consistently for up to 4 h post-administration, after which detection above the threshold was sporadic up to 127 h. In urine, C of free and conjugated (sulfate and glucuronide) testosterone were 700 and 323 ng/mL in gelding and mare urine, respectively. In the gelding, testosterone concentrations exceeded the international urine threshold of 20 ng/mL consistently for up to 47 h post-administration, but sporadically up to 143 h. In all samples, testosterone: epitestosterone ratios were greater than 5, another requirement for adverse analytical findings in geldings. In the mare, testosterone concentrations exceeded the urine threshold of 55 ng/mL consistently for up to 71 h post-administration, but sporadically up to 167 h. Therefore, these limited results for one gelding and one mare demonstrate that doping control following transdermal applications of testosterone to racehorses is possible using existing approaches.
© 2025 John Wiley & Sons Ltd.
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Publication Date: 2025-06-03 PubMed ID: 40461131DOI: 10.1002/dta.3905Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article focuses on the detection of transdermally applied testosterone in racehorses through quantitative analysis carried out on their urine and plasma samples.

Research Background

  • The study was necessitated by the realization that there are no existing pharmacokinetic studies exploring the impact of transdermally applied testosterone in horses or the possible negative findings that could result from their use.
  • The commonly used approaches to monitor the use of testosterone in racehorses currently involve international concentration-based thresholds and complementary steroid ratios measured in urine and plasma.

Methodology

  • In the testing protocol, a pilot multi-dose of Testogel, a transdermal testosterone product, was administered at 1mg/kg daily for seven days to clipped skin on a gelding (a castrated male horse) and a mare (a female horse).
  • Subsequently, the concentrations of testosterone and epitestosterone were quantified in urine and testosterone in plasma samples from both horses.

Results

  • The peak concentrations of free testosterone post-administration reached 1060 and 1800 pg/mL for the gelding and mare plasma respectively.
  • Testosterone concentrations in plasma exceeded the international threshold of 100 pg/mL for up to 4 hours post administration, with sporadic detection above this threshold up to 127 hours later.
  • In urine samples, the peak concentrations of free and conjugated testosterone (in sulfate and glucuronide form) were identified as 700 and 323 ng/mL in gelding and mare urine respectively.
  • In the gelding’s samples, testosterone concentrations remained above the international urine threshold of 20 ng/mL for up to 47 hours post administration, with random detection above this value lasting up to 143 hours.
  • Importantly, the testosterone:epitestosterone ratios in all samples were greater than 5, which is a requirement for an adverse analytical finding in geldings.
  • In the mare’s samples, testosterone concentrations were consistently above the urine threshold of 55 ng/mL for up to 71 hours post administration, and sporadically above that threshold for up to 167 hours.

Conclusion

  • The study offers preliminary evidence that using existing methods to control doping is possible following transdermal applications of testosterone to racehorses. More specifically, it can be detected in urine and plasma samples taken from those horses.
  • However, it’s worth noting that the research was limited to one gelding and one mare, thereby pointing to the need for further and more extensive studies on this subject.

Cite This Article

APA
Viljanto M, Cutler C, Habershon-Butcher J, Hincks P, Scarth J. (2025). Detection of Transdermal Application of Testosterone to Racehorses by Analysis of Urine and Plasma. Drug Test Anal. https://doi.org/10.1002/dta.3905

Publication

Drug testing and analysis
ISSN: 1942-7611
NlmUniqueID: 101483449
Country: England
Language: English

Researcher Affiliations

Viljanto, Marjaana
  • LGC, Fordham, Cambridgeshire, UK.
Cutler, Charlotte
  • LGC, Fordham, Cambridgeshire, UK.
Habershon-Butcher, Jocelyn
  • British Horseracing Authority, London, UK.
Hincks, Pamela
  • LGC, Fordham, Cambridgeshire, UK.
Scarth, James
  • LGC, Fordham, Cambridgeshire, UK.

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