Doping Control of Ranitidine in Horses.
Abstract: Ranitidine is a histamine H-receptor antagonist commonly used to treat gastric ulceration in horses. The author's laboratory conducted a study some years ago in the early 2000s on its metabolism as well as its urinary elimination profile in two geldings. With the technology advancement as well as popularity of blood for doping control testing, the laboratory has recently conducted another administration trials of the substance in six horses to study the in vivo metabolism of ranitidine, aiming to identify and reinvestigate the appropriate target(s) for controlling misuse of ranitidine in horses as well as to study its elimination in blood. To study the elimination and biotransformation of ranitidine, administration experiments were performed by giving six castrated horses (geldings) each 25 mL of Ulcerguard oral paste (equivalent to 9.8 g of ranitidine) in the morning and 20 mL of oral paste (equivalent to 7.9 g of ranitidine) in the afternoon daily for eight consecutive days. The postulated in vivo metabolites included ranitidine-S-oxide (M1), ranitidine-N-oxide (M2), desmethylranitidine (M3a/b) and furoic acid analogue of ranitidine (M4), resulting from oxidation, demethylation and oxidative deamination of ranitidine. To control the misuse of ranitidine in horses, elimination profiles of urinary and plasma ranitidine were established. Free ranitidine was detectable for at most 8 days and 72 h in urine and plasma, respectively. Both metabolites ranitidine-S-oxide and ranitidine-N-oxide were detected for 8 days, and therefore, they could be monitored alongside the parent drug as evidence that the substance has gone through the horse's body.
© 2025 John Wiley & Sons Ltd.
Publication Date: 2025-05-20 PubMed ID: 40394757DOI: 10.1002/dta.3909Google Scholar: Lookup
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Summary
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The research investigates the metabolism and elimination profile of ranitidine, a common treatment for gastric ulceration in horses. It also aims to establish methods for controlling the misuse of this drug in the sport of horse racing.
Study Approach
- The research team administered regular doses of ranitidine to six geldings (castrated male horses) over eight consecutive days.
- Ranitidine was delivered via Ulcerguard oral paste, chosen for its efficacy and popularity.
- The amount of ranitidine was measured as 9.8g in the morning dose and 7.9g in the afternoon dose.
Metabolites Investigated
- Ranitidine is metabolized into specific substances in the horse’s body: ranitidine-S-oxide (M1), ranitidine-N-oxide (M2), desmethylranitidine (M3a/b) and furoic acid analogue of ranitidine (M4).
- These metabolites result from the processes of oxidation, demethylation, and oxidative deamination of ranitidine.
Results and Implications
- The researchers established elimination profiles of urinary and plasma ranitidine.
- They found that free ranitidine was detectable for a maximum of 8 days in urine and 72 hours in plasma.
- Two metabolites, ranitidine-S-oxide and ranitidine-N-oxide, were both detectable for 8 days.
- As these metabolites can be detected alongside the parent drug, they can be used as evidence that ranitidine has passed through the horse’s systems, serving as markers to control the misuse of ranitidine in horse racing.
- The research team administered regular doses of ranitidine to six geldings (castrated male horses) over eight consecutive days.
- Ranitidine was delivered via Ulcerguard oral paste, chosen for its efficacy and popularity.
- The amount of ranitidine was measured as 9.8g in the morning dose and 7.9g in the afternoon dose.
Metabolites Investigated
- Ranitidine is metabolized into specific substances in the horse’s body: ranitidine-S-oxide (M1), ranitidine-N-oxide (M2), desmethylranitidine (M3a/b) and furoic acid analogue of ranitidine (M4).
- These metabolites result from the processes of oxidation, demethylation, and oxidative deamination of ranitidine.
Results and Implications
- The researchers established elimination profiles of urinary and plasma ranitidine.
- They found that free ranitidine was detectable for a maximum of 8 days in urine and 72 hours in plasma.
- Two metabolites, ranitidine-S-oxide and ranitidine-N-oxide, were both detectable for 8 days.
- As these metabolites can be detected alongside the parent drug, they can be used as evidence that ranitidine has passed through the horse’s systems, serving as markers to control the misuse of ranitidine in horse racing.
- Ranitidine is metabolized into specific substances in the horse’s body: ranitidine-S-oxide (M1), ranitidine-N-oxide (M2), desmethylranitidine (M3a/b) and furoic acid analogue of ranitidine (M4).
- These metabolites result from the processes of oxidation, demethylation, and oxidative deamination of ranitidine.
Results and Implications
- The researchers established elimination profiles of urinary and plasma ranitidine.
- They found that free ranitidine was detectable for a maximum of 8 days in urine and 72 hours in plasma.
- Two metabolites, ranitidine-S-oxide and ranitidine-N-oxide, were both detectable for 8 days.
- As these metabolites can be detected alongside the parent drug, they can be used as evidence that ranitidine has passed through the horse’s systems, serving as markers to control the misuse of ranitidine in horse racing.
- The researchers established elimination profiles of urinary and plasma ranitidine.
- They found that free ranitidine was detectable for a maximum of 8 days in urine and 72 hours in plasma.
- Two metabolites, ranitidine-S-oxide and ranitidine-N-oxide, were both detectable for 8 days.
- As these metabolites can be detected alongside the parent drug, they can be used as evidence that ranitidine has passed through the horse’s systems, serving as markers to control the misuse of ranitidine in horse racing.
Cite This Article
APA
Ho HSM, Mizzi JX, Ho ENM, Wong WT.
(2025).
Doping Control of Ranitidine in Horses.
Drug Test Anal.
https://doi.org/10.1002/dta.3909 Publication
Researcher Affiliations
- Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, Hong Kong SAR, China.
- Department of Regulation, Welfare and Biosecurity Policy, The Hong Kong Jockey Club, Sha Tin Racecourse, Hong Kong SAR, China.
- Racing Laboratory, The Hong Kong Jockey Club, Sha Tin Racecourse, Hong Kong SAR, China.
- Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, Hong Kong SAR, China.
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