Pharmacokinetics of tramadol and metabolites O-desmethyltramadol and N-desmethyltramadol in adult horses.

The research seeks to establish how a drug called Tramadol and its by-products, O-desmethyltramadol and N-desmethyltramadol, are metabolized in adult horses.

Study Design and Methodology

• The experiment involved 12 mixed-breed adult horses. This sample size and diversity cater to variability across breeds, strengthening the conclusiveness of the results.
• The horses were administered two forms of Tramadol; Intravenous (IV) and oral, separated by a 6-day washout period to eliminate any residual traces of the drug in the horses’ systems. The IV dosage was 5mg/kg over 3 minutes, while the oral dosage was 10mg/kg.
• Serum samples were collected for a period of 48 hours post-administration to study the concentration and metabolic breakdown of Tramadol and its metabolites.
• The concentration of Tramadol, ODT, and NDT in the serum was assessed using high-performance liquid chromatography.
• The data collected was evaluated using non-compartmental analysis to infer pharmacokinetics.

Results

• Following IV administration, the peak mean serum concentrations for Tramadol, ODT, and NDT were reported to be 5,027 ± 638 ng/mL, 0 ng/mL, and 73.7 ± 12.9 ng/mL, respectively. For Tramadol, half-life, volume of distribution, area under the curve, and total body clearance after IV administration were also calculated to provide a comprehensive understanding of the drug’s kinetics.
• After oral administration, the peak serum concentrations for Tramadol, ODT, and NDT were 238 ± 41.3 ng/mL, 86.8 ± 17.8 ng/mL, and 159 ± 20.4 ng/mL, respectively.
• The half-life (time taken for the concentration to reduce to half) for Tramadol, ODT, and NDT after oral administration were quite similar, thus indicating a comparable rate of metabolism for these substances in horses.
• The oral bioavailability of Tramadol (percentage of the administrated drug that reaches systemic circulation) was found to be 9.50 ± 1.28%, indicating that a small fraction of the orally administered drug is available for physiological action.
• The therapeutic concentration range for Tramadol and ODT were maintained for around 2 hours after oral administration, suggesting that the drug’s analgesic effects may last less than 3 hours in horses.

Conclusion

• The study concludes that the oral administration of Tramadol might result in an analgesic duration of less than 3 hours in horses. Interestingly, even the metabolite ODT appears to contribute equally along with the parent drug to this effect.
• This comprehensive pharmacokinetic study can potentially guide the appropriate use and dosage of Tramadol for pain relief in horses and paves the way for further research in this field.