Detection of enrofloxacin and its metabolite ciprofloxacin in equine hair.

The research article presents a developed method for detecting drugs, specifically enrofloxacin and its metabolite ciprofloxacin, in horse hair and investigates their long-term detectability post-administration. It also explores the correlation of drug concentration with variables such as dose, route of administration, and hair color.

Method Development and Recovery

• The research began with the development of a method to analyze enrofloxacin and ciprofloxacin in mane and tail hair of horses. The process involved extracting samples in trifluoroacetic acid at a temperature of 70 degrees Celsius.
• The extracts were then cleaned using solid-phase extraction and analyzed through high-performance liquid chromatography with UV-diode array detection. The recovery rate for the analytes, referring to the percentage of the substance extracted and detected, was found to be over 87%.

Administration and Sampling

• The study involved horses that had been given therapeutic doses of enrofloxacin either orally (7.5mg/kg daily for 3-13 days or twice daily for 10-14 days) in Group 1 (n=7), or intravenously (5.0mg/kg daily for 12 and 15 days) in Group 2 (n=2).
• Samples of enrofloxacin and ciprofloxacin were detected in the hair for up to 10 months after the treatment. The highest concentrations of these drugs were measured at 452 and 19 ng/mg, respectively.

Correlation to Variables and Long-Term Detectability

• The study also examined whether the concentration of the drugs in the horse hair was linked to the dose administered, the route of administration, and the color of the hair. The drug concentration related to the dose of enrofloxacin, with correlations of r2=0.777 for enrofloxacin and r2=0.769 for ciprofloxacin.
• Interestingly, the study found that the absorption of these drugs was much higher in black horse hair compared to white hair. The uptake in black hair was reported to be 40 times more than in white horse’s hair. In vitro, both enrofloxacin and ciprofloxacin were extensively bound to melanin, a pigment that determines hair color, at over 96%.
• The study also discovered that the ratio of enrofloxacin to ciprofloxacin differed after oral and intravenous administration, indicating that the route of administration impacts the concentration of these substances. Furthermore, the longitudinal distributions of these drugs within the hair shafts were found to correlate with the time elapsed since the treatment.