Rectal administration of metronidazole with and without rectal evacuation prior to use in horses.

This study examined the effects of rectal evacuation on the absorption of the drug metronidazole in horses, with findings suggesting there is no benefit to manually evacuating a horse’s rectum before drug administration.

Research Methodology

• The study utilized a randomized crossover design including 10 adult horses. In this method, each horse acts as its own control, thereby reducing potential error caused by individual differences among the horses.
• The researchers administered crushed metronidazole tablets rectally at a dosage of 20 mg/kg to each horse.
• This was done with two different interventions. In some cases, the horses’ rectums were evacuated (referred to as group E) before the drug administration. In other cases, no evacuation was carried out (referred to as group NE).
• Serum samples from the horses were collected over a 24-hour period following administration. The purpose was to determine plasma concentrations of the drug over time.

Findings

• Using high-pressure liquid chromatography, the investigators were able to determine the plasma concentrations of the drug in the samples.
• At 15 minutes post-administration, the group E horses that had prior rectal evacuation had significantly higher plasma concentrations of the drug (p = 0.027). However, there were no concentration differences at any other time points.
• Large variability was observed in the relative bioavailability (the extent and rate at which the active moiety is absorbed from a drug product and becomes available at the site of drug action) in the NE group, with a median value of 86.7%.

Conclusion and Recommendations

• The study concludes that based on the results, there is no advantage to manually evacuating a horse’s rectum prior to rectal administration of metronidazole.
• The investigators suggest further studies at higher dosages, as well as examination of clinical efficacy, based on these findings. Clinical efficacy refers to how effective the drug is in actual real-world conditions, so future studies should examine whether the drug is truly effective in treating the conditions it targets when administered in the manner tested.