Pharmacokinetics of metronidazole in horses after intravenous, rectal and oral administration.

This research investigates the pharmacokinetics—how drugs move within the body—of the antibiotic metronidazole in horses, comparing how it is absorbed and processed when administered orally, rectally, and intravenously.

Study Design and Measurement

• The research was based on a triple crossover study design; a type of experiment where the same subjects—here, horses—are split into different groups to receive different treatments—in this case, the route of drug administration—at different times.
• The drug was administered at a dosage of 20mg/kg using three different routes: intravenous (IV), rectal (PR), and oral (PO).
• Parameters like the drug’s half-life after administration, its clearance rate, the volume of distribution at a steady state, and time taken to reach maximum serum concentration were measured and compared. The bioavailability—meaning the degree and rate at which the drug is absorbed into a living system and becomes available—after each type of administration was also evaluated.

Key Results

• The half-life of metronidazole was found to be the longest after oral administration (240+/-65 min), followed by rectal (212+/-30 min), and then intravenous administration (196+/-39 min). The half-life implies the time taken for the concentration of the drug in the body to reduce by half.
• The volume of distribution at a steady state was 0.68 L/kg. The volume of distribution is a theoretical volume that a drug would have to occupy to provide the same concentration as it does in blood serum if it was uniformly distributed throughout the body.
• The clearance rate of the drug was measured to be 2.8 mL/min/kg, indicating the volume of blood from which the drug is removed per unit of time.
• The bioavailability and maximum serum concentration were significantly higher after oral administration as compared to rectal administration. However, there were no significant differences in mean absorption time and time to reach maximum serum concentration between the two.

Conclusions

• The study concludes that while the oral administration of metronidazole in horses provides better bioavailability, rectal administration offers a usable alternative when oral administration is not possible.
• These findings provide relevant guidelines on choosing the administration route of metronidazole in equine patients, considering both drug effectiveness and practical conditions.