Pharmacokinetics of metronidazole given to horses by intravenous and oral routes.

This research explores how the drug metronidazole is processed in the bodies of healthy horses. The study found that absorption and elimination of the drug vary depending on whether it is given intravenously or orally, but in both instances, its concentration in peritoneal fluid mirrored that in serum. The researchers suggest a daily dosage of 15 to 25 mg/kg for maximal effectiveness against anaerobic bacteria.

Methods and Subjects

• The researchers conducted their study on 6 healthy adult horses. These horses were given Metronidazole, a common antibacterial and antiprotozoal drug, in a controlled setting to study its pharmacokinetics.

Research Findings

• Following the intravenous (IV) administration of the drug, it followed a two-compartment model for disposition in the body. This is a commonly used pharmacokinetic model which assumes the body has two compartments – one that rapidly distributes the drug and another that eliminates it more slowly.
• The distribution half-life of the drug, or the time taken for the drug’s concentration to decrease by half in the distribution phase, was 0.16 hours.
• The elimination half-life, the time taken for the drug’s concentration to decrease by half during the elimination phase, was 2.9 hours.
• Body clearance, the volume of plasma from which the drug is completely removed per unit time, was calculated to be 0.40 +/- 0.05 L/kg/hr. This indicates a higher clearance rate, meaning the drug is eliminated from the body relatively quickly.
• For oral administration of the drug, the absorption half-life was noted to be 0.40 hours, indicating it’s absorbed at a slower rate as compared to IV administration.
• The bioavailability, or the proportion of the drug that enters circulation and able to have an active effect, was found to be 85.0 +/- 18.6%, confirming that a significant portion of the orally-administered drug was successfully absorbed by the horse’s body.
• Metronidazole concentration in the peritoneal fluid was about equal to its concentration in the serum. This was consistent across both routes of administration, indicating that the drug equally distributes between these two body compartments.

Recommendations

• Based on minimum inhibitory concentrations reported for anaerobic bacteria – bacteria that can grow without oxygen – the researchers recommend a dosage of 15 to 25 mg/kg of Metronidazole to be given orally 4 times daily for effective treatment. This dosage is suggested based on how well the horses absorbed and metabolized the drug.