Plasma profiles of ivermectin in horses following oral or intramuscular administration.

The study compares plasma dispositions of ivermectin in horses given either orally or via intramuscular injection. The results indicate that different administration methods have significant impacts on the absorption, bioavailability and elimination half-life of this drug.

Objective and Methodology

• The main objective was to evaluate and compare ivermectin’s plasma kinetic parameters after oral or intramuscular administration in horses.
• Two experimental groups of horses were used, each comprising five clinically healthy adult horses, weighing between 380-496 kg body weight (BW).
• Group I were treated orally with ivermectin paste at a dose of 0.2 mg/kg BW, whereas Group II were treated with an intramuscular injectable formulation of ivermectin at the same dose.
• Blood samples were taken from the subjects at different times, ranging from 0.5 hour to 75 days post-treatment, and analysed by high-performance liquid chromatography with fluorescence detection.
• A computerized kinetic analysis was performed and data was compared to identify significant differences.

Results

• Ivermectin was detected in plasma between 30 minutes and either 20 days (for oral) or 40 days (for IM) post-treatment.
• Significant differences were found between the two groups in regards to the time taken to reach peak plasma concentrations, and for absorption half-life.
• Peak plasma concentrations were 51.3 +/- 16.1 ng/ml after oral administration and 31.4 +/- 6.0 ng/ml for the IM route.
• The values for the area under the concentration-time curve were markedly higher for the horses given IM treatment (303.2 +/- 4.3 ng day/ml), compared to those who received the drug orally (137.1 +/- 35.9 ng day/ml).
• The mean plasma residence times were 4.2 +/- 0.4 days for orally treated horses and 8.9 +/- 0.7 days for IM-treated groups.

Conclusion

• The study found that the route of administration dramatically affects the disposition of ivermectin in horses. The intramuscular route showed a much higher bioavailability and elimination half-life than oral administration.
• The study also established a correlation between the pharmacokinetic profiles and the clinical efficacy of ivermectin, suggesting that the method of administration might impact the drug’s effectiveness.