Pharmacokinetics of erythromycin ethylsuccinate after intragastric administration to healthy foals.

The study explores the efficacy of erythromycin ethylsuccinate when orally administered to young, healthy male foals and its effectiveness in battling Rhodococcus equi infections, a common bacterium affecting horses. It concluded that the recommended dosage might not be adequate for treating these infections.

Study Procedure

The research involved six healthy male foals aged between three to five months. The following steps depict the process followed in this research:

• The foals were deprived of hay over the night before the administration of the drug.
• Erythromycin ethylsuccinate, an antibiotic used commonly for bacterial infections, was given to the foals intragastrically at a dosage of 25 mg per kg of body weight.
• Using high-performance liquid chromatography assays, plasma erythromycin concentrations were determined at specified times post drug administration.

Data and Results

The researchers were interested in specifics such as:

• Maximum peak plasma concentrations
• Time to reach these maximum concentrations
• The area under plasma concentration versus time curves
• Elimination half-life
• Mean residence time

The test results indicated that the maximum peak concentration of erythromycin A (0.45 +/- 0.27 microg/ml) was observed approximately 2.38 +/- 1.54 hours post treatment. Concentrations of anhydroerythromycin A, a related compound, peaked around the same time and slightly higher (2.6 +/- 1.9 microg/ml). However, the plasma concentrations of the parent drug, erythromycin ethylsuccinate, were almost negligible and were detectable only at specific hours post-administration.

Conclusion and Implications

The study concluded that erythromycin ethylsuccinate seems to be poorly absorbed when orally administered to fasted foals. The plasma concentrations of erythromycin A, a key ingredient in battling the bacterium Rhodococcus equi, stayed below the minimum inhibitory concentrations for less than 4 hours following the drug’s administration. This data led the researchers to suggest that the standard dosage of 25 mg/kg every 6 hours might be insufficient in effectively treating Rhodococcus equi infections in foals. Further research is needed to determine the optimal dosage for this specific application.