Comparison of oral erythromycin formulations in the horse using pharmacokinetic profiles.

The study investigates the effectiveness of four different formulations of erythromycin, an antibiotic, in horses. The researchers found that two versions of the drug (phosphate and stearate) provided equivalent or potentially better effects compared to the other two versions studied, when used to treat a specific form of pneumonia in horses.

Study Methodology and Key Metrics

• The researchers compared the pharmacokinetic properties (how the body absorbs, distributes, metabolizes, and excretes a drug) of four erythromycin formulations: estolate, phosphate, stearate, and ethylsuccinate.
• These formulations were given to six adult horses in both single and multiple oral doses. The estolate and phosphate were given every 12 hours (at a dosage of 37.5 mg/kg), while the stearate and ethylsuccinate were given every 8 hours (at 25 mg/kg).
• The main performance metrics were the area under the curve (AUC, which signifies drug exposure over time) and the maximum plasma erythromycin concentrations (Cmax).

Study Findings

• The AUC and Cmax values for erythromycin phosphate and stearate were equal or greater compared to those for erythromycin estolate or ethylsuccinate.
• When comparing an 8-hour dosage interval to a 12-hour one for erythromycin phosphate or estolate, no significant differences were found in AUC, peak-trough plasma concentrations, or the duration that plasma concentrations exceeded the minimal inhibitory concentration (MIC) for Rhodococcus equi (a bacterium causing pneumonia in young horses).
• Comparisons were made between single and multiple doses for each formulation, finding differences in Cmax, tmax (time to achieve maximum plasma concentration), and t1/2 beta (elimination half-time) for erythromycin ethylsuccinate and estolate.

Implications and Conclusions

• Based on equivalent plasma antibiotic concentrations, erythromycin phosphate or stearate could be an effective substitute for estolate in the treatment of Rhodococcus equi pneumonia.
• The study found no advantage to administering the drug every 8 hours versus every 12 hours.
• Ultimately, this research could influence treatment protocols for equine pneumonia, potentially leading to improved treatment outcomes with different erythromycin formulations.