Plasma concentrations and pharmacokinetics of erythromycin and related compounds were determined after administration of erythromycin ethylsuccinate to six healthy male foals 3 to 5 months of age. Hay was withheld from the foals overnight and erythromycin ethylsuccinate (25 mg/kg of body weight) was administered intragastrically. Plasma erythromycin concentrations were determined at specific times after drug administration by high-performance liquid chromatography assay. Maximum peak plasma concentrations, time to maximum concentrations, area under plasma concentration versus time curves, elimination half-life, and mean residence time were determined from concentration versus time curves. Maximum peak concentration of erythromycin A (0.45 ± 0.27 μg/ml) after administration of erythromycin ethylsuccinate was observed at 2.38 ± 1.54 hours after treatment. Concentrations of anhydroerythromycin A were maximal at 2.2 ± 2.0 hours and reached a maximum of 2.6 ± 1.9 μg/ml. Plasma concentrations of the ester parent drug (erythromycin ethylsuccinate) were below the limit of quantitation (0.1 μg/ml) at all times except 2.5, 2.75, and 5.5 hours. Levels at those times ranged from 0.1 to 0.144 μg/ml. Erythromycin ethylsuccinate appears to be poorly absorbed after oral administration to fasted foals. Plasma concentrations of erythromycin A remained below 0.25 μg/ml (reported minimum inhibitory concentration for Rhodococcus equi) for less than 4 hours after intragastric administration of erythromycin ethylsuccinate, suggesting that the recommended dosage (25 mg/kg every 6 hours) would be suboptimal for treatment of R. equi infections.
|Original language||English (US)|
|State||Published - 2002|
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