Simultaneous determination of erythromycin ethylsuccinate and its metabolite erythromycin in human plasma using liquid chromatography–electrospray ionization mass spectrometry for clinical study

A sensitive and selective liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method was developed for simultaneous identification and quantification of erythromycin ethylsuccinate and erythromycin in human plasma, which can be well applied to clinical study. The method was based on liquid-liquid extraction, followed by a LC procedure with an ODS C18 column, and mixture of acetonitrile and 1.67 mmol/l acetic acid as mobile phase. MS detection was performed using a single quadrupole mass spectrometer in positive selected ion monitoring (SIM) mode. The method was validated to be linear, precise and accurate. The lower limit of quantification of erythromycin ethylsuccinate and erythromycin were both 0.5 ng/ml. The proposed method enables the unambiguous identification and quantification of erythromycin ethylsuccinate and erythromycin for clinical drug monitoring.

Pharmacokinetics of erythromycin ethylsuccinate after intragastric administration to healthy foals

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 microg/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 microg/ml. Plasma concentrations of the ester parent drug (erythromycin ethylsuccinate) were below the limit of quantitation (0.1 microg/ml) at all times except 2.5, 2.75, and 5.5 hours. Levels at those times ranged from 0.1 to 0.144 microg/ml. Erythromycin ethylsuccinate appears to be poorly absorbed after oral administration to fasted foals. Plasma concentrations of erythromycin A remained below 0.25 microg/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.

[Comparison of the bioavailabilities of erythromycin estolate and erythromycin ethylsuccinate dry suspension preparations in steady state]

Relative bioavailability of erythromycin was determined after multiple-dose administration of erythromycin estolate in comparison to erythromycin ethylsuccinate both given as oral suspensions to twelve healthy volunteers. The daily erythromycin dose of erythromycin ethylsuccinate was 50% higher than the respective dose of erythromycin estolate; the dosage interval tau was 12 h for erythromycin estolate and 8 h for erythromycin ethylsuccinate. This scheme was planned in accordance to advices of the respective manufactures. Results of the study confirm the differences in extent of bioavailability of both erythromycin derivatives known from single-dose investigations. Furthermore, the experimental data show that a twice daily administration of 1000 mg erythromycin as erythromycin estolat resulted in sufficiently high plasma concentration of the active compound.

Bioanalysis of erythromycin 2'-ethylsuccinate in plasma using phase-system switching continuous-flow fast atom bombardment liquid chromatography-mass spectrometry

A specific method for the determination of erythromycin 2'-ethylsuccinate (EM-ES) in plasma is described. The method involves a liquid-liquid extraction procedure followed by the analysis of extracts using phase-system switching (PSS) continuous-flow fast atom bombardment (CF-FAB) liquid chromatography-mass spectrometry (LC-MS). In PSS EM-ES is enriched after analytical separation on a short trapping column, from which it is desorbed to the LC-MS interface. In this way, favourable mobile phases can be used for the LC separation and for the MS detection. Using the PSS approach a flow-rate reduction from 1.0 ml/min in the LC system to 15 microliters/min going into the mass spectrometer was achieved without splitting. The determination limit for EM-ES was 0.1 microgram/ml.

[Study on serum and urine concentrations of erythromycin succinate of pyrrolidine-methyl-tetracycline]

The serum and urine antibiotic levels in a group of 25 patients were determined after a single administration of a new antibiotic salt: erythromycin succinate of pyrrolidine-methyl-tetracycline. Some subjects were treated orally and other intramuscularly. The results obtained showed that this drug gives, both orally and intramuscularly, efficient serum and urine concentrations of tetracycline and erythromycin.