Quantitative determination of the macrolide antibiotic tulathromycin in plasma and broncho-alveolar cells of foals using tandem mass spectrometry.

This research developed a high-throughput method using tandem mass spectrometry to measure how the long-acting antibiotic tulathromycin is absorbed, distributed, and eliminated in foals. The study found that after intramuscular administration, tulathromycin was quickly absorbed, widely distributed, and slowly eliminated, accumulating at significant levels in broncho-alveolar cells.

Research Methodology

• The research involved developing a method to measure the disposition and distribution of the antibiotic tulathromycin in foals – specifically, in horse plasma and broncho-alveolar cells.
• ‘Tandem mass spectrometry’ was employed, which is a technique used to analyse the properties of molecules, including drugs, by breaking them down into various fragments.
• The researchers used specific calibration ranges for horse plasma (0.006-0.8 microg/mL) and broncho-alveolar cells (0.1-4.0 microg/10(9) cells).

Testing of Tulathromycin

• Tulathromycin was extracted from both plasma and broncho-alveolar fluid for testing. The extraction process involved using cation exchange cartridges with a solution of acetonitrile and ammonia (95:5, v/v).
• Chromatography, a process used to separate mixtures, was performed isocratically with a mobile phase consisting of ammonium formiate buffer and acetonitrile (30:70, v/v). The isocratic method means using a single, consistent solvent mix throughout the process.

Mass Spectrometry Analysis

• The mass spectrometer, which is used to measure the masses of different molecules within a sample, was operated in selected ion mode with atmospheric pressure chemical ionization. This made it possible to monitor the respective MH+ ions m/z 577.3 for tulathromycin and m/z 679.3 for the internal standard roxithromycin.
• The issue of quality was addressed by ensuring all parameters fulfilled international criteria for bioanalytical method validation.

Results and Conclusion

• The method was applied successfully in determining the distribution of tulathromycin in the plasma of foals and in broncho-alveolar cells.
• The study found that tulathromycin was rapidly absorbed, widely distributed, and slowly eliminated after intramuscular administration.
• Notably, tulathromycin accumulated at significant levels in the broncho-alveolar cells of the foals, providing insights into how the drug behaves in these areas.