Disposition of oral telithromycin in foals and in vitro activity of the drug against macrolide-susceptible and macrolide-resistant Rhodococcus equi isolates.

The research study focuses on understanding the effectiveness of the drug telithromycin in foals against different strains of bacteria Rhodococcus equi, which are either sensitive or resistant to macrolide-category of antibiotics. The experiment tracks how the drug behaves in the body of the foals and compares it against other antibiotics in terms of minimal inhibitory concentration required.

Study Design

• The research was conducted on six healthy foals aged between 6 to 10 weeks. Each subject was administered with an oral dose of 15 mg/kg of body weight of telithromycin. This study was intended to map the activity of the drug in serum, pulmonary epithelial lining fluid (PELF), and bronchoalveolar lavage (BAL) cells over time.
• A laboratory technique called the broth macrodilution method was used to find the minimum concentration (MIC) of various antibiotics – telithromycin, azithromycin, clarithromycin, and erythromycin – that can inhibit the growth of the bacteria Rhodococcus equi.

Results

• Around 1.75 hours post drug administration, the peak serum activity was detected. The average maximum activity was found to be 1.43 microg/mL, with a half-life of about 3.81 hours.
• The concentration of telithromycin in BAL cells compared to PELF or plasma was distinctly higher at the 4-hour mark.
• The inhibitory concentration required of telithromycin for macrolide-resistant strains of R. equi was high at 8 microg/mL, whereas for macrolide-susceptible strains it was lower at 0.25 microg/mL. Despite this, the study noticed that telithromycin showed increased effectiveness compared to other tested antibiotics against macrolide-resistant strains.

Conclusion

• The research revealed that telithromycin concentration in the body peaked in less than 2 hours and reduced by half in about 4 hours. Also, the antibiotic accumulated in a significant manner in certain areas like BAL cells.
• While the macrolide-resistant strains of R. equi needed a higher concentration of telithromycin for inhibition, the antibiotic outperformed others like azithromycin, clarithromycin, and erythromycin, suggesting that this drug might be more effective against such resistant types of the bacteria.