Azithromycin in the treatment of pneumonic foals
Bethany L Bramwell1, Lavonn A Williams
1Walgreen Drug Stores, West Plains, Missouri.
Abstract:
Rhodococcus equi, one of the most common causes of pneumonia in foals between 3 weeks and 5 months of age, is a troublesome disease. For many years, Rhodococcus equi pneumonia carried a very poor to grave prognosis due to the lack of a good treatment protocol. However, antibiotics that are very good at treating the infection have been identified. Through research we have begun to further understand the epidemiology of the disease, acquired an arsenal of suitabe treatment options, and identified prevention strategies that are actively being studied. Oral erythromycin requires multiple daily dosing, has inconsistent absorption rates in foals, and a growing number of resistant Rhodococcus equi isolates have been identified. Azithromycin and clarithromycin have been proposed as alternatives to erythromycin for the treatment of Rhodococcus equi. Studies in other species have demonstated that azithromycin has better pharmacokinetics and is safer than erythromycin. Azithromycin has shown high and sustained intracellular and tissue concentrations with levels still high 48 hours after administation of the last oral dose. Azithromycin is commercially available in 250-mg and 500-mg tablets, and 100-mg/5 mL and 200-mg/5-mL oral suspensions. Oral pastes and powder feed additives in various concentrations and flavors can be formulated by compounding pharmacists.
Insights
Rhodococcus equi pneumonia in foals is a significant concern. Azithromycin offers a promising alternative to erythromycin, showing better pharmacokinetic properties and sustained efficacy for treating this challenging equine respiratory disease.
Area of Science:
- Veterinary Medicine
- Equine Health
- Infectious Diseases
Background:
- Rhodococcus equi causes significant pneumonia in foals (3 weeks to 5 months).
- Historically, Rhodococcus equi pneumonia had a poor prognosis due to limited treatment options.
- Emerging antibiotic resistance to erythromycin necessitates alternative treatments.
Purpose of the Study:
- To evaluate azithromycin as an alternative to erythromycin for Rhodococcus equi treatment in foals.
- To investigate the pharmacokinetic and safety profile of azithromycin compared to erythromycin.
- To explore novel treatment and prevention strategies for Rhodococcus equi infections.
Main Methods:
- Literature review of Rhodococcus equi epidemiology and treatment options.
- Comparative analysis of antibiotic pharmacokinetics and efficacy in equine models (implied).
- Assessment of azithromycin's tissue and intracellular concentrations post-administration.
Main Results:
- Azithromycin demonstrates superior pharmacokinetic properties and safety compared to erythromycin in other species.
- Azithromycin achieves high and sustained intracellular and tissue concentrations, remaining elevated 48 hours post-treatment.
- Multiple formulations of azithromycin are commercially available and can be compounded.
Conclusions:
- Azithromycin represents a viable and potentially more effective alternative for treating Rhodococcus equi pneumonia in foals.
- Further research into azithromycin's efficacy and optimal dosing in foals is warranted.
- Improved treatment protocols are crucial for managing this common equine foal disease.
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