Pharmacokinetics and pulmonary distribution of gamithromycin after intravenous administration in foals

The long-acting azalide antibiotic gamithromycin is marketed for intramuscular treatment of bovine and swine infections. Off-label use in foals leads to severe local lesions likely caused by hyperosmolality of the injected solution. We provide evidence from a pharmacokinetic study in 10 warm-blooded healthy foals for intravenous bolus injection of gamithromycin diluted in distilled water to be a safe and well tolerated alternative. By intravenous dosing, markedly higher plasma exposure and better penetration into bronchoalveolar lavage cells but lower distribution into epithelial lining fluid are achieved as after intramuscular or subcutaneous administration. Intravenously injected gamithromycin was tolerated without any adverse drug reactions. The protocols for treatment of equine pulmonary infections caused by Rhodococcus equi should be revised accordingly.