The clinical and histopathologic effects of potentiated chlorhexidine in the upper respiratory tract of horses

Objective To describe the bactericidal and fungicidal properties of a 0.0005% chlorhexidine (CHD) solution potentiated with EDTA‐Tris buffers (CHD‐EDTA‐Tris) and evaluate the safety of 0.0005% CHD‐EDTA‐Tris in the upper respiratory tract (URT) of normal horses. Study Design Clinical, prospective study. Animals Eight healthy, skeletally mature horses. Methods In vitro—serial dilutions of CHD‐EDTA‐Tris and EDTA‐Tris alone were evaluated for bactericidal and fungicidal activity against Aspergillus fumigatus, Escherichia coli, Staphylococcus aureus, Streptococcus equi subspecies ssp. equi, Streptococcus equi ssp. zooepidemicus, and Pseudomonas aeruginosa. In vivo—eight healthy horses were topically treated twice with 30 ml of 0.0005% CHD‐EDTA‐Tris. Mucosal samples from each location were evaluated for the presence of inflammation or pathologic lesions. Results Solutions containing CHD were superior in fungal and bacterial killing to those without. In vitro—a 0.005% CHD‐EDTA‐Tris was 100% effective against all bacterial and fungal species evaluated, while a 0.0005% CHD‐EDTA‐Tris was less efficacious against A. fumigatus and S. equi ssp. equi. In vivo—a 0.0005% CHD‐EDTA‐Tris did not cause any clinical, gross, or histologic abnormalities when topically applied to the equine URT. Conclusions A 0.0005% CHD‐EDTA‐Tris was highly effective for killing of common bacterial and fungal isolates in the equine upper respiratory tract. Short‐term topical treatment of the equine URT with dilute CHD did not cause gross or histological inflammation in the tissue. Clinical Significance A 0.0005% CHD solution with EDTA‐Tris should be considered for treatment of clinically relevant inflammatory or infectious conditions or in the URT of the horse.