The clinical and histopathologic effects of potentiated chlorhexidine in the upper respiratory tract of horses.
Authors: Stewart Holly L, Engiles Julie B, Richardson Dean W, Levine David G
Journal: Veterinary surgery : VS
Summary
# Editorial Summary: Potentiated Chlorhexidine for Equine Upper Respiratory Tract Treatment Chlorhexidine (CHD) has long been used in equine medicine, but this 2021 investigation examined whether formulating it with EDTA-Tris buffers could enhance its antimicrobial properties whilst remaining safe for direct application to delicate respiratory mucosa. The researchers conducted both in vitro testing against six clinically relevant pathogens (including *Aspergillus fumigatus*, *Streptococcus equi* subspecies, and *Pseudomonas aeruginosa*) and an in vivo safety trial in which eight healthy horses received two topical applications of 0.0005% CHD-EDTA-Tris solution to the upper respiratory tract, with mucosal biopsies subsequently analysed for inflammation or tissue damage. Whilst the 0.005% concentration proved 100% effective against all organisms tested, the clinically practical 0.0005% formulation demonstrated strong bactericidal activity against most species, though slightly reduced efficacy against *A. fumigatus* and *S. equi* ssp. *equi*; critically, no clinical, gross, or histopathologic abnormalities were detected following treatment. For equine practitioners managing upper respiratory infections or inflammatory conditions—particularly those resistant to systemic therapy or where topical access is feasible—this formulation offers a well-tolerated alternative with documented antimicrobial efficacy and safety profile, though practitioners should be mindful that certain organisms may require higher concentrations for reliable kill rates.
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Practical Takeaways
- •0.0005% CHD-EDTA-Tris solution is safe for topical use in the equine upper respiratory tract and can be considered for treating bacterial or fungal respiratory infections without risk of tissue damage
- •Higher concentrations (0.005%) may be needed in vitro for complete efficacy against certain pathogens, but clinical dosing protocols should follow safety data from the lower concentration used in vivo
- •This potentiated chlorhexidine formulation offers a non-damaging antimicrobial option for practitioners treating upper airway infections where conventional treatments may be limited
Key Findings
- •0.005% CHD-EDTA-Tris solution was 100% effective against all bacterial and fungal species tested in vitro, while 0.0005% was less effective against A. fumigatus and S. equi ssp. equi
- •0.0005% CHD-EDTA-Tris caused no clinical, gross, or histologic abnormalities when topically applied twice to the equine upper respiratory tract
- •CHD-containing solutions demonstrated superior fungal and bacterial killing compared to EDTA-Tris alone
- •Short-term topical treatment with dilute CHD was well-tolerated with no inflammatory response observed in equine upper respiratory tissue