Trimethoprim-sulfonamide: a valid antimicrobial treatment in foals

Trimethoprim-sulfonamide: a valid antimicrobial treatment in foals?
J Am Vet Med Assoc. 2024 Mar 13:1-9. doi: 10.2460/javma.23.09.0536. Online ahead of print.
Authors
Kajsa Gustafsson 1 , Benjamin W Sykes 2 , Denis Verwilghen 3 4 , Katrien Palmers 5 , Stacey Sullivan 4 , Gaby van Galen 3 4
Affiliations

1 1Department of Veterinary Medicine and Animal Science (DIVAS), University of Milan, Lodi, Italy.
2 2Faculty of Sciences, Southern Cross University, Lismore, NSW, Australia.
3 3Sydney School of Veterinary Sciences, University of Sydney, Camperdown, NSW, Australia.
4 4Goulburn Valley Equine Hospital, Congupna, VIC, Australia.
5 5Equine Clinic De Morette, Asse, Belgium.

PMID: 38479105
DOI: 10.2460/javma.23.09.0536

Abstract

Trimethoprim-sulfonamide (TMPS) combinations are widely used to treat a range of infectious diseases in horses, but some equine practitioners are reluctant to use them for treatment of both neonatal and older foals. Considering the emergence of increased antimicrobial resistance, the use of protected antimicrobials commonly prescribed to foals should be avoided and alternative first-line therapy considered, where appropriate. This review examines the characteristics and pharmacokinetics of TMPS and its suitability for treatment of foals. Data regarding dosage and route of administration are reported on the basis of recent publications in foals. The review intends to share significant information about the common infections that are most likely responsive to TMPS treatment in foals and, as such, where TMPS might be considered a suitable first-line therapeutic option.

Conclusions
Trimethoprim-sulfonamide combinations are safe to administer to foals and without reported side effects when administered at a dosage of 24 mg/kg every 12 hours PO or 15 mg/kg every 12 hours IV. The oral dosage of 24 mg/kg every 12 hours PO reaches serum/plasma concentrations above MIC90 for relevant pathogens. Bacterial susceptibility is variable and varies considerably among geographical areas and laboratory facilities. The use of α-2 agonists with intravenous TMPS should be avoided.

On the basis of the available published evidence, TMPS can be suggested as empirical treatment for the following conditions in foals: perioperative antimicrobial coverage, diarrhea (against translocating bacteria via the affected gut wall and sepsis), most pneumonia causes (except Rhodococcus spp and pulmonary abscesses), wounds, septic arthritis, osteomyelitis, and umbilical infections (without associated abscessation). In the presence of purulent or necrotic tissue, TMPS is not a treatment of choice. However, following surgical debridement and/or lavage, it can be considered a reasonable choice. Foals presented for sepsis should be administered TMPS empirically only if the general TMPS susceptibility in the respective geographic area is known to be good and in cases in which short or no hospitalization periods (ie, lower risk of development of resistant nosocomial infections) are anticipated.