Presumed Sulfonamide-Associated Uveitis With Stevens-Johnson Syndrome in a Quarter Horse Mare.
Authors: Potocnik Eva, Drozdzewska Karolina, Schwarz Bianca
Journal: Journal of equine veterinary science
Summary
# Editorial Summary This case report documents a rare but severe adverse drug reaction in a four-year-old Quarter Horse mare treated with trimethoprim-sulfadiazine (TMPS) for presumed respiratory infection caused by *Acinetobacter johnsonii*. Within days of TMPS administration, the mare developed bilateral anterior uveitis with ocular discharge alongside systemic signs including fever, productive cough, and disorientation, followed by progressive facial oedema affecting the eyelids, lips, and periorbital region. By day five, whilst the uveitis improved substantially with intensive topical (atropine and corticosteroids) and systemic treatment (cefquinome and flunixin-meglumine), the mare exhibited characteristic mucocutaneous sloughing of the periorbital skin, muzzle, and vulva—clinical signs consistent with Stevens-Johnson syndrome (erythema multiforme major). Although sulfonamide-associated uveitis and SJS are well-documented adverse reactions in humans, this appears to be the first confirmed case in equine medicine, warranting heightened clinician awareness of this potentially life-threatening reaction. Given the widespread use of TMPS in equine practice for respiratory and other infections, practitioners should maintain a high index of suspicion for drug-induced uveitis or mucocutaneous reactions, particularly when these develop concurrent with or shortly after sulfonamide administration, and consider alternative antimicrobials in cases presenting with ocular inflammation or unexplained facial swelling.
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Practical Takeaways
- •Be alert to the rare possibility of Stevens-Johnson syndrome and uveitis when using sulfonamides in horses; discontinue immediately if facial edema, eye discharge, or skin sloughing develops
- •While sulfonamide-associated uveitis is uncommon in horses compared to humans, consider alternative antibiotics (such as cephalosporins) for respiratory infections to avoid this potentially serious adverse reaction
- •Monitor treated horses closely for systemic signs (fever, facial swelling, skin changes) in addition to localized ocular signs when sulfonamides are prescribed
Key Findings
- •First reported case of sulfonamide-associated uveitis and Stevens-Johnson syndrome in a horse
- •Four-year-old Quarter Horse mare developed bilateral anterior uveitis and facial edema following trimethoprim-sulfadiazine treatment for respiratory infection
- •Periorbital skin, muzzle, and vulva began to slough on day five of treatment, revealing nonpigmented underlying skin
- •Acinetobacter johnsonii was cultured from tracheal wash, but clinical signs resolved with cephalosporin therapy and discontinuation of sulfonamide