Suspect novel adverse drug reactions to trimethoprim‐sulphonamide combinations in horses: A case series

Abstract

Adverse drug reactions to trimethoprim-sulphonamide combinations are common in many species, manifesting as gastrointestinal tract disorders, dermatopathies and blood dyscrasias. In this case series, neurological abnormalities in 4 horses being treated with trimethoprim-sulphonamide combinations at normal dosages and in one foal that received an overdose are described. The horses developed hypermetric gait, agitation and erratic behaviour. All signs resolved once medication was withdrawn, and no horse had residual deficits. No other cause for observed neurological deficits could be determined. These clinical signs appear to represent a novel adverse drug reaction to some commonly used antimicrobial combinations.

Pancytopenia in two horses following administration of potentiated sulfonamide antimicrobials

“…The potentiated sulfonamides can have potentially life threatening side effects; trimethoprimsulfamethoxoazole and sulfadiazine-pyrimethamine combinations have been associated with the development of immune mediated disease and aplastic anaemia in dogs (Trepanier 2004), horses (Thomas and Livesey 1998;Toribio et al 1998;Piercy 2002) and man (Cribb 1996). Other reported adverse effects to potentiated sulfonamide antimicrobials in horses include diarrhoea (Ensink 1996) and neurological deficits (Stack and Schott 2011). This report describes 2 cases of pancytopenia mediated by different mechanisms following administration of a commonly used potentiated sulfonamide.…”

“…; Piercy ) and man (Cribb ). Other reported adverse effects to potentiated sulfonamide antimicrobials in horses include diarrhoea (Ensink ) and neurological deficits (Stack and Schott ). This report describes 2 cases of pancytopenia mediated by different mechanisms following administration of a commonly used potentiated sulfonamide.…”

“…The antimicrobial drug combination of a sulfonamide and a diaminopyrimidine, is used commonly in equine practice (Stack and Schott ). A number of sulfonamide‐diaminopyrimidine combinations exist including trimethoprim‐sulfadimidine, trimethoprim‐sulfamethoxazole, trimethoprim‐sulfadiazine and trimethoprim‐sulfadoxine.…”

Pancytopenia in horses

“…Reports of adversity to sulfonamides in horses is limited. One report by Stack and Schott () describes adversities that were primarily neurological in manifestation. The onset of clinical signs in 3 of the 4 horses was 2 days or less, suggesting a different (non‐allergic) mechanism of adversity.…”