Effects of trimethoprim–sulfadiazine on tear production and the fluctuations of Schirmer tear test values in horses

Abstract

The objectives of this study were to observe the effects of trimethoprim-sulfadiazine on equine tear production and to determine normal fluctuations in Schirmer tear test (STT) values in horses. A randomized, placebo-controlled, blinded clinical trial measuring STT values in 15 horses over an 8-week period was performed. The treatment group (eight horses) received 30 mg/kg trimethoprim-sulfadiazine orally once a day and the control group (seven horses) received placebo (flour) at the same time. All horses were housed outdoors throughout the study. Schirmer tear test values were measured at 0, 2, 4, 6 and 8 weeks, and 4 weeks after discontinuation of treatment. There were no significant differences in tear production between the treated and control groups. Fluctuations in STT were observed and may result from individual and environmental variations. Trimethoprim-sulfadiazine did not decrease tear production in the horses in this study. Horses normally experience periodic fluctuations in STT values.

Effects of short‐term oral administration of trimethoprim‐sulfamethoxazole on tear production in clinically normal Syrian hamsters

“…Although tear production decreased in study population, no clinical signs of corneal or conjunctival inflammation were observed during the study. The results of this study are in agreement with previous studies in rabbit and dog, but are in contrast with the administration of systemic sulfonamides in horse that had no effect on tear production …”

Results of the Schirmer tear test performed with open and closed eyes in clinically normal horses

“…Several factors influence the STT results such as inconsistencies in the absorptive capacities of STT strips due to differences in filter papers, the person performing the test, and the location of strip placement within the conjunctival sac [3]. …”

“…The STT values can also vary depending on inconsistencies in the absorptive capacities of the STT strips due to differences in filter papers or the individual performing the test [3]. …”

Effects of oral administration of trimethoprim‐sulfamethoxazole on tear production in clinically normal guinea pigs

“…Seven days after the end of the trial (Day 21), tear secretion returned to the pretreatment baseline levels in the treatment group. The results of this study were in contrast with the previous studies on rabbits, dogs, and hamsters, but they are consistent with the administration of systemic sulfonamides in horses that had no effect on tear production . During the pretreatment period, the pretreatment baseline PRTT values for all the guinea pigs were established to be within the reference range reported in normal guinea pigs (6.8–25.2 mm/15 s) .…”