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Article
Effects of Short-term Trimethoprim-sulfamethoxazole Administration on Thyroid Function in Dogs
Journal of the American Veterinary Medical Association (2002)
  • Nicola L. Williamson, University of Tennessee - Knoxville
  • Linda Frank, University of Tennessee - Knoxville
  • Keith A. Hnilica, University of Tennessee - Knoxville
Abstract
Objective—To determine how rapidly trimethoprimsulfamethoxazole affects serum total thyroxine (T4) and thyroid-stimulating hormone (TSH) concentrations in euthyroid dogs and how quickly hormone concentrations return to reference values following discontinuation of administration. Design—Prospective study. Animals—7 healthy euthyroid dogs. Procedure—Dogs were given trimethoprim-sulfamethoxazole (26.5 to 31.3 mg/kg [12 to 14.2 mg/lb], PO, q 12 h) for a maximum of 6 weeks. A CBC and Schirmer tear test were performed and serum total T4 and TSH concentrations were measured weekly. Administration of trimethoprim-sulfamethoxazole was discontinued if total T4 concentration was less than the lower reference limit and TSH concentration was greater than the upper reference limit or if persistent neutropenia developed. Results—Six dogs had total T4 concentrations less than the lower reference limit within 3 weeks; T4 concentration was decreased after 1 week in 3 of these 6 dogs. In these 6 dogs, TSH concentration was greater than the upper reference limit within 4 weeks. In 1 dog, T4 and TSH concentrations were not affected, despite administration of trimethoprimsulfamethoxazole for 6 weeks. Neutropenia developed in 4 dogs. In 1 dog, the neutropenia resolved while trimethoprim-sulfamethoxazole was still being administered. In the other 3, neutrophil counts returned to reference values 1 week after drug administration was discontinued. Conclusions and Clinical Relevance—Results suggest that administration of trimethoprim-sulfamethoxazole at a dosage of 26.5 to 31.3 mg/kg, PO, every 12 hours can substantially alter serum total T4 and TSH concentrations and neutrophil counts in dogs within as short a time as a few weeks.
Publication Date
September 15, 2002
Citation Information
Nicola L. Williamson, Linda Frank and Keith A. Hnilica. "Effects of Short-term Trimethoprim-sulfamethoxazole Administration on Thyroid Function in Dogs" Journal of the American Veterinary Medical Association Vol. 221 Iss. 6 (2002)
Available at: http://works.bepress.com/linda_frank/33/