Hypothyroid dogs sometimes require prednisone treatment for concurrent diseases, including allergic skin diseases. Sustained monitoring of thyroid function is required to assess the effects of short-term prednisone therapy on thyroid hormone concentrations. In this study, 8 dogs with spontaneously occurring hypothyroidism (undergoing replacement therapy) received 1 mg/kg oral prednisone Q 24 H for 7 days; then every other day for 14 days. Serum for total thyroxine (T4), free thyroxine (fT4), and thyroid stimulating hormone (TSH) concentrations were collected at baseline and approximately 6 hours posttreatment on days 7, 21, and 28.

Mean serum T4 concentrations were significantly decreased on day 7 compared with baseline concentrations, but were not significantly different from baseline on days 21 or 28. FT4 and TSH concentrations were not significantly different between baseline and any posttreatment test periods. Decreased T4 concentrations were identified in 2 dogs on day 7. Prednisone administration (1 mg/kg PO Q 24 H for 7 days) decreased T4, although fT4 was unchanged. This suggested that fT4 concentrations were less susceptible to daily prednisone administration. Alternate-day prednisone dosing did not interfere with thyroid hormone monitoring.

Commentary: Many dog breeds are predisposed to both allergic skin disease and hypothyroidism. Both conditions can be controlled (not cured); however, concurrent monitoring of both can be difficult. Hypothyroidism requires daily lifelong supplementation with routine monitoring. Conversely, many variables determine the therapeutic type, length, and drugs used to provide antipruritic relief to allergic dogs. It is preferable to avoid adjustment of thyroid hormone supplementation in allergic dogs treated with prednisone; however, this is not always possible. Results from this study suggested that short-term prednisone had the greatest impact on T4 at day 7 after administration; there were no significant differences between baseline values and values from days 21 and 28. These results suggest that testing should be performed when the dog is receiving the lowest dose of alternate-day prednisone therapy. Future studies should evaluate larger canine populations.—Karen A. Moriello, DVM, Diplomate ACVD

Effect of an anti-inflammatory dose of prednisone on thyroid hormone monitoring in hypothyroid dogs. O’Neill SH, Frank LA, Reynolds LM. VET DERMATOL doi: 10.1111/j.1365-3164.2010.00932.x