Effect of an anti-inflammatory dose of prednisone on thyroid hormone monitoring in hypothyroid dogs.

It is not uncommon for a hypothyroid dog to be receiving concurrent corticosteroids. As hypothyroid dogs receiving thyroid supplement need periodic monitoring, knowledge of whether prednisone alters thyroid hormone concentrations would be useful to determine whether testing can or should be done while the dog is receiving therapy and whether dose adjustments are appropriate. In this study, the effect of short-term anti-inflammatory prednisone was determined in dogs with naturally occurring hypothyroidism. Eight adult dogs were given prednisone (1.0 mg/kg, orally) daily for 7 days and then on alternate days for 14 days. Serum total thyroxine (T(4) ), free T(4) (fT(4) ), and thyroid-stimulating hormone (TSH) were measured on days 7, 21 and 28 and compared with baseline data. Total T(4) concentrations were significantly decreased after 7 days of anti-inflammatory prednisone, but were not significantly altered from baseline on days 21 or 28. Free T(4) and TSH concentrations were not significantly altered from baseline at any point during the study. Two dogs had decreased total T(4) concentrations on day 7, which may have resulted in an alteration in thyroid supplementation. Results showed that administration of prednisone at a dosage of 1 mg/kg, orally, once daily for 7 days decreased total T(4) , while fT(4) was unchanged, suggesting that fT(4) may be less affected by daily prednisone administration. Anti-inflammatory doses of prednisone administered every other day did not interfere with thyroid hormone monitoring.