L-levothyroxine therapeutic dosage evaluation in dogs with primary hypothyroidism

Viviani De Marco Roberta M.T. Silva Mariana A. Karamm Jorge C. Florio Carla A.B. Lorigrados About the authors

The acquired primary hypothyroidism is a frequently diagnosed endocrinopathy in dogs. The therapy constitutes in oral supplementation with sodium levothyroxine (L-thyroxine), however various therapeutic protocols have been proposed in the literature, with doses ranging from11 to 44mg/kg once or twice a day, since L-thyroxine has a great variability of absorption and plasma half life. We studied 30 dogs with primary hypothyroidism (13 males and 17 females, mean age 7.9±1.9 years and mean weight of 19.1±12.6 kg), in order to evaluate the dose and frequency of administration of L-thyroxine used more often able to secure a satisfactory therapeutic control as measured by clinical signs and test post-pill, and to correlate the amount of thyroxine employed with the animals' weight. The mean dose of thyroxine used in our study was 16.9±3.1mg/kg, and the frequency of administration every 12 hours in 50% of cases. To investigate a possible correlation between weight and dose of thyroxine used, since small dogs have a higher metabolic rate than large dogs, the animals were grouped in Group A, dogs weighing <10 kg (n=12/30, 7.7±2.1 kg) and group B, dogs weighing> 10 kg (n=18/30, 26.8±10.7 kg). The mean dose of thyroxine used in groups A and B did not differ significantly and were respectively 16±3mg/kg and 17±3mg/kg. The frequency of administration was 50% every 24 hours and 50% every 12 hours for both groups. Thus, the dose of thyroxine does not seem to correlate with the weight of the animal being unpredictable who should receive the highest dose and frequency of the medication. The protocol should be individualized and the patient adequately monitored.

Primary hypothyroidism; L-thyroxine; therapy; dogs

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