Frankel, G, Kusno, A, Louizos, C. Five things every community pharmacist should know when dispensing for 4-legged patients. Can Pharm J (Ott) 2016;149:99-106. doi:10.1177/1715163516628543.
In the initial OnlineFirst version of this article published on February 5, 2016, due to a conversion error, levothyroxine dosages appeared as milligrams (mg) instead of micrograms (µg) in the “Canine levothyroxine prescriptions” section. The corrected paragraph is as follows:
“There are several reasons why levothyroxine dosages are much higher for canines. First, dogs have higher daily requirements for thyroid hormone than humans, because of their physiology. Dogs secrete approximately 8 µg /kg/d of thyroxine (T4) from their thyroid gland compared with approximately 80 µg /d (1.2 µg /kg/d) for an average 70 kg human.24,25 Second, levothyroxine is more poorly absorbed by canines than humans. Canine oral bioavailability for levothyroxine varies from 10% to 50%.24 Human bioavailability for levothyroxine ranges from 64% to 81%.26 Finally, levothyroxine half-life is much shorter in dogs compared with humans. Half-life can vary between dogs, but the accepted range is approximately 8 to 16 hours. In humans, the levothyroxine half-life is much longer, between 144 and 192 hours (6-8 days). Higher per-kilogram daily requirements of T4, lower oral bioavailability and short half-life all contribute to higher canine levothyroxine dosage requirements. The initial dose of levothyroxine for canines is 20 µg /kg of body weight twice daily.27 It is not unusual to see levothyroxine prescriptions for up to 800 µg twice daily (recommended maximum dose) depending on the animals’ weight. To illustrate, a 16 kg cocker spaniel would require 320 µg twice daily for appropriate thyroid replacement therapy.”
The correct dosages are updated in the latest online version, including the printed issue.