As so many times said here, T3 (liothyronine) has an impact that lasts far longer than the so-called "half-life" would seem to suggest (if that helf-life is taken naively as indicating how long the effects continue).
Also, as so many times said here, identifies the impact of T3 on TSH...
Published in final edited form as:
Ther Drug Monit. 2015 Feb; 37(1): 110–118.
Single Dose T3 Administration: Kinetics and Effects on Biochemical and Physiologic Parameters
Jacqueline Jonklaas, MD, PhD,1,* Kenneth D. Burman, MD,2 Hong Wang, MD,3 and Keith R. Latham, PhD4
1Division of Endocrinology, Georgetown University Medical Center, Washington, DC
2Endocrine Section, Washington Hospital Center, Washington, DC
3Medstar Health Research Institute, Hyattsville, Maryland
4IPE Inc, Kingsport, TN
*Address all correspondence and requests for reprints to: Jacqueline Jonklaas, Division of Endocrinology, Georgetown University, Suite 230, Bldg. D, 4000 Reservoir Road, NW, Washington, DC 20007. Phone number: 202 687 2818, Fax number: 1 877 485 1479. Email: ude.nwotegroeg.@jaalknoj
As changes in thyroid stimulating hormone, thyroid hormones, and vital signs following administration of a single dose of liothyronine have typically only been documented for 24 hours, we documented these parameters over 96 hours.
Blood samples were obtained for 4 days after administration of 50-mcg liothyronine. Concentrations of total and free triiodothyronine, free and total thyroxine, and thyroid stimulating hormone were measured. Vital signs were documented.
Triiodothyronine concentrations peaked at 2.5 hours following liothyronine administration. Heart rate increased by 5 hours after liothyronine administration, subsequently reaching a value higher than baseline (p value 0.009). Suppression of thyroid stimulating hormone concentrations began at 2 hours. The nadir thyroid stimulating hormone value at 12 hours was significantly different from baseline (p <0.001), and remained lower than baseline for 2–3 days.
A single dose of liothyronine has both short term and longer term effects. There is clearly a different lag time between the serum concentrations of triiodothyronine and its effects on the heart and pituitary respectively. The increase in serum triiodothyronine concentration occurred with hours and was then followed by an increase in heart rate. The increased heart rate was transient and was followed by a reduction in thyroid stimulating hormone concentration. The suppression of thyroid stimulating hormone was delayed, but was more sustained. Thus, sustained thyroid stimulating hormone reduction beyond 24 hours was achieved by a single dose of liothyronine that produced only brief increases in serum triiodothyronine levels and transient increases in heart rate.
Key terms: T3, triiodothyronine, kinetics, TSH, heart rate, temperature
Full paper freely available here: