Single Dose T3 Administration: Kinetics and Effects on Biochemical and Physiologic Parameters

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.

doi: 10.1097/FTD.0000000000000113

PMCID: PMC5167556

NIHMSID: NIHMS835764

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

Abstract

Background

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.

Methods

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.

Results

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.

Conclusions

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:

ncbi.nlm.nih.gov/pmc/articl...

6 Replies

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  • Thank you for posting. I love having such specific details like this...it just gives me so much more confidence about managing my health and advocating for myself.

  • Thank you so much helvella . I will be printing this one for my files and next time I tell my endo I take my T3 as a single daily dose between 4 and 6am and he raises his eyebrows at me I can ignore him with confidence.

  • Thanks for very informative link and it's good to have a scientific reason rather than 'assumptions' about the role of T3. I am never aware of a 'peak' although it must do.

  • That is fascinating information - I never notice any peak with the NDT but perhaps it explains why due to my worst lapses of memory I miss or have a delayed dose I seem completely unaffected and can go on with everything quite easily. I felt wretched on T4 even after 2 years (if I took more I started to go hyper) so assume it is the T3 in NDT that made all the difference. Mmm this thyroid stuff is not simple at all. There is a lot more unknown than known.

  • I'm not sure I fully comprehend the meaning of the article 😏

    I self medicate with 2 x25 mcg T3, but would like to switch to a single dosage of 50 mcg, as I have difficulty remembering my afternoon dosage in the right time according to food.

    But I'm afraid of having a hyper reaction if I take 50 mcg at once. On two dosages of 25 mcg I sometimes feel a transient peak after 2.5- 3 hours, of strong heartbeats, but heart rate rarely above approximately 84.

    Should I give it a try ??? 😬

    I hope soon to get a prescription of NDT by an endo I have been referred to, as I've had much better effect of that some years ago (self medicated Raw Thyroid, but alas! got too expensive)

    Please give me some encouraging advice 💗

  • I'll leave those who actually take T3 to answer! I find papers but don't have the personal experience. :-)

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