Levothyroxine Pharmacology – RLP Episode 007

Real Life Pharmacology - Pharmacology Education for Health Care Professionals

Eric Christianson, PharmD; Pharmacology Expert and Clinical Pharmacist

Education, Health & Fitness, Medicine

5 • 716 Ratings

🗓️ 22 March 2018

⏱️ 9 minutes

🔗️ Recording | iTunes | RSS

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Summary

In this episode, I talk about levothyroxine pharmacology and how it is one of the most commonly prescribed medications. Levothyroxine gets converted from T4 to T3 in the body.

I also talk about some of the side effects that are encountered if we oversupplement as well as what we look for as far as lab work goes.

Drug interactions are important with levothyroxine and I do discuss this as well as mention a couple of really common medications that can cause issues with thyroid hormone.

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Transcript

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0:00.0	Lebothyroxin is one of the most common used medications.
0:05.0	I believe it's in the top 10 or top 20, most commonly prescribed meds.
0:11.0	And this medication is simply used for hypothyroidism.
0:17.0	As far as its mechanism of action goes,
0:27.8	Levothyroxin, the pill itself, is synthetic T4 hormone,
0:34.7	and in the body that's actually converted to active T3.
0:45.1	And like I mentioned, it's for replacement of thyroid hormone. Patients with hypothyroidism will generally present with lack of energy, fatigue, possible weight gain, hair loss I've seen, maybe a coldness in the extremities like the hands
0:59.0	and the feet. And from those symptoms, we'll oftentimes check a TSA and that hypothyroidism is
1:08.0	diagnosed generally by T.S.H.
1:12.0	Now, T.S.H is thyroid-stimulating hormone.
1:16.1	And so here's where it gets a little tricky.
1:19.1	When we think about dosing of levothyroxin, it's counterintuitive to the level of the TSA.
1:30.3	It's going to be the opposite.
1:32.3	So if your T.S.H.
1:33.3	That's telling your body that we need to produce more active thyroid hormone.
1:42.3	When T.S.H. is low, that's telling your body, whoa, tone it back a little bit,
1:49.6	and don't produce as much thyroid hormone. So in hypothyroidism, generally what you're going to see
1:57.1	is an elevated TSA. Now there are a few exceptions to that, which I'm not going to go into
2:03.4	great detail here, but remember elevated thyroid stimulating hormone or TSA. That's going to
2:12.6	lead you to generally initiate levothyroxin and or increase. Now with that I did want to add the usual
2:24.0	TSA range is in the ballpark of 0.5 to 5 so that's kind of the normal range might
2:31.2	depend a little bit on your lab of course but that's kind of a
	...

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