Can you discuss initiating and sequencing thyroid hormone replacement—how you monitor patients, guideline-directed therapy, and the importance of metabolic and patient-centric factors in determining when DTE therapy should be considered?
So once somebody is diagnosed with hypothyroidism and are shown to require thyroid replacement medicine, um, the typical initial um treatment to use is the levothyroxine or LT4 monotherapy. Um, again, that could be Synthroid name brand, that could be levothyroxine generic, that could be Unithroid. And the way that we determine what to use typically depends on if the patient's tried one of the formulations and done well or not, um, or if they, a lot of it has to do with insurance coverage. Um, the levothyroxine generic. has different manufacturers. So when we talk about putting patients on that treatment, we always remind them that they should talk to their pharmacist about who the manufacturer of the product is and to monitor their symptoms and their labs if that manufacturer ever changes. Many times pharmacies get deals with certain manufacturers and then they change based on those deals, and that can have a catastrophic effect on somebody's well-being who's on this medicine can also significantly impact their thyroid levels and the way that their body metabolizes the thyroid medicine. So if a patient doesn't want to worry about their pharmacy changing manufacturers every so often, they might elect to go on a um uh uh like a Synthroid or a name brand prescription that doesn't change. Also considerations when somebody is going on levothyroxine therapy is um whether or not somebody has a dye intolerance. So all of these excipients um have potential side effects as well. The most common is headache in patients who have a dye intolerance. Um, so, in that case, Synthroid or levothyroxine 50 mcg, which is a dye-free, um, pill, and trying to kind of formulate the dose based on the 50 mcg tablet or going to something that is dye-free like tiresin or tiresin solution might be the answer. Um, the way that those patients are monitored is that they would get on a medication and then they would have their thyroid levels done at least 4 weeks later. It takes some time for TSH to normalize, um, but sometimes up to 12 weeks depending on availability of the clinician and how the patient is doing. In pregnancy and in other times, a lot of times we will monitor levels more frequently, um, every 4 to 6 weeks typically, um, because it's very important to get that TSH under good control in, um, early pregnancy. And so, um, the guidelines say to monitor a TSH and then to reflex a free T4 if the TSH is abnormal. In my clinical practice, when I have somebody on any type of thyroid medication, I want to know not just what the pituitary is seeing, that's what the TSH is, um, but also is the T4 getting into the body? So that's a free T4 level. Sometimes people have absorption issues in the small intestine and they can't break down their tablet consistently or they're missing doses. And that free T4 will tell me, are they getting the medication correctly and is it absorbing consistently? And then, um, we will check free T3 levels. So free T3 is the active form of thyroid hormone, and that is to determine whether or not this individual person in front of me is taking that medication and doing what the body is theoretically supposed to do, which is take it and convert it to active thyroid hormone. Some people do that beautifully. Many times it is younger patients who don't have a lot of medical comorbidities or patients who have good muscle mass and good enzymatic activity and conversion. But there are patients who are on medications that inhibit conversion like beta blockers or steroids for inhaled steroids, steroids of any kind. Um, or patients who have inflammation going on, osteoarthritis or diabetes or other comorbidities that impair their ability to take the T4 monotherapy and make T3. I also personally checked a reverse T3. Um, I think it is beneficial in figuring out how the body is metabolizing the medication. Reverse T3 is inert thyroid hormone, and by looking at that, it helps me to understand how to dose a a medication with a patient if we have to switch to something like T4-T3 combination therapy or DTE. If somebody is taking T4 monotherapy and they've normalized their TSH, they've normalized their free T4, but their free T3 is lower, low normal and their reverse T3 is high, higher than I want. At that point, many times the patient will still be complaining about hypothyroid symptoms despite a normal TSH. And those are the patients that we would start thinking about T4-T3 combination therapy with, um, either adding Cytomel and adjusting the T4 treatment or, um, switching to DTE products which have the T4-T3 combination already in the tablet. And so with those medications, typically you have to think about um when in the dosing cycle you're checking labs. Um, so unlike T4 monotherapy, which is very steady state once it enters the bloodstream, it has a pretty long half-life. You don't have to really worry about peaks and troughs and when they last took their medication. When you go on something like liothyronine or when you go on DTE products, they have a peak and a trough. Usually they peak within 1 to 2 hours of taking the medication, though that's variable with the patient. And so when we're looking at labs, we always want to ask the patient, When did you last take your thyroid medicine so that we can interpret the TSH, the free T4, the free T3, and the reverse T3 correctly. Many times in my clinical practice, I will check at a nadir, a low point. So I will ask them to not take their medication the morning of the labs so that I can see what the low point looks like and make sure that the medicine is lasting for them. Um, sometimes I want to look at a peak of medication, especially if they have side effects like heart palpitations or jitteriness or hyperthyroid symptoms, suggesting that the medicine might be peaking too strongly. Um, but typically, we are always asking when they last took their medication and using that to interpret the medicine or to interpret the labs.
