The characteristics of T3 and T4 and their clinical applications; the thyroid gland synthesizes a mixture of T3 and T4, and we also mix them in proportion to each other when supplementing. Patients ask you: I forgot to take my medication, what should I do? When is the most reasonable time to take it? What should I pay attention to when taking the medication? How often should I be reviewed to adjust my medication? After reading this section, you will find the answers: 1. The discovery of thyroxine dates back to the late nineteenth century, before people associated mucinous edema, cretinism and the thyroid gland. in September 1883, Sir Felix Semon, an internist, announced to the London Medical Society that these pathological conditions were caused by an underactive thyroid gland. imagine the sensation! The definitive proof came eight years later when George Redmayne Murray first reported that an extract (injection) of the sheep thyroid gland had successfully cured a 46-year-old patient with mucinous edema, who thereafter survived in good health for 28 years. At the time, this was explosive and incredible news, and a year later, Hector Mackenzie and Edward Lawrence Fox each reported on the use of oral thyroid preparations. Since then, dry thyroid preparations have been used and continued to be used for several decades. In fact, levothyroxine (which is what we call T4, not “levothyroxine”) was synthesized as early as 1927, but it was so expensive that people could rarely afford it before the 1860s. Then, triiodothyronine (what we call T3), T4 and their mixtures became popular. Considering that the thyroid gland synthesizes both of these hormones, it seemed reasonable to mix the two into tablets. This concept was not abandoned until the 1870s. Because researchers discovered that the vast majority of T3 in the body, is converted from T4, it took more than 30 years after that for T4 to officially enter the history books as a separate dosage form. T4, which we call levothyroxine (not “levothyroxine”, Chinese name: 禹甲乐), provides all the thyroxine you need to be healthy and happy. When it is not produced enough, we feel sick all over. If it is completely interrupted, it is estimated that the body will survive for a few months. Next we look at its characteristics in order to benefit from it to the fullest extent. In North America, T4 is the second most prescribed drug. It is not simpler than aspirin, but it is also not as complicated as chemotherapy drugs. small changes in T4 will be amplified in the body due to the extreme sensitivity of TSH. For this reason, we recommend that patients stick with the same brand of T4. of course, T4 works within a certain range, so even a change in brand is not likely to cause significant discomfort to the patient. How do I take T4? The best way is to take it early in the morning on an empty stomach and to stick to it daily. If you forget to take your medication in the morning, refill it as soon as you remember. If you take the medicine on a full stomach, the food will slightly interfere with the absorption of T4. So it is best to take some time between taking the medication and using breakfast (lvygwyt note: the instructions for Umethazine recommend at least 30 minutes for this reason), and avoid soy preparations because they can affect the absorption of T4 in the intestine. Remember to take the dose on time to keep the TSH at the desired level. t4 will be fully absorbed within 5 hours, the majority within 3 hours. Some medications, such as iron, can interfere with absorption and are recommended to be taken after 4 hours; calcium should be used after 1 hour; aluminum thioglycollate, colestipol, and magnesium hydroxide should all be taken after 4-5 hours. T3 is the active form of thyroxine and accounts for 10-20% of total thyroxine. The vast majority of T3 needed by the body is converted from T4 and is capable of performing all the functions of thyroxine. If you are taking T4, the body will have some control at the conversion stage (enzymes that control the conversion of T4 to T3), and knowing this, you can understand why T4 is recommended in most cases. So when do you use T3? This is going to take some more padding. The half-life of T4 is one week, while T3 is one day. That means that one week after stopping T4, the T4 level in the body is still 50% of the baseline level, after two weeks it is 25%, after three weeks 12.5%, after four weeks 6%, after five weeks 3%, and after six weeks about 1%. This is the reason why patients taking T4 (such as eugenol) should be reviewed once every six weeks (lvygwyt note). Similarly, the half-life of T3 is only one day. This creates a lot of favorable and unfavorable points. The advantage of T4 is that when you get the dose adjusted, the concentration in the blood remains relatively stable. The disadvantage is that if you stop the drug, it takes up to six weeks for low A to manifest (for example, to get TSH up above 30 when you have to do 131I therapy, or a nuclear scan.) The advantage of T3 is that in the same situation, a short stop will bring TSH up (patients avoid being in a high TSH state for a long time, which can lead to the risk of cancer recurrence, lvygwyt note). Well, we stop T4, switch to T3 for the first four weeks to avoid high TSH, and then stop T3 as well for the next two weeks, and TSH will rise rapidly. It is at this point that a nuclear scan or measurement of thyroglobulin will be accurate and effective. For the same reason, T3 is not routinely recommended for patients on T4 (e.g., patients with low thyroid after nail cancer surgery), and it takes six weeks of medication to reach baseline levels. This is because the patient will experience mild hypo and mild hyperthyroidism in one day. Ideally, it would be nice to have an extended-release dosage form. Unfortunately, so far, no such ideal medication is available either. Another disadvantage of using T3 is that it bypasses the physiological state that is converted from T4. It has been shown that T4 crosses the blood-brain barrier more easily than T3, and that nerve cells “prefer” T3 converted from T4. A mixture of T3 and T4, either artificial or animal-derived, has been shown to be unreasonable. Artificial formulations: mixing T3 and T4 in proportion to each other in the hope that they would behave as they do in the physiological state, but this “dream” was ultimately dashed. The body secretes the required amount of thyroxine continuously and steadily, and when mixed, it is all absorbed within 3 hours, resulting in rapid peaks and valleys (short T3 half-life), which is far from the physiological state. Dried thyroid preparations for animals used to be the main drug half a century ago. But these drugs contain many kinds of hormones and compounds in the thyroid, including T3, T4, thyroglobulin, and derivatives of T3 and T4 deiodination. And the only means of detection is to look at its iodine content, which is almost POOR, and it is difficult to ensure a constant dose between one batch and another, or even the same batch of drugs. Many advanced tests have been tried and the results are the same. Thyroxine (tablets)? Does anyone still use it? We all use euthyroxine now. Thyroxine tablets are a mixture of T3 and T4, extracted from the thyroid gland of animals such as pigs, and the content is not constant; Eugenol is a single T4 with constant content, and it is easy to break into 1/2 or 1/4; in addition, T4 is converted into T3 when the body needs it to work, and it is less likely to cause hyperthyroidism than direct T3 supplementation. This is the reason why eugenol is now replacing thyroxine tablets.