Thyroxine replacement therapy is given in hypothyroidism or underactive thyroid. Dose of the thyroxine is determined by various factors such as age of the patient, severity of the condition, how long the disease is present, and so on.
But it is vital to check if the thyroxine replacement therapy is adequate or not. The main motto of the treatment is to treat hypothyroidism. When the thyroxine replacement therapy is more than needed, then hyperthyroidism symptoms can develop. Similarly, when the thyroxine replacement therapy is less than needed, then hypothyroidism symptoms can develop.
So, proper replacement therapy with thyroxine is a must. Under treatment or over treatment, both can cause health issues. So, what things to consider in thyroxine replacement therapy? Let’s have a look.
Factors Causing Under Replacement Of Thyroxine
The following factors contribute to the under replacement of thyroxine therapy. As a result, the dose of thyroxine is inadequate for the body. Thus, symptoms of hypothyroidism persists due to inadequate dose of thyroxine. The factors are
Inadequate Prescribed Dose
If the prescribed dose of thyroxine is inadequate to meet the body’s requirement, then symptoms of hypothyroidism will persist. Inadequate dose does not fulfill the motto of treatment of hypothyroidism. As a result, various vital functions of the body will be compromised.
Limited Compliance
Non adherence to prescribed medicine is a common cause of under replacement of thyroxine therapy. Skipping of medicine, taking reducing amount of thyroxine dose, etc. cause inadequate therapy. Thus, symptoms of hypothyroidism will persist.
Decreased Absorption
Decreased absorption of thyroxine due to the ingestion of the following agents that bind thyroxine can cause under replacement of thyroxine therapy. Due to the decreased absorption, despite taking the right dose of thyroxine, body will not get adequate thyroxine. As a result, hypothyroidism will persist. The agents are the following
- Ferrous sulfate
- Calcium carbonate
- Aluminum hydroxide
- Sucralfate
- Cholestyramine
- Soy protein
Increased Metabolism Of Thyroxine
When there is increased metabolism of thyroxine, then the desired dose of thyroxine will be less inside body. So, hypothyroidism can still persist. The following factors can cause increased metabolism of thyroxine
Pregnancy
During pregnancy the metabolism of thyroxine is increased. As a result, body gets inadequate dose of thyroxine despite taking the prescribed dose of thyroxine.
Drugs
Drugs can cause increased metabolism of thyroxine, so body gets inadequate dose of thyroxine. As a result, symptoms of hypothyroidism can persist. If you are taking the following drugs along with thyroxine replacement therapy, you should mention to your doctor so that the right dose of thyroxine based on your other ongoing drug therapy can be prescribed. The drugs that increase the metabolism of thyroxine are the following
- Phenytoin
- Phenobarbital
- Carbamazepine
- Rifampin
Diminishing Residual Thyroid Function
Thyroxine replacement therapy is given based on the severity of hypothyroidism. Sometime it is seen that the thyroid gland function deteriorate with time due to various reasons. When this happens, the prescribed dose of thyroxine become inadequate to fulfill the body needs. So it is vital to do follow up during thyroxine replacement therapy.
Changing Thyroxine Formulations
Changing the thyroxine formulations can cause under replacement of thyroxine therapy. The absorption of different formulations vary. Not only that, the overall availability of the thyroxine in the blood after absorption can vary as much as 12 percent. So taking a single, consistently identifiable thyroxine formulation is very important. For this, always take the same generic or brand name formulation.
Factors Causing Over Replacement Of Thyroxine
When there is decreased need of thyroxine and one is taking over dose, then it is called over replacement of thyroxine. As a result, symptoms of hyperthyroidism will develop. Taking over dose of thyroxine is fatal to our body. One should always take the right dose that is adequate to maintain normal vital functioning of our body. The factors that can cause over replacement of thyroxine are the following
Excessive Prescribed Dose
Excessive prescribed dose of thyroxine can cause over replacement of thyroxine. It can occur if the laboratory test results of TSH, T3, T4 are inaccurate. It can also occur if with time thyroid functioning of the patient improves.
Factitious Ingestion Of Additional Doses
Factitious ingestion of additional thyroxine doses cause over replacement of thyroxine. Taking over dose of thyroxine is dangerous, especially when it is self imposed by the patient. When the patient takes over dose of thyroxine intentionally, the over dose can not be predicted and can be highly fatal within a short time. So it is vital to monitor drug dose by the family members. The aim is not to take additional dose. One should always take the prescribed dose.
Decreased Metabolism Of Thyroxine
Decreased metabolism of thyroxine by the body can cause the thyroxine to stay in the blood for more time. As a result, despite taking the prescribed dose of thyroxine, it can cause increased concentration of thyroxine in the blood due to decreased metabolism. Decreased metabolism of thyroxine is particularly seen with aging. So, elderly people needs more follow up than the younger people to determine the appropriate thyroxine dose with time.
Increasing Residual Thyroid Function
When the residual thyroid function improves, the required thyroxine dose is reduced. But if the patient still takes the previous dose, it leads to over dose of thyroxine. So, it is vital to go for follow up during thyroxine replacement therapy. Taking the right dose of thyroxine as per body needs is always essential.
Changing The Thyroxine Formulation
One should always take the same formulation of thyroxine. As different formulations of thyroxine have different absorption rate in our body, so it is essential to take the same generic or brand formulation of thyroxine.
Takeaway
Thyroxine replacement therapy is needed when our thyroid gland can not produce enough thyroid hormone as per body needs. So to maintain normal body functioning, replacement therapy with thyroxine is started. As various factors can cause under replacement or over replacement of thyroxine inside our body, so follow up is highly important during the therapy.
Also, tell your doctor if you are taking any additional drugs, supplements, herbal products, etc. because many of these agents can cause change of thyroid hormone concentration in the blood. Taking the right dose of thyroxine as per body needs is important. The need of thyroxine replacement can increase or decrease with time. When the need of thyroxine replacement therapy decreases, it simply means that your thyroid functioning is improving and vice versa.
So, always consult with your doctor if during thyroxine replacement therapy, you feel additional issues. Overdose of thyroxine can cause hyperthyroidism. Similarly inadequate dose of thyroxine can cause hypothyroidism. Never hesitate to consult with your doctor about your thyroid issues. Stay healthy and happy.
