Antithyroid medications are used to treat an overactive thyroid gland (also know as hyperthyroidism). When the thyroid gland is overactive, it makes too much thyroxine (also known as T4). The extra thyroxine can accelerate the metabolism rate of your body. As a result, it can cause weight loss and irregular heart activity.
Therefore, antithyroid medications (which includes methimazole and propylithiouracil) are used to reduce the amount of hormone (T4) released by the thyroid gland. These drugs does not affect the thyroxine which is already made, but reduce the further production. Therefore, it may take four to eight weeks of treatment for your thyroxine level to come down to normal.
Antithyroid Drugs during pregnancy
If you take antithyroid drugs, you should discuss your treatment with your doctor before becoming pregnant:
- Methimazole: Using methimazole during pregnancy could harm the unborn baby. Tell your doctor if you are pregnant or if you become pregnant while using this medicine.
Methimazole can pass into breast milk and may harm a nursing baby. Ask your doctor about any risk.
- Propylthiouracil: Do not use propylthiouracil if you are pregnant. Tell your doctor right away, if you become pregnant. This medicine can harm an unborn baby, or cause serious liver problems or death of the baby or the mother. You may need to use another medication during late pregnancy.
It may not be safe to breast-feed while using propylthiouracil. Ask your doctor about any risk.
Side Effects of Antithyroid medications?
You may require careful monitoring to get the right levels of these medicines for you. However, when taking an antithyroid medicine, if you develop any of the side-effects (listed below) or any other signs of infection, you must stop the medicine and report this to your doctor immediately.
- Mild stomach upset
- Painful joints
The above side-effects are usually not serious and often go, even if you continue with the medication.
But in rare cases, antithyroid medicine can cause a serious side-effect on the blood-making cells. This can drastically reduce the number of blood cells in your body, including the cells that fight off infection and those that help to stop bleeding.
There’s also the risk of liver damage. Therefore, see your doctor right away if you develop following symptoms, while taking these drugs.
- A sore throat.
- Mouth ulcers.
- Unexplained bruising or bleeding.
- Jaundice (yellowing of the skin and eyes)
- Any other signs of infection.