What is Methimazole?
Methimazole is an antithyroid drug of the class of drugs known as thioamides. It received medical labelling as Tapazole from the US Food and Drug Administration (FDA) in 1950 [1]. Methimazole contains a 5-membered imidazole ring (a methyl group on position 1 and a thione group on position 2) [1].
What Does Methimazole Do?
Methimazole works by mainly reducing thyroid hormone levels in the thyroid gland. It interferes with the enzyme function carried out by thyroid peroxidase, iodinates tyrosine molecules in thyroglobulin, and blocks T4 and T3 thyroid hormones [1]. In impeding this process, methimazole reduces thyroxine (T4) and triiodothyronine (T3), the two main thyroid hormones involved in the regulation of metabolism, growth, and development in humans [1].
Methimazole is used for hyperthyroidism (a depressed thyroid), and also prior to thyroid surgery or radioactive iodine treatment. Methimazole can be used for other uses not covered in this medication guide [2].
Besides being a primary action, methimazole can also be used for disease management by changing the overall behaviour of the immune system. A couple of papers report an overall decrease in immune molecules and a possible relief from immune hyperthyroidism [1].
Risks of Methimazole
The antithyroid drug methimazole has many risks associated with its use.
One of the main risk factors is hepatotoxicity, as seen in:
- Jaundice
- Dark urine
- Abdominal cramping
- Nausea
- Vomiting
- Or other signs of liver disease.
This risk is increased in patients with severe liver disease or impairment because methimazole gets broken down in the liver and can lead to liver damage or liver failure [1].
Acute pancreatitis is another risk factor. Although some research has not found a strong relationship between methimazole use and acute pancreatitis, others suggested an increased risk, especially in the early months of treatment [3, 4, 5].
Methimazole is also hypothyroid so it’s very important to take serum T3 and T4 levels at appropriate times to keep patients euthyroid [1].
Furthermore, methimazole may lead to severe illnesses like vasculitis – the inflammation of blood vessels due to an immune reaction to the medication [1].
Methimazole, too, has been linked to hypoprothrombinemia and risk of bleeding, so prothrombin time must also be monitored in patients prior to surgery [1].
Relationship Between Methimazole and Glucose
Methimazole is an antithyroid drug used mainly to cure hyperthyroidism. It works by inhibiting thyroid hormone secretion from the thyroid gland, which prevents thyroid peroxidase-driven enzyme reaction synthesis of T4 and T3 thyroid hormones [1].
The interactions between methimazole and glucose involve many details. On one hand, methimazole has caused an elevation in blood glucose. Following methimazole treatment, fasting blood glucose (FBG) and postprandial blood glucose peak values decreased relative to pretreatment [6].
Meanwhile, methimazole has been associated with insulin autoimmune syndrome (IAS), an uncommon cause of hypoglycemia in which the person is diagnosed with insulin-binding autoantibodies. In a case report, a patient with IAS taking methimazole suffered severe hypoglycemia [7].
Furthermore, methimazole might hinder the action of antidiabetic medications. Research suggests that antithyroid medications such as methimazole compromise glucose control in diabetic patients [8].
However, the connection between methimazole and glucose isn’t firmly established, and more research is required to shed light on the process.
Does Methimazole Cause Increase in Glucose?
It turns out that the antithyroid drug methimazole has multiple glucose effects in different situations. Some research also indicates that methimazole can cause hyperglycemia (high blood sugar). In a mice study, for example, the methimazole treatment effectively increased blood sugar levels [9].
However, other experiments have revealed that methimazole lowers blood glucose. The blood glucose was drastically reduced in Zucker diabetic fatty (ZDF) rats who were given methimazole [10]. In another study, methimazole and propranolol enhanced insulin resistance and reduced postprandial blood glucose fluctuations in hyperthyroid patients [6].
Intriguingly, some studies have found that methimazole can cause hypoglycemia or low blood sugar in some people. This is usually because of the occurrence of insulin autoantibodies, and this can produce excessive free insulin and, thus, hypoglycemia [11, 12, 13, 7].
In conclusion, the effect of methimazole on glucose levels can vary and may depend on factors such as the individual's health status and the presence of other conditions. Therefore, it's important for healthcare providers to monitor blood glucose levels in patients taking methimazole and adjust treatment as necessary.