Methimazole (Tapazole) - Signs and Symptoms of Overmedication and Side Effects

Methimazole, the generic of Tapazole, is an antithyroid medication for hyperthyroidism. Hyperthyroidism occurs when your thyroid is producing too much of the thyroid hormones T3 and T4. Methimazole blocks these excess thyroid hormones, relieving one's body of the effects and symptoms of hyperthyroidism. There are many benefits to being on methimazole, but there are also over-medication and side effect signs and symptoms that you should be aware of.

Methimazole (Tapazole) Prescribed for Hyperthyroidism

I was put on methimazole in March of 2010, when I ended up in the emergency room for severe hyperthyroidism. The very first dose of 10mg started to relieve the effects and symptoms being hyperthyroid had on my body. Antithyroid medication only lasts about eight hours though and is normally taken three times a day. Unfortunately, the emergency room doctor had only put me on one dose a day. I could tell when the medication was wearing off because I would start shaking, feel tense, get a headache, and my heart rate and blood pressure would go up. I saw my regular doctor a few days after the emergency room visit and she upped my dose to 20mg three times a day.

The Benefits of Methimazole (Tapazole)

The benefits of being on Methimazole became more consistent after my dose was doubled and I was taking it three times a day. It takes six to eight weeks to reach the full benefits of being on an antithyroid medication, so the benefits increased while my hyperthyroid symptoms decreased as the weeks went on. After being on the higher, more frequent dose of Methimazole for about a month, I started to feel good again. This lasted to about six weeks into the medication and then I started feeling horrible again.

Hypothyroidism from Over-medication of Methimazole (Tapazole)

Probably one of the most common side effects of Methimazole is becoming hypothyroid from over-medication by being on either too high of a dose or on a high dose for too long. I personally was on a high dose for a little too long. I needed the high dose at first to calm down the severe effects and symptoms of being extremely hyperthyroid. My dose probably should have been lowered at about six weeks, but I was in between the last appointment with my regular doctor and the first appointment with my endocrinologist. My regular doctor had not wanted to change my dose because I was doing a lot better and she wanted the endocrinologist to decide what to do next. I had been on methimazole for about eight weeks by the time I was able to see the endocrinologist. By this time I had been feeling absolutely exhausted with no energy or strength for a couple of weeks. I was also gaining weight and retaining water, my face was all puffy, especially around my eyes, my voice was weak, and I had terrible headaches. The endocrinologist said she thought I had gone hypothyroid from how long I was on the high dose of methimazole and ordered blood tests. She was right and I had to be taken off of methimazole for a while.

Other Side Effects of Methimazole (Tapazole)

Some of the hypothyroid as well as other side effects of methimazole are listed on the prescription information you receive when you are given this antithyroid medication. There are a couple of more serious side effects though, that may not be included in this information. These side effects are not common, but can be fatal and are therefore important to know if taking methimazole. The first is that methimazole can lower your white blood cell count. This can cause you to be more susceptible to catching illnesses and to bleed more from an injury or medical procedure. Those on methimazole are cautioned to stay away from anyone who is ill, to not receive any live vaccines, and to let your doctor know you are on methimazole before any surgeries or dental care. The second is that methimazole can cause liver problems, that may result in death, especially if you are on this antithyroid medication long term. Anyone on this medication should contact their doctor immediately if they have any of the following signs of liver problems: jaundice (yellow eyes or skin), itching, loss of appetite, or upper-right abdominal pain (stomach pain). You should be checked for elevated liver enzymes by blood tests while on this medication. Many doctors, including mine, recommend being on methimazole for only twelve to eighteen months with the maximum length of time being two years.

From my experience, being on methimazole has been very beneficial, but the dose needs to be monitored closely. Before being put on methimazole, I was so sick from being hyperthyroid I could barely do anything and finally ended up in the emergency room. After starting this medication, I immediately began to feel better and continued to get better as the weeks passed until I had been on the high dose too long. The hypothyroid side effects from the high dose went away in about a week after stopping methimazole for a while. I definitely believe methimazole works and am willing to take it short term, but I am opting for radioactive iodine treatment as a permanent solution since taking this antithyroid medication long term is not recommended.

Further Reading

Hyperthyroidism: Signs and Symptoms

Hashitoxicosis Signs and Symptoms - Hashimoto's Thyroiditis with a Twist

Thyroid Disease: Could You Have It

Sources:

Drugs.com

EMedTV.com