Anti-Thyroid Drugs

You are taking carbimazole, propylthiouracil or methimazole tablets (anti-thyroid drugs) to treat your overactive thyroid gland. The exact dose you need to take is determined by your consultant/doctor/endocrine specialist nurse and will depend on your symptoms, clinical examination and your blood test results. These tablets work by reducing the amount of thyroid hormone that your thyroid gland produces.

You may at times be asked to take thyroid hormone tablets (thyroxine, levothyroxine or eltroxin) in addition to your anti-thyroid tablets and some patients may also be prescribed beta–blockers (Propranolol) to help reduce symptoms.

The anti-thyroid drugs (carbimazole, propylthiouracil or methimazole) have been used for many years. This group of drugs are generally very safe.

Carbimazole may cause abnormalities in the unborn child and therefore women should not become pregnant whilst taking carbimazole treatment.

Most patients have no side effects. Occasionally patients develop an itchy rash or other minor side effects and very rarely jaundice. If this occurs, contact your GP or the telephone number below.

There is one important serious side effect that can occur with anti-thyroid drugs:
Very rarely anti-thyroid drugs can stop the production of white blood cells from the bone marrow. This is important since white blood cells attack viruses/bacteria and help defend the body from infections. This rare side effect does not depend on the dose of the tablets you are taking, or how long you have taken them therefore the following precautions should be taken whilst ever you are taking this treatment.

If you develop a severe sore throat, mouth ulcers, flu–like illness or other unexplained illness, whilst taking anti-thyroid tablets, you should:

1. Stop your anti-thyroid tablets immediately
2. Contact the Endocrine department – number below
3. See your GP the same day for a blood test (white cell count)
4. Attend the Emergency Department for a blood test if your GP surgery is closed
5. Show this leaflet and/or anti-thyroid warning card to the receptionist/doctor/nurse/blood testing department

If you attend for a blood test at the blood testing department at the hospital, you will need a blood request form which you will need to collect from your endocrine nurse/doctor or your GP will provide this form.

It is important that a health care professional knows you are having this blood test so the results can be reviewed as a matter of urgency and then you will be contacted with the outcome of the results.

• If the white cell count is within the normal range (most likely), then you will be asked to restart your anti-thyroid tablets by your Endocrine Team/GP.
• If the white cell count is low then you will be advised by your Endocrine Team/GP not to take any further tablets until we have established a cause. An alternative treatment may be considered following further blood tests.

If you require more details please contact the Specialist Nurses in Endocrinology:
Tel: 01274 382019 Monday – Friday between 8.00am and 4.00pm except Bank Holidays

For out of hour’s enquiries you must contact a GP/NHS 111 Service/999