Thyroid for Dummies (21 page)

Thyroid function tests are always done when someone has a multinodular goitre. Depending on the stress the person feels from this growth in the neck and on how important the doctor thinks it is to leave no stone unturned, many, all, or none of the other tests described in this section are carried out.

Treating a Multinodular Goitre

If the nodules of a multinodular goitre aren’t causing symptoms of hyperthyroidism and don’t contain cancer, and if the person has no symptoms, the multinodular goitre is usually left alone.

Doctors used to think they could shrink a multinodular goitre with thyroid hormone, but this is not the case.

If the person dislikes the appearance of his or her neck, or if they are hyperthyroid, radioactive iodine is used to destroy some of the thyroid tissue (see Chapter 6). This treatment works even for large goitres but sometimes results 14_031727 ch09.qxp 9/6/06 10:45 PM Page 106

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in hypothyroidism. Also, in the course of destroying thyroid tissue, a lot of thyroid hormone is released into the blood stream, inducing temporary hyperthyroidism if it isn’t present already. Older people, especially, need to receive antithyroid drugs before using radioactive iodine (see Chapter 6).

Some people (less than 10 per cent) who are given radioactive iodine to shrink a large multinodular goitre, develop Graves’ disease, which is discussed in Chapter 6. This complication happens because tissue is released into the blood stream, and the body forms antibodies against it.

Surgery is very rarely carried out for a multinodular goitre unless a cancer is found. Radioactive iodine is able to treat most of these thyroid glands, even the large ones that grow in a downward direction (substernal). If surgery is needed for a benign multinodular goitre, enough thyroid tissue is left to keep the patient functionally normal. Thyroid hormone pills are not given unless hypothyroidism develops subsequently. Even if they were given straightaway, they wouldn’t prevent such a gland from growing again.

Patients with multinodular goitres should return to their doctors at least annually to have an examination of the thyroid, or earlier when new growth is seen or pain develops.

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Part III

Managing Your

Thyroid

"They guessed Neville had a thyroid problem

because of his excessive thirst, so they put

him on a high fish diet."

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In this part . . .

These chapters clue you into some special situations

that can affect your thyroid, particularly infections and medications you take for other conditions. We explain the most prevalent thyroid disorder, iodine deficiency disease. If you must have thyroid surgery, we tell you what to expect and how to prepare.

Plus, there is plenty you can do to keep your thyroid happy and making those essential hormones in the right quantities. In this part we discuss some ways you can manage your body so that thyroid function takes place in a healthy environment, and give you the low-down on

alternative therapies.

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Chapter 10

Taking Care with Drugs That

Affect Your Thyroid

In This Chapter

ᮣ Realising the scope of the issue

ᮣ Getting to know the effects of specific drugs

ᮣ Avoiding drug interactions

ᮣ Determining whether you’re taking one of these drugs As thyroid hormones affect every cell in your body, you won’t be surprised to hear that lots of drugs have an effect on your thyroid function as an unwanted side effect. Certain chemicals in your food and in the environment can change thyroid function, too. Whether you have high blood pressure, a headache, or heart failure, at some point you’re bound to run into drugs that affect your thyroid function in some way. You need to know about these side effects so that changes in your thyroid hormone levels or your metabolism that result from one of them, doesn’t lead to wrong conclusions about the state of your thyroid health.

In this chapter, you meet most of the important drugs that interact with your thyroid in one way or another.

Revealing the Drug–Food–Thyroid

Connection

Natasha is a 36-year-old woman who’s healthy and wants to avoid having any more children, as her family is complete. She asks her doctor for the oral contraceptive pill. One day, while browsing in a bookstore, she comes upon
Thyroid For Dummies
, by Alan Rubin and Sarah Brewer (Wiley). (She can’t 16_031727 ch10.qxp 9/6/06 10:46 PM Page 110

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miss it; it’s featured in the ‘Must Read’ section of the bookshop.) She opens it and reads on the Cheat Sheet at the front of the book that thyroid problems can run in families. As several of her relatives have an overactive thyroid gland, she returns to her doctor to ask if getting a thyroid function test would be a good idea.

Her doctor, unfortunately, is away, and the inexperienced locum, who has not read the book, still tests thyroid function with a total thyroxine test (refer to Chapter 4). The result is high. He tells Natasha that she may have hyperthyroidism. Natasha reads further in the book and finds that the oestrogen in her oral contraceptive pill raises the amount of thyroid-binding protein in her system. Meanwhile, the free thyroxine, the form of the thyroid hormone that can enter cells and, therefore, have an effect, remains normal. She informs the (embarrassed) locum, who does a free T4 test and a TSH (thyroid-stimulating hormone) test, both of which are normal. No further treatment is needed.

Leonard is a 72-year-old man who is having trouble with a very irregular heartbeat. His doctor places him on a drug to correct irregular heartbeats called amiodarone. About two months later, Leonard’s heartbeat is regular, but he is beginning to feel cold and sleepy. He has gained a few pounds and notices that his skin is dry. His doctor recognises the symptoms of hypothyroidism (check out Chapter 5), sometimes associated with amiodarone. The doctor orders thyroid function tests to confirm the diagnosis and starts Leonard on thyroid hormone. In a month, he has returned to his normal state of health.

Kathy has seen her doctor for many years because of a multinodular goitre, which has needed no treatment until now. At the age of 68, she develops a rapid heartbeat and sees a cardiologist. She is placed on amiodarone (the same medication that Leonard takes), and her heart problem resolves. However, after six weeks, she notices that her heart is beating rapidly again. Not only that, she is losing weight and having trouble sleeping. She feels warm all the time although she is well past her menopause.

Kathy returns to the cardiologist, who recognises that her symptoms are a side effect of amiodarone and refers her to the local thyroid specialist clinic.

Here, the consultant tells Kathy that she has hyperthyroidism due to the effect of amiodarone on her multinodular goitre. He suggests that she takes a drug to control the thyroid and stop taking the amiodarone if the cardiologist can substitute another drug.

Kathy is able to stop the amiodarone and takes a drug called carbimazole, but her condition does not improve. After two months, the thyroid consultant recommends surgery. After the thyroid surgery is performed, Kathy improves dra-matically. She is now able to take the amiodarone and feels fine.

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Chapter 10: Taking Care with Drugs That Affect Your Thyroid
111

George absolutely loves broccoli and consumes prodigious quantities, even at breakfast. He finds that he is often sleepy and cold. He has trouble thinking and making appropriate decisions. He goes to his doctor, who requests blood tests that show a high thyroid stimulating hormone (TSH). The doctor tells George that he is hypothyroid and puts him on thyroid medication.

One night, George and his wife invite Natasha and her husband to dinner. As Natasha watches George consume huge quantities of broccoli, she remarks that she has read in
Thyroid for Dummies
that broccoli contains a substance that reduces thyroid function. George is very surprised to hear this news, but he sharply reduces his broccoli intake after that night. After talking over the situation with his doctor, he also gradually reduces his thyroid hormone replacement. After he’s been off the broccoli for a month, George’s thyroid tests are normal.

How drugs affect your thyroid hormones

Chapter 3 explains how thyroid hormones are

result occurs because it’s the free thyroid hor-

made and released, how they are carried

mone (hormone not bound to protein) that is

around the body, how they are taken up by cells

active in the body, not the hormone that’s

where they do their work, and how they work

attached to protein.

within these cells. Drugs can affect thyroid

The free hormone arrives at the cell where it

function at any one or more of these levels.

needs to do its work, and gets into the cell by

Thyroid hormone is formed when iodine is added

attaching to a special receptor on the cell mem-

to a compound called thyronine. When four

brane. The receptor is yet another place where

iodine molecules are attached to this compound,

certain drugs can prevent thyroid hormone from

the result is thyroxine (T4). When three mole-

doing its job, for example, if they block the

cules of iodine are attached, the compound receptors so no hormone can enter. The situa-produced is triiodothyronine (T3). T3 is also pro-

tion is almost like diabetes, in which plenty of

duced by removing one iodine molecule from

glucose (sugar) is available in the blood stream

thyroxine. Many drugs and food substances

for energy, but it can’t enter the cell where it

block the production of both T4 and T3.

does its work.

After T3 and T4 are produced, they must travel

Once inside the cell, thyroid hormone attaches

in the body to get to their site of action. They are

to the nucleus, where the genetic material is

carried in the blood stream by thyroid-binding

stored. The hormone then encourages a certain

proteins (refer to Chapter 3). Drugs can affect

action to take place within that cell. Various

thyroid function by increasing or decreasing the

drugs can block the hormone’s attachment to

amount of binding protein in the blood. In this

the nucleus or alter the attachment so that it

case, thyroid test results are affected even

doesn’t produce the desired effect.

though thyroid function remains normal. This

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These cases illustrate the broad spectrum of effects that various drugs and foods can have on thyroid function. Some drugs affect thyroid function tests while the thyroid itself is still normal. Other drugs can create hypothyroidism or hyperthyroidism. As if these effects aren’t confusing enough, the same drug given to two different people may cause opposite effects, depending on their particular clinical situation.

This chapter describes the main drugs that affect thyroid function or thyroid function tests. At the end of this chapter, these drugs are grouped according to their main clinical purpose so that you can check if any drug you’re taking – for example, to treat high blood pressure, diabetes, or fluid retention – could affect you. As drugs are mainly described using their generic (non-trademarked) name in the United Kingdom, these generic names are the ones used here.

If you are not certain whether the drug you are taking is likely to affect your thyroid, you can always ask your pharmacist; your pharmacist is probably more of an expert on the way that drugs work, and their possible side effects, than your doctor.

New medicines are coming on to the market almost every day. Although these products get better and better at curing diseases, their other effects are often not known from the few thousand people who test them before they come to market. The side effects of many drugs don’t become clear until hundreds of thousands of people have taken them. Many, if not all, of these new drugs affect the thyroid in one way or another. The people who must pay particular attention are those who have some underlying thyroid disease to begin with.

For example:

ߜ If you’ve had hyperthyroidism (refer to Chapter 6) and it’s under control with antithyroid drugs, a drug containing a lot of iodine will probably cause a recurrence of your disease.

ߜ If you’ve had a multinodular goitre (refer to Chapter 9), iodine will possibly bring on hyperthyroidism.

ߜ If you’re borderline hypothyroid (refer to Chapter 5), iodine or one of the drugs that block thyroid hormone production will bring on clinical hypothyroidism.