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HOLLY ATKINSON, MD: Hello and welcome to our webcast. I'm
Dr. Holly Atkinson. Hypothyroidism is a common condition among women in
which the amount of thyroid hormone in the body drops below normal. One
treatment strategy involves replenishing the body with a synthetic hormone
called levothyroxine. But how effective is it and how do the various
formulations of the drugs differ? And just what is levothyroxine
anyway?
PAMELA ALLWEISS, MD: We treat hypothyroidism with a
medication called levothyroxine. The body changes levothyroxine that has
four iodines attached and the body converts it to a hormone with three iodines
and it does this in a very physiologic way. We have many different doses
of levothyroxine and we can titrate the dose very easily.
LOREN WISSNER GREENE, MD: Most people now who are
endocrinologists, who are doctors treating thyroid disease, think that it's
important to start treatment sooner rather than later. Most people will
feel much better and realize how much better they feel once they start taking
thyroid hormone in the proper quantities.
HOLLY ATKINSON, MD: As with just about any drug,
levothyroxine has a number of possible side effects. They're usually mild
but women should nonetheless be aware of the potential consequences.
LOREN WISSNER GREENE, MD: Most of the side effects of
levothyroxine therapy are from incorrect dosing. In other words, if you
give too much or too little of the pill you can have side effects. So for
example, if you take too much levothyroxine, you will have the symptoms of an
overactive thyroid, such as having a very rapid heart rate or even having
congestive heart failure, especially in an elderly person who might already have
heart disease.
PAMELA ALLWEISS, MD: On the other hand, if people aren't
on enough, they can have a slow heart rate. They can have high cholesterol
and the fatigue. So there is a very narrow therapeutic index, therapeutic
window that we have to titrate the drugs so that we have the TSH in the normal
range.
LOREN WISSNER GREENE, MD: Fortunately, nowadays we have
some excellent tests for the TSH level which are very sensitive tests to give us
a very precise TSH reading. This allows us to give very precise dosing of
the levothyroxine that a person is taking. What a doctor will generally do
is to make measurements by taking a blood test of the TSH level to make sure
that the dose is correct.
HOLLY ATKINSON, MD: There are different methods of
synthesizing thyroid hormone and this variety is an area of confusion for many
patients. The most important issue is whether there is any difference in
the effectiveness of the compounds.
PAMELA ALLWEISS, MD: There is a very big difference between
synthetic and natural. We say levothyroxine that would be the synthetic
thyroid that would have four iodine molecules on it. The natural thyroid
can be a combination of both the T4 and the T3 and it basically comes from
animal thyroid glands. So every batch can have a different amount of the
active and the less active amount of thyroid. It is much harder to titrate
-- and what we mean by titrate is to carefully measure, carefully adjust the
dose in response to the person's lab tests, symptoms and blood level of their
thyroid hormone.
With the natural, you don't have as many choices. With
the levothyroxine you have many different doses that you can carefully adjust
based on the lab tests and the patient's symptoms.
HOLLY ATKINSON, MD: One formulation of levothyroxine
called Synthroid has recently come under FDA scrutiny. This development
has yet to effect current recommendations. But many patients are concerned
about the status of this very popular drug.
LOREN WISSNER GREENE, MD: In 1997, the FDA issued some
new regulations. And in their new regulations they required that some
drugs that have been around for many, many years, which we call "grandfathered"
drugs just because they've been around for so many years before the FDA
regulations -- now still have to meet the testing requirements of the
FDA.
So drugs like levothyroxine and drugs like digoxin which is a
heart drug and other drugs -- there are more than 200 drugs in this category,
now have to meet the FDA regulations.
PAMELA ALLWEISS, MD: Now the companies, all of the
companies that make levothyroxine have had to put what we call a new drug
application in to the FDA. Many of the professional organizations of
endocrinologists like the American Association of Clinical Endocrinologists, the
American Thyroid Association are very afraid that when people will see in the
newspaper -- "Oh, is my drug going to be taken off the market," that they may
stop the thyroid medication. And we don't want that to happen.
LOREN WISSNER GREENE, MD: This is not an issue of whether
or not this drug is safe or effective. I mean this drug has been around
for more than 40 years and has been safe and effective. It's a matter of
meeting the correct legal requirements of the FDA.
PAMELA ALLWEISS, MD: So we want to spread the message that
levothyroxine and various brands including Synthroid, Levoxyl, etc. are very
safe drugs. Many endocrinologists and specialty societies have trusted
their patients to these drugs for over 40 years. We do not want people to
panic and just stop the medication. Please check with your physicians
first.
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