Disclaimer:- This is an extract taken from another Yahoo Thyroid
Cancer Support Group :- http://health.groups.yahoo.com/group/thyca
I hope I am not doing anything wrong in copying this information to
this site, but I feel it is extremely important and should be shared
with anyone taking levothyroxine. I for one learned something new by
reading the 'rules' in this extract.

Without a thyroid gland, we are dependent upon taking daily thyroid
hormone replacement. Unfortunately, the highest vigilance in taking
Levothyroxine daily can turn out to be counterproductive if it isn't
stored and taken properly.

When someone's TSH is mysteriously rising with no apparent reason,
that reason almost always turns out to be one of those included below.

In a nutshell ....

RULE 1:
Be consistent. This is the most important rule. While it is best if
you take T4 on an empty stomach, if you always take it in a
particular way with or without food, other medication or whatever -
then be consistent. Your dose can be adjusted to your pill-taking
habits only if you are consistent in how you take them.

RULE 2:
All other things being equal, it is best to take it first thing in
the morning, on an empty stomach, about an hour before you eat, and
with no other medications. In particular, both iron and calcium
tablets should NOT be taken together with thyroid pills, but at least
5 hours later.

Levothyroxine is highly sensitive to light, moisture and humidity;
do not store your Synthroid (or whatever brand you are using)
near the bathroom sink where there might be a lot of humidity.
If they are stored incorrectly, they lose their potency. Forever.

NOTE: Cytomel (T3) is also a thyroid hormone replacement, and should
be treated with the same precautions as levothyroxine (T4).

From Dr. Ain:

The mean replacement dose of levothyroxine is 2.0 micrograms per
kilogram (2.2 lbs) per day. For example, a 165 lb person would
average 150 micrograms daily to suppress their TSH. Of course, there
is a wide range of variation and there are many factors which are
involved.

1. PROPER STORAGE: Levothyroxine (Synthroid, Levoxyl, Levothroid,
etc) is exquisitely sensitive to heat. If exposed to the sun-heated
interior of a parked automobile, or a shelf above the stove, or left
sitting on the radiator, such pills will forever lose their potency,
even if later cooled down. Women (in particular) often make the
mistake of carrying the pill bottle in their purses, which are often
exposed to wide fluctuations in temperature. NOTE: levothyroxine is
also sensitive to light and humidity - k.)

2. EMPTY STOMACH: Absorption is best on an EMPTY stomach: usually best
in the early AM at least one hour before eating breakfast.

3. DO NOT SKIP A PILL: If a pill is missed, always make it up. For
example, if you forgot to take your pills over a weekend, on Monday
you should take all 3 doses together. Since the half-life of
levothyroxine is one week, such a thing is not only NOT dangerous,
but very necessary to avoid losing TSH suppression.

4. Titration of doses to suppress TSH but not cause tachycardia or
other evidence of thyrotoxicosis can be difficult in some patients,
sometimes requiring dose changes of as little as 10%. For that
reason, even missing one pill per week without making it up would
cause a variation of more than 14% of the weekly dose. For that
reason, NEVER miss your pill, or make it up if you do (as in #3
above).

5. AVOID IRON & SOY PRODUCTS AT THE SAME TIME: Iron-containing
medications and iron-containing vitamins will bind to levothyroxine
and interfere with absorption. So will sucralafate (Carafate),
cholestyramine, large doses of aluminum hydroxide gels (Maalox, etc),
and soy protein supplements. If any of these items must be consumed,
they should be taken 5 hours away from the levothyroxine dose.

6. KNOW YOUR PILLS: Not too infrequently, my patients may be given
the wrong dose by the pharmacist. Check your pills BEFORE you leave
the pharmacy. Do not just look at the label. Examine the pill itself.
Note the characteristic color and numbers on the pill which denote
the correct strength. Check the expiration date & ask for the date
from the stock bottle. Levothyroxine pills degrade at around 5% of
the dose per year by just sitting in the bottle. Never use OLD pills
(over one year old) if you have access to fresh ones.

7. PILL REMINDER: If you are the least bit forgetful, buy a day-of-
the-week pill dispenser and use it religiously.

8. If these precepts are followed PRECISELY, your physician should be
able to lower your daily dose to the lowest dose which suppresses
your TSH (I prefer TSH < 0.10) to avoid stimulation of hibernating
thyroid carcinoma cells. This will also permit the least long-term
side effects (however minor) of TSH suppression.

ON MISSED DOSES:
If a dose of levothyroxine (OF ANY BRAND) is missed, then the dose
must be made up as soon as it is recognized, even if it means taking
2 or more pills at once. This is because the drug has a serum half-
life of one week and taking multiple pills to make up forgotten doses
is far safer than missing the doses entirely. I cannot account for
[contradictory manufacturer instructions], except to say that
errors may be made by anyone, even manufacturers. Missing even one
pill in a week changes the administered weekly dosage by 1/7th; a far
greater amount than the 1/10th dose adjustments we make to accurately
titrate a TSH-suppressive dose.