SA JOURNAL OF DIABETES & VASCULAR DISEASE
26
VOLUME 8 NUMBER 1 • MARCH 2011
Patient
information
leaflet
Keep and Copy Series
S Afr J Diabetes Dis 2011;
8
: 26.
YOU AND YOUR THYROID SUPPLEMENT
Dr PM van Zyl
Clinical pharmacologist
Levothyroxine (T4) is the preferred drug for the treatment of
hypothyroidism. Liothyronine (T3) is used in extreme cases requiring
rapid response.
TAKING LEVOTHYROXINE
To avoid overdosing, therapy is started at a relatively low dose and then
increased very gradually (every two to four weeks) until thyroid function
tests confirm that the desired level of activity has been reached. If you
have a cardiac problem, therapy will be started at half the normal dose.
Elderly patients require smaller doses in general.
Take the drug on an empty stomach with water, preferably half an hour
to one hour before breakfast and at least four hours apart from antacids,
iron and calcium supplements. Tablets may be crushed and mixed with 5
to 10 ml of water. Capsules must be swallowed whole.
Store the medication at room temperature (25°C) and protect from light
and moisture.
TAKING OTHER MEDICATION WHILE ON THYROID
REPLACEMENT THERAPY
Many drugs can have significant interactions with thyroid hormones. It is
especially important to be vigilant about possible interactions with chronic
drugs and drugs that easily become toxic. Interactions are prevented by
close monitoring, dose adjustments or avoiding a particular drug.
The list below highlights some important ones:
•
Antidiabetic drugs: monitor diabetes control. May require increased
dose of antidiabetic drug.
•
Digitalis: monitor digitalis levels. May require increased dosage of
digitalis.
•
Oestrogen: monitor thyroid function. May require increased thyroid
hormone dose.
•
Kelp: unpredictable effect on thryoid function. AVOID
•
Warfarin: monitor anticoagulant. May require reduced warfarin dose
(may cause bleeding).
AVOID drugs that increase the pulse rate and consult your doctor about
the safety of over-the-counter (OTC) drugs.
GENERIC SUBSTITUTION
If well controlled on a specific brand: DO NOT SWITCH BRANDS, as there
may be significant differences in the amount of drug reaching the blood-
stream.
POSSIBLE SIDE EFFECTS
Side effects are mostly dose related: at high doses you may experience
palpitations, weight loss, increased appetite, diarrhoea, flushing, sweating
and headache. Report these symptoms to the doctor. Thyroid replacement
can potentially aggravate cardiovascular disease, manifesting as angina
and myocardial infarction. Other serious side effects are: liver failure, os-
teopenia, pseudotumor cerebri and seizures.
WHAT ABOUT PREGNANCY AND BREASTFEEDING?
Levothyroxine is safe during all trimesters of pregnancy, as it does not
cross the placenta. Pregnancy may cause requirements to fluctuate. Small
amounts are excreted in breast milk, yet it is considered compatible with
breastfeeding.
WARNINGS
This drug should not be taken if you have an acute myocardial infarction,
are allergic to any component of the product, if you suffer from non-toxic
diffuse goitre or nodular thyroid disease (with suppressed TSH) or have
thyrotoxicosis or uncorrected adrenal insufficiency.
It should never be used for the treatment of obesity. If the thyroid function
is normal, it will be ineffective at normal doses and high doses can cause
life-threatening side effects.
MONITORING THERAPY
Expect the peak effect after three to four weeks. Therapy is monitored
clinically and with a blood test. Thyroid function tests are done four to six
weeks after dose adjustments to confirm whether dosing is optimal.
