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Levothyroxine
Brand names of levothyroxine
- Alti-Thyroxine
- Armour Thyroid
- Eltroxin
- Euthroid [CD]
- Euthyrox
- Levo-T
- Levotabs
- Levothroid
- Levoxine
- Levoxyl
- L-Thyroxine
- Proloid
- Synthroid
- Synthrox
- Syroxine
- Thyroid USP
- Thyrolar [CD]
Usage
To treat patients with an
underactive thyroid gland,
goiter (enlarged thyroid
gland), and benign and malignant (noncancerous and cancerous)
thyroid nodules.
How it works
Levothyroxine acts in the
body as a substitute for natural thyroid hormone.
Side effects
- Serious:
- Less common:
Possible interactions
- Other medicaments:
Levothyroxine may increase the effects of:
- warfarin (Coumadin) and increase the risk of
bleeding; decreased
anticoagulant dose is usually needed. More frequent INR testing (prothrombin
time or protime) are needed.
Levothyroxine may decrease the effects of:
- digoxin (Lanoxin), when correcting hypothyroidism; a larger dose of digoxin
may be needed.
Levothyroxine taken concurrently with:
- antacids may cause decreased levothyroxine absorption and a decreased
therapeutic effect.
- all antidiabetic medicaments (insulin and oral hypoglycemic agents) may require an
increased dose to obtain proper control of
blood sugar levels.
- benzodiazepines (Librium and others) can enhance the toxic or
therapeutic effects of both medicaments.
- conjugated estrogens (Premarin) may require an increased levothyroxine
dose.
- tricyclic antidepressants may cause an increase in
activity of both medicaments.
The following medicaments may decrease the effects of levothyroxine:
- cholestyramine (Cuemid, Questran)-may reduce its absorption; intake of
the two medicaments should be separated by 5 hours.
- colestipol (Colestid).
- iron salts-by decreasing absorption.
- lovastatin (Mevacor).
- phenytoin (Dilantin) or fosphenytoin (Cerebyx)-can increase levothyroxine
removal (clearance).
- ritonavir (Norvir).
- sodium polystyrene sulfonate (Kayexalate).
- sucralfate (Carafate).
- Foods:
- Enteral formulas for nutrition support that contain soybeans may
increase the fecal elimination of thyroxine.
- Herbal medicines or minerals:
- Horseradish root might worsen low thyroid (hypothyroidism) or blunt effectiveness of therapy.
Calcium doses (if taken)
should be separated from levothyroxine doses by four hours.
Cabbage and
iodine may worsen goiters and exacerbate hypothyroidism.
Gamma
oryzanol (extracted from rice bran oil) can lower thyroid stimulating
hormone (TSH) and change test results. Tiratricol is a naturally occurring
metabolite of thyroxine and triiodothyronine. In theory, tiratricol may
enhance the adverse action and effects of bungleweed,
wild thyme and balm leaf.
Talk to your doctor before adding any herbal medicines to levothyroxine.
- Exposure to heat:
- This medicament may decrease individual tolerance to warm
environments, increasing discomfort due to heat. Consult your physician if you
develop symptoms of overdose during the warm months of the year.
- Heavy exercise or exertion:
- Use caution if you have angina (coronary artery
disease). This medicament may increase the frequency or severity of angina during
physical activity.
- Discontinuation:
- Must be taken continually on a regular schedule to correct
thyroid deficiency. Never stop it without talking to your doctor.
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