Brand Name: Synthroid, Levoxyl, L Thyroxine, Levo T, Levothroid, Levothyroxine T4, Levoxine, Tirosint, and Unithroid
Generic Name: levothyroxine sodium
Drug Class: Thyroid products
What Is Levothyroxine and How Does It Work?
Levothyroxine sodium is a drug approved by the FDA as an oral and injectable prescription thyroid hormone medication that is used to treat underactive thyroid (hypothyroidism) and other conditions. Hypothyroidism is a medical term that refers to any state in which a person's thyroid hormone production is below normal. This medication replaces or provides thyroid hormone support, which is normally produced by the thyroid gland. Low thyroid hormone levels can occur naturally or when the thyroid gland is injured by radiation/medications or removed by surgery. Having enough thyroid hormone is important for maintaining normal mental health and physical activity. In children, having enough thyroid hormone is important for normal mental and physical development. Levothyroxine is also know as L-thyroxine.
Symptoms of Hypothyroidism
The symptoms of hypothyroidism are depend on the health of the thyroid and the efficient production of the thyroid hormone, but can include:
- increased cholesterol levels
- hair loss memory loss
- dry, rough skin, and
Levothyroxine sodium should not be used to treat infertility unless it is caused by low thyroid hormone levels.
Dosages of Levothyroxine Should Be Given As Follows:
Adult and Pediatric Dosage Forms & Strengths
Tablet form of medication
- 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg
- 25 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
Capsule (Tirosint) form of medication
- 13 mcg, 25 mcg, 50 mcg, 75 mcg, 88 mcg
- 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg
Powder for injection form of medication
- 100 mcg/vial
- 200 mcg/vial
- 500 mcg/vial
1.7 mcg/kg or 100-125 mcg PO qDay; not to exceed 300 mcg/day
>50 years (or <50 yr with CV disease)
- Usual initial drug dose: 25-50 mcg/day
- May adjust drug dose by 12.5-25 mcg q6-8Week
>50 yr with CV disease
- Usual initial drug dose: 12.5-25 mcg PO qDay
- May adjust drug dose by 12.5-25 mcg q4-6weeks until patient becomes euthyroid and serum TSH concentration normalized; adjustments q6-8weeks also used
- Dose range: 100-125 mcg PO qDay
Initial drug dose: 12.5-25 mcg PO qDay
Adjust drug dose by 25 mcg/day q2-4Week PRN
Initial: 1 mcg/kg PO qDay may be adequate, OR
300-500 mcg IV once, THEN 50-100 mcg qDay until patient is able to tolerate oral administration; may consider smaller doses in patients with cardiovascular disease
Avoid under-treatment or over-treatment with this drug. This may result in adverse effects.
Lower dose of Tirosint capsules may be required compared with standard T4 tablets for hypothyroidism in patients with impaired gastric acid secretion to reach their target TSH levels; Tirosint has shown improved absorption compared with conventional T4 tablets
Check for bioequivalence if switching brands/generics, OR every week after switching from one levothyroxine sodium preparation to another.
Monitor serum thyroid levels; patient may be asymptomatic
- Initially evaluate patients every 6-8 weeks
- Once normalization of thyroid function and serum TSH (thyroid-stimulating hormone) concentration achieved, evaluate every six to 12 months.
Do not use foods that decrease absorption (soybean products) for administering levothyroxine
Administer oral levothyroxine >4 hr apart from drugs known to interfere with absorption
IV/IM 50% of PO
Patients unable to swallow intact tablets
- Crush appropriate dose and place in 5-10 mL of water
- Administer resultant suspension by spoon or dropper immediately, do NOT store
What Are Side Effects Associated with Using Levothyroxine?
Common side effects associated with using levothyroxine include:
- Chest pain (angina pectoris)
- Joint pain
- Congestive heart failure
- Increased pulse
- Heart attack
- Irregular heartbeat
- Choking sensation
- Mood changes
- Heat intolerance
- Muscle weakness
- Pseudomotor cerebri
- Hair loss
- Weight loss
- Shortness of breath
- Fast heart rate
- Decreased bone mineral density
What Other Drugs Interact with Levothyroxine?
If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.
Severe interactions of levothyroxine inlcude:
- sodium iodide i-131
- sucroferric oxyhydroxide
Serious interactions of levothyroxine inlcude:
- antithrombin alfa
- antithrombin iii
Levothyroxine has known moderate interactions with at least 34 different drugs.
Levothyroxine has mild interactions with at least 34 different drugs.
This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products, treatments and medications you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.
What Are Warnings and Precautions for Levothyroxine?
In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction; larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects.
This medication contains levothyroxine. Do not take Synthroid, Levoxyl, L Thyroxine, Levo T, Levothroid, Levothyroxine T4, Levoxine, Tirosint, or Unithroid if you are allergic to levothyroxine or any ingredients contained in this drug.
Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.
Hypersensitivity to thyroid hormone or other ingredients
Synthetic thyroid hormone should not be used in the treatment of obesity or infertility
No contraindications reported by manufacturer for myxedema coma when treated with injection
Effects of Drug Abuse
There are no known effects of drug abuse of thyroid hormone in synthetic form.
Avoid under-treatment or over-treatment, which may result in adverse effects.
Initiate lower dose in elderly, those with angina pectoris, cardiovascular disease, or in those with severe hypothyroidism.
Do NOT generally use levothyroxine sodium preparations interchangeably, due to narrow therapeutic index.
Check for bioequivalence if switching brands/generics.
Avoid beta-blocker use when patients are being treated for cardiovascular complications caused by Levothyroxine abuse.
Synthroid and Unithroid tablets contain lactose.
Not recommended for TSH suppression in patients with thyroid nodules.
Levoxyl tablets swell in mouth: take with full glass of water to avoid choking.
Avoid use in patients with large thyroid nodules or long-standing goiters, or low-normal TSH levels.
Long-term therapy decreases bone mineral density; use lowest dose in postmenopausal women and women using suppressive doses.
Use caution in patients with adrenal insufficiency; may exacerbate symptoms or aggravate them; treatment with glucocorticoids should precede levothyroxine therapy if adrenal insufficiency present.
Pregnancy and Lactation
Medscape. Lescol XL. Fluvastatin.