Liotrix

Since thyroid hormone occurs naturally in the body, almost anyone can take liotrix. However, you may not be able to use this medication if you have a thyroid disorder called thyrotoxicosis, or an adrenal gland problem that is not controlled by treatment.

To make sure you can safely take liotrix, tell your doctor if you have any of these other conditions:

• heart disease, angina (chest pain);
• coronary artery disease;
• congestive heart failure;
• any type of diabetes; or
• problems with your pituitary or adrenal gland.

FDA pregnancy category A. Liotrix is not expected to harm an unborn baby. However, tell your doctor if you become pregnant, since your dose needs may be different during pregnancy.

Small amounts of liotrix can pass into breast milk, but this is not expected to harm a nursing baby. However, do not use this medication without telling your doctor if you are breast-feeding a baby.

Absorption

Bioavailability

Levothyroxine (T4): Variably absorbed from the GI tract (range: 40–80%).b j Extent of absorption is increased in the fasting state and decreased in malabsorption states.b j

Liothyronine (T3): Almost completely absorbed from the GI tract (about 95%).b h j

Onset

Liothyronine has a more rapid onset of action than levothyroxine (24–72 hours versus 1–3 weeks).h i j

Distribution

Extent

T4 is distributed throughout most body tissues and fluids; highest concentrations found in liver and kidneys.j

Thyroid hormones do not readily cross the placenta;b j q however, some transfer does occur, as evidenced by levels in cord blood of athyrotic fetuses being approximately one-third maternal levels.q

Thyroid hormones are minimally distributed into breast milk.b j q

Plasma Protein Binding

Circulating thyroid hormones are >99% bound to serum proteins, including TBG, thyroxine-binding prealbumin (TBPA), and albumin.b j q T4 is more extensively and firmly bound to TBG and TBPA than T3.b j q Only unbound hormone is metabolically active.b q

Elimination

Metabolism

T4 and T3 are metabolized principally in the liver through sequential deiodination.b j q Approximately 80% of the daily dose of T4 is deiodinated to yield equal amounts of T3 and reverse T3 (rT3).j q T3 and rT3 are further deiodinated to diiodothyronine.j q Thyroid hormones are also metabolized via conjugation with glucuronides and sulfates and excreted directly into the bile and gut where they undergo enterohepatic recirculation.b j q

Elimination Route

Thyroid hormones are primarily eliminated by the kidneys.q A portion of the conjugated hormone reaches the colon unchanged and is eliminated in the feces.q Approximately 20% of T4 is eliminated in stool.q Urinary excretion of T4 decreases with age.q

Half-life

T4: Approximately 6–7 days.h i j

T3: Approximately 1–2 days.c h i j

These plasma half-lives are decreased in patients with hyperthyroidism and increased in those with hypothyroidism.h i j

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

U.S. Pharmacopeia, an official public standards-setting authority for all prescription and over-the-counter medicines and other health care products manufactured or sold in the United States, has mandated new specifications for a component used in the manufacturing of Thyrolar. As a result, all strengths of Thyrolar are currently on long-term back order while Forest makes the modifications necessary to meet these new specifications. Forest is working diligently to complete these modifications. In the meantime, patients should speak with their physician regarding appropriate treatment for their condition, and check for future updates on the availability of Thyrolar through the Forest product availability toll-free hotline at (866) 927-3260.

• Tell all of your health care providers that you take this medicine. This includes your doctors, nurses, pharmacists, and dentists.
• Do not run out of liotrix.
• If you have high blood sugar (diabetes), you will need to watch your blood sugar closely.
• Have blood work checked as you have been told by the doctor. Talk with the doctor.
• If you are taking warfarin, talk with your doctor. You may need to have your blood work checked more closely while you are taking it with this medicine.
• If you are 65 or older, use liotrix with care. You could have more side effects.
• Use with care in children. Talk with the doctor.
• Tell your doctor if you are pregnant or plan on getting pregnant. You will need to talk about the benefits and risks of using this medicine while you are pregnant.
• Tell your doctor if you are breast-feeding. You will need to talk about any risks to your baby.

If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

• Levothyroxine and Liothyronine
• Liothyronine and Levothyroxine
• T3/T4 Liotrix

Hypothyroidism: Replacement or supplemental therapy in hypothyroidism

Note: Clinical practice guidelines currently do not recommend routine use of levothyroxine/liothyronine combinations over levothyroxine monotherapy in the management of hypothyroidism (Jonklaas 2014).

Hypersensitivity to liotrix or any component of the formulation; uncorrected adrenal insufficiency; untreated thyrotoxicosis

Hypothyroidism: Oral:

Initial: Levothyroxine 25 mcg/liothyronine 6.25 mcg once daily; a lower initial dose (levothyroxine 12.5 mcg/liothyronine 3.1 mcg) is recommended in patients with long-standing myxedema, especially if cardiovascular impairment coexists (if angina occurs, reduce dose). Dose may be increased in increments of levothyroxine 12.5 mcg/liothyronine 3.1 mcg every 2 to 3 weeks.

Usual maintenance dose: Levothyroxine 50 to 100 mcg/liothyronine 12.5 to 25 mcg once daily; inadequate response despite adequate dosage replacement may indicate nonadherence, poor absorption, excessive elimination, or inactivity of the preparation.

Take once a day on an empty stomach 30-60 minutes before meals.

Store at 2°C to 8°C (36°F to 46°F). Protect from light.

Drugs with thyroid hormone activity, alone or with other therapeutic agents have been used for the treatment of obesity. 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.