Liotrix: Dosage, Mechanism/Onset of Action, Half-Life

Boxed Warning

Weight reduction:

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.

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Tablet, oral:

Thyrolar: ¹/₄ [levothyroxine sodium 12.5 mcg and liothyronine sodium 3.1 mcg]

Thyrolar: ¹/₂ [levothyroxine sodium 25 mcg and liothyronine sodium 6.25 mcg]

Thyrolar: 1 [levothyroxine sodium 50 mcg and liothyronine sodium 12.5 mcg]

Thyrolar: 2 [levothyroxine sodium 100 mcg and liothyronine sodium 25 mcg]

Thyrolar: 3 [levothyroxine sodium 150 mcg and liothyronine sodium 37.5 mcg]

Pharmacology

Mechanism of Action

The primary active compound is T₃ (triiodothyronine), which may be converted from T₄ (thyroxine) and then circulates throughout the body to influence growth and maturation of various tissues. Liotrix is uniform mixture of synthetic T₄ and T₃ in 4:1 ratio; exact mechanism of action is unknown; however, it is believed the thyroid hormone exerts its many metabolic effects through control of DNA transcription and protein synthesis; involved in normal metabolism, growth, and development; promotes gluconeogenesis, increases utilization and mobilization of glycogen stores and stimulates protein synthesis, increases basal metabolic rate

Pharmaco*kinetics/Pharmacodynamics

Absorption

Thyroxine (T₄): 40% to 80%; T₃: 95%

Metabolism

Hepatic to triiodothyronine (active); ~80% T₄ deiodinated in kidney and periphery; glucuronidation/conjugation also occurs; undergoes enterohepatic recirculation

Excretion

Urine (major route of elimination); partially feces

Onset of Action

Liothyronine (T₃): ~3 hours

Time to Peak

Serum: T₄: 2-4 hours; T₃: 2-3 days

Half-Life Elimination

T₄: Euthyroid: 6-7 days; Hyperthyroid: 3-4 days; Hypothyroid: 9-10 days

T₃: 2.5 days

Protein Binding

T₄: >99% bound to plasma proteins including thyroxine-binding globulin, thyroxine-binding prealbumin, and albumin

Use: Labeled Indications

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).

Contraindications

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

Dosage and Administration

Dosing: Adult

Hypothyroidism: Oral:

Dosing: Geriatric

Hypothyroidism: Oral: Initial: Levothyroxine 12.5 to 25 mcg/liothyronine 3.1 to 6.25 mcg once daily; may increase by levothyroxine 12.5 mcg/liothyronine 3.1 mcg every 2 to 3 weeks

Dosing: Pediatric

Note: Doses should be adjusted based on clinical response and laboratory parameters; guidelines do not recommend routine use of levothyroxine/liothyronine combinations over levothyroxine monotherapy in the management of hypothyroidism (AAP 2006; ATA [Jonklaas 2014]).

Congenital hypothyroidism: Note: Infants should have therapy initiated at full doses. Oral: Usual daily dosage range:

Infants ≤6 months: Liothyronine (T₃): 3.1 to 6.25 mcg/levothyroxine (T₄): 12.5 to 25 mcg once daily

Infants >6 to 12 months: Liothyronine (T₃): 6.25 to 9.35 mcg/levothyroxine (T₄): 25 to 37.5 mcg once daily

Children 1 to 5 years: Liothyronine (T₃): 9.35 to 12.5 mcg/levothyroxine (T₄): 37.5 to 50 mcg once daily

Children 6 to 12 years: Liothyronine (T₃): 12.5 to 18.75 mcg/levothyroxine (T₄): 50 to 75 mcg once daily

Adolescents: Typical doses > Liothyronine (T₃): 18.75 mcg; levothyroxine (T₄): 75 mcg once daily

Dietary Considerations

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

Storage

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

Liotrix Images

liotrix levothyroxine sodium (T4) 60 mcg / liothyronine sodium (T3) 15 mcg
liotrix levothyroxine sodium (T4) 120 mcg / liothyronine sodium (T3) 30 mcg
liotrix levothyroxine sodium (T4) 180 mcg / liothyronine sodium (T3) 45 mcg

Drug Interactions

Amezinium: Thyroid Products may enhance the stimulatory effect of Amezinium. Monitor therapy

Amiodarone: May diminish the therapeutic effect of Thyroid Products. Monitor therapy

Apalutamide: May diminish the therapeutic effect of Thyroid Products. Monitor therapy

Bile Acid Sequestrants: May decrease the serum concentration of Thyroid Products. Management: Administer oral thyroid products at least 4 h prior to colesevelam, and at least 1 h before or 4-6 h after cholestyramine. Specific recommendations for colestipol are not available. Monitor for decreased concentrations/effects of the thyroid product. Consider therapy modification

Calcium Polystyrene Sulfonate: May decrease the serum concentration of Thyroid Products. Management: To minimize risk of interaction, separate dosing of oral calcium polystyrene sulfonate and thyroid products (eg, levothyroxine) or administer calcium polystyrene sulfonate rectally. Monitor for signs/symptoms of hypothyroidism with concomitant use (oral). Consider therapy modification

Calcium Salts: May diminish the therapeutic effect of Thyroid Products. Management: Separate the doses of the thyroid product and the oral calcium supplement by at least 4 hours. Consider therapy modification

CarBAMazepine: May decrease the serum concentration of Thyroid Products. Monitor therapy

Ciprofloxacin (Systemic): May decrease the serum concentration of Thyroid Products. Monitor therapy

Estrogen Derivatives: May diminish the therapeutic effect of Thyroid Products. Monitor therapy

Fosphenytoin: May decrease the serum concentration of Thyroid Products. Phenytoin may also displace thyroid hormones from protein binding sites. Monitor therapy

Lanthanum: May decrease the serum concentration of Thyroid Products. Management: Administer oral thyroid products at least two hours before or after lanthanum. Consider therapy modification

Test Interactions

T₄-binding globulin (TBG): factors that alter binding in serum (ATA/AACE [Garber 2012]):

Note: T₄ is ~99.97% protein bound. Factors that alter protein binding will affect serum total T₄ levels; however, measurement of serum free T₄ (the metabolically active moiety) has largely replaced serum total T₄ for thyroid status assessment.

Conditions/states that increase TBG binding: Pregnancy, hepatitis, porphyria, neonatal state

Medications that increase TBG binding: Estrogens, 5-fluorouracil, heroin, methadone, mitotane, perphenazine, selective estrogen receptor modulators (eg, tamoxifen, raloxifene)

Conditions/states that decrease TBG binding: Hepatic failure, nephrosis, severe illness

Medications that decrease TBG binding: Androgens, anabolic steroids, glucocorticoids, L-asparaginase, nicotinic acid

Thyroxine (T₄) and Triiodothyronine (T₃): Serum binding inhibitors (ATA/AACE [Garber 2012]):

Medications that inhibit T₄ and T₃ binding: Carbamazepine, furosemide, free fatty acids, heparin, NSAIDS (variable, transient), phenytoin, salicylates

Thyroid gland hormone: Interference with production and secretion (ATA/AACE [Garber 2012]):

Medications affecting iodine uptake: Amiodarone, iodinated contrast agents, iodine, ethionamide

Medications affecting hormone production: Amiodarone, ethionamide, iodinated contrast agents, iodine, sulfonylureas, sulfonamides, thionamides (carbimazole, methimazole, propylthiouracil)

Medications affecting secretion: Amiodarone, iodinated contrast agents, iodine, lithium

Medications inducing thyroiditis: Alemtuzumab, amiodarone, antiangiogenic agents (lenalidomide, thalidomide), denileukin diftitoxin, interferon alpha, interleukins, lithium, tyrosine kinase inhibitors (sunitinib, sorafenib)

Medications potentially causing the development of Graves’: Alemtuzumab, interferon alpha, antiretroviral therapy

Medications potentially ameliorating thyroiditis (if autoimmune) or Graves’: Glucocorticoids

Hypothalamic-pituitary axis and TSH: Interference with secretion (ATA/AACE [Garber 2012]):

Medications decreasing TSH secretion: Bexarotene, dopamine, dopaminergic agonists (bromocriptine, cabergoline), glucocorticoids, interleukin-6, metformin, opiates, somatostatin analogues (octreotide, lanreotide), thyroid hormone analogues

Medications increasing TSH secretion: Amphetamine, interleukin 2, metoclopramide, ritonavir, St John's wort

Medications potentially causing hypophysitis: Ipilimumab

Adverse Reactions

Frequency not defined.

Cardiovascular: Cardiac arrhythmia, chest pain, increased blood pressure, palpitations, tachycardia

Central nervous system: Anxiety, ataxia, headache, insomnia, nervousness

Dermatologic: Alopecia, diaphoresis, pruritus, urticaria

Endocrine & metabolic: Menstrual disease, weight loss

Gastrointestinal: Abdominal cramps, constipation, diarrhea, increased appetite, nausea, vomiting

Neuromuscular & skeletal: Myalgia, tremor, tremor of hands

Respiratory: Dyspnea

Miscellaneous: Fever

<1%, postmarketing, and/or case reports: Allergic skin reaction

Warnings/Precautions

Disease-related concerns:

Adrenal insufficiency: Use with caution in patients with adrenal insufficiency; symptoms may be exaggerated or aggravated; contraindicated in patients with uncorrected adrenal insufficiency. Treatment with glucocorticoids should precede thyroid replacement therapy in patients with adrenal insufficiency (ATA/AACE [Garber 2012]).
Cardiovascular disease: Use with caution and initiate therapy at a lower dose in patients with angina pectoris or other cardiovascular disease; chronic hypothyroidism predisposes patients to coronary artery disease.
Diabetes: Use with caution in patients with diabetes mellitus and insipidus; symptoms may be exaggerated or aggravated.
Myxedema: Use with caution in patients with myxedema; symptoms may be exaggerated or aggravated; initial dosage reduction is recommended in patients with long-standing myxedema.

Special populations:

Elderly: Use with caution in the elderly as these patients are more likely to have compromised cardiovascular function; lower initial dosage is recommended. Suppressed TSH levels may increase risk of atrial fibrillation and mortality secondary to cardiovascular disease (Gharib 2010; Parle 2001). Increase dose slowly and monitor for signs/symptoms of angina (ATA/AACE [Garber 2012]).

Other warnings/precautions:

Infertility (unapproved use): Use is not justified for the treatment of male or female infertility in euthyroid patients.
Weight reduction (unapproved use):[US Boxed Warning]: In euthyroid patients, thyroid supplements are ineffective and potentially toxic for weight reduction. High doses may produce serious or even life-threatening toxic effects, particularly when used with some anorectic drugs.

Monitoring Parameters

TSH 4 to 6 weeks after treatment initiation or dose changes, 4 to 6 months after adequate replacement dose determined, followed by every 12 months thereafter (or more frequently depending on clinical situation) (Jonklaas 2014); T₄, heart rate, blood pressure, clinical signs of hypo- and hyperthyroidism; TSH is the most reliable guide for evaluating adequacy of thyroid replacement dosage in primary thyroid dysfunction. TSH may be elevated during the first few months of thyroid replacement despite patients being clinically euthyroid. In cases where T₄ remains low and TSH is within normal limits, an evaluation of “free” (unbound) T₄ is needed to evaluate further increase in dosage. Free T₄ (not TSH) should be monitored to guide treatment in patients with central hypothyroidism (ATA/AACE [Garber 2012]).

Pregnancy

Pregnancy Considerations

Endogenous thyroid hormones minimally cross the placenta; the fetal thyroid becomes active around the end of the first trimester. Liotrix has not been found to increase the risk of adverse effects following maternal use during pregnancy.

Uncontrolled maternal hypothyroidism may result in adverse neonatal and maternal outcomes. To prevent adverse events, normal maternal thyroid function should be maintained prior to conception and throughout pregnancy. Levothyroxine is considered the treatment of choice for the control of hypothyroidism during pregnancy.

Patient Education

Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)
Patient may experience hair loss (children). Have patient report immediately to prescriber chest pain, fast heartbeat, abnormal heartbeat, headache, shortness of breath, irritability, anxiety, tremors, trouble sleeping, temperature sensitivity, sweating a lot, leg cramps, muscle weakness, abdominal cramps, lack of appetite, increased hunger, excessive weight gain or loss, swelling of arms or legs, lump on neck, diarrhea, vomiting, or menstrual changes (HCAHPS).
Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.

Source: Wolters Kluwer Health. Last updated November 12, 2019.

Liotrix: Dosage, Mechanism/Onset of Action, Half-Life - Medicine.com (2024)