Dosing & Uses
Dosage Forms & Strengths
Each 60 mg tablet will replace approximately 60-65 mg (1 grain) of desicated thyroid
Liothyronine sodium (T3) is approximately 4 times as potent as levothyroxine (T4)
tablet, T3/T4
- Thyrolar 1/4 (15mg): 3.1/12.5mcg
- Thyrolar 1/2 (30mg): 6.25/25mcg
- Thyrolar 1 (60mg): 12.5/50mcg
- Thyrolar 2 (120mg): 25/100mcg
- Thyrolar 3 (180mg): 37.5/150mcg
Hypothyroidism
1 tab of Thyrolar 1/2 daily; follow with increments of 1 tab of Thyrolar 1/4 q2-3wk
Lower starting dose of 1 tab recommended in long-standing myxedema, especially if cardiovascular impairment suspected where extreme caution recommended
Maintenance: 1 tab Thyrolar 1 to 1 tab Thyrolar 2 per day; failure to respond to tab Thyrolar 3 may suggest lack of compliance or malabsorption
Adjust dose within the first 4 weeks of therapy after proper clinical laboratory evaluations where serum levels of T4 bound and free TSH are measured
Administer before breakfast
Dosage Forms & Strengths
Each 60 mg tablet will replace approximately 60-65 mg (1 grain) of desicated thyroid
Liothyronine sodium (T3) is approximately 4 times as potent as levothyroxine (T4)
tablet, T3/T4
- Thyrolar 1/4 (15mg): 3.1/12.5mcg
- Thyrolar 1/2 (30mg): 6.25/25mcg
- Thyrolar 1 (60mg): 12.5/50mcg
- Thyrolar 2 (120mg): 25/100mcg
- Thyrolar 3 (180mg): 37.5/150mcg
Congenital Hypothyroidism
0-6 months: 3.1/12.5 to 6.25/25 PO;
6-12 months: 6.25/25 to 9.35/37.5 PO;
1-5 years: 9.35/37.5-12.5/50 mcg PO;
6-12 years: 12.5/50-18.75/75 mcg PO;
>12 years: >18.75/75 mcg PO;
Administration: Before breakfast
Interactions
Interaction Checker
No Results
Contraindicated
Serious - Use Alternative
Significant - Monitor Closely
Minor
Contraindicated (1)
- sodium iodide I-131
liotrix will decrease the level or effect of sodium iodide I-131 by Other (see comment). Contraindicated. Use of thyroid products or iodine before and during treatment with sodium iodide I-131 decreases uptake of sodium iodide I-131 by the thyroid gland
Serious - Use Alternative (0)
Monitor Closely (9)
- didanosine
didanosine will decrease the level or effect of liotrix by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor. Applies to didanosine chewable tablets and powder for oral solution; administer 2 hr before or several hours after didanosine oral solution or chewable tablet administration
- insulin degludec
liotrix decreases effects of insulin degludec by pharmacodynamic antagonism. Use Caution/Monitor. Thyroid hormones regulate carbohydrate metabolism, gluconeogenesis, and glycogen stores mobilization; dose of antidiabetic agents may need adjustment and increased frequency of glucose monitoring may be required.
- insulin degludec/insulin aspart
liotrix decreases effects of insulin degludec/insulin aspart by pharmacodynamic antagonism. Use Caution/Monitor. Thyroid hormones regulate carbohydrate metabolism, gluconeogenesis, and glycogen stores mobilization; dose of antidiabetic agents may need adjustment and increased frequency of glucose monitoring may be required.
- insulin inhaled
liotrix decreases effects of insulin inhaled by pharmacodynamic antagonism. Use Caution/Monitor. Thyroid hormones regulate carbohydrate metabolism, gluconeogenesis, and glycogen stores mobilization; dose of antidiabetic agents may need adjustment and increased frequency of glucose monitoring may be required.
- lanthanum carbonate
lanthanum carbonate decreases levels of liotrix by cation binding in GI tract. Use Caution/Monitor. Administer oral thyroid products at least 2 hr before or after lanthanum. Interaction applies only to oral thyroid products only. .
- levonorgestrel oral/ethinylestradiol/ferrous bisglycinate
levonorgestrel oral/ethinylestradiol/ferrous bisglycinate will decrease the level or effect of liotrix by unknown mechanism. Modify Therapy/Monitor Closely. The estrogen component of combined hormonal contraceptives (CHCs) may raise the serum concentrations of thyroxine-binding globulin. Women on thyroid hormone replacement therapy may need increased doses of thyroid hormone with use of CHCs.
- metformin
liotrix decreases effects of metformin by pharmacodynamic antagonism. Use Caution/Monitor. Patient should be closely observed for loss of blood glucose control; when drugs are withdrawn from a patient receiving metformin, patient should be observed closely for hypoglycemia.
- nateglinide
liotrix decreases effects of nateglinide by pharmacodynamic antagonism. Use Caution/Monitor. Coadministration may reduce nateglinide's hypoglycemic action.
- warfarin
liotrix increases effects of warfarin by unspecified interaction mechanism. Use Caution/Monitor.
Minor (7)
- dexlansoprazole
dexlansoprazole decreases levels of liotrix by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- esomeprazole
esomeprazole decreases levels of liotrix by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- furosemide
furosemide increases toxicity of liotrix by Other (see comment). Minor/Significance Unknown. Comment: High doses (greater than 80 mg) of furosemide may inhibit binding of thyroid hormones to carrier proteins and result in transient increase in free thyroid hormones, followed by overall decrease in total thyroid hormone levels.
- lansoprazole
lansoprazole decreases levels of liotrix by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- omeprazole
omeprazole decreases levels of liotrix by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- pantoprazole
pantoprazole decreases levels of liotrix by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
- rabeprazole
rabeprazole decreases levels of liotrix by increasing gastric pH. Applies only to oral form of both agents. Minor/Significance Unknown. Conflicting evidence regarding this interaction exists.
Adverse Effects
Frequency Not Defined
Arrhythmias
Increased blood pressure
Chest pain
Palpitation
Anxiety
Headache
Urticaria
Changes in menstrual cycle
Insomnia
Hyperhydrosis pruritus
Tachycardia
Nervousness
Tremor
Cramps
Increased appetite
Weight loss
Diarrhea
Warnings
Black Box Warnings
Thyroid hormones, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss
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.
Contraindications
Hypersensitivity to thyroid hormone
Acute MI uncomplicated by hypothyroidism, untreated thyrotoxicosis, untreated adrenal insufficiency
Treatment of obesity
Cautions
Caution in angina, cardiovascular disease, HTN, endocrine disorders, elderly
Use caution in patients with adrenal insufficiency (symptoms may become exagerated or aggravated)
Euthroid withdrawn from U.S. market
Use caution in patients with myxedema (symptoms may become exagerated or aggravated)
No advantage over levothyroxine & may do more harm (T3 overdosage) than good
Not for the treatment of female infertility in euthyroid patients
Pregnancy & Lactation
Pregnancy Category: A
Lactation: Small amount excreted into breast milk, use caution
Pregnancy Categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk. C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done. D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk. X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist. NA: Information not available.Pharmacology
Mechanism of Action
Natural thyroid hormone; increases basal metabolic rate, increases utilization and mobilization of glycogen store, promotes gluconeogenesis
Pharmacokinetics
Half-Life (T4): 6-7 days (euthyroid); 3-4 days (hyperthyroid); 9-10 days (hypothyroid)
Half-life (T3): 2.5 days
Onset: 48 hr
Absorption: 40-80% (T4); 95% (T3)
Max effect: 8-10 days
Peak Plasma Time: 12-48 hr
Bioavailability: 50-95%
Protein Bound: 99% (T4)
Metabolism: Liver, also in kidney & intestinal walls
Metabolites: Triiodothyronine (T3)
Excretion: Urine (major), feces
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