Triiodothyronine (T3 Liothyronine)
| Triiodothyronine (T3 Liothyronine) |
| Availability Injection: 10 mcg/ml in 1-ml vials Tablets: 5 mcg, 25 mcg, 50 mcg |
| Indications and dosages ➣ Thyroid hormone replacement in mild hypothyroidism Adults: All dosages individualized. Initially, 25 mcg P.O. daily; may increase in increments of 12.5 to 25 mcg/day q 1 to 2 weeks. Usual maintenance dosage is 25 to 75 mcg P.O. daily. ➣ Myxedema Adults: All dosages individualized. Initially, 5 mcg P.O. daily; increase in increments of 5 to 10 mcg/day q 1 to 2 weeks, up to 25 mcg/day. If response still isn’t adequate, increase by 5 mcg to 25 mcg P.O. daily q 1 to 2 weeks until desired response occurs. Usual maintenance dosage is 50 to 100 mcg/day P.O. ➣ Myxedema coma Adults: Initially, 25 to 50 mcg I.V.; after 4 hours, reassess patient’s need for subsequent doses (up to 65 mcg in 24 hours). In cardiovascular disease, initial dosage is 10 to 20 mcg I.V. ➣ Simple goiter Adults: All dosages individualized. Initially, 5 mcg P.O. daily. Increase by 5 to 10 mcg/day q 1 to 2 weeks, up to 25 mcg/day; then increase by 12.5 to 25 mcg P.O. daily q week until desired effect occurs. Usual maintenance dosage is 75 mcg P.O. daily. Children or elderly adults: Initially, 5 mcg P.O once daily. Increase by 5 mcg q 1 to 2 weeks until desired effect occurs. ➣ T3 suppression test to distinguish hyperthyroidism from thyroid gland autonomy Adults: 75 to 100 mcg P.O. daily for 7 days in conjunction with radioactive iodine |
Pharmacokinetics
- Absorption: 95% absorption
- Peak plasma time: PO: 1-2 hr
- Protein bound: 99.7%, but not firmly
- Hepatic, to deiodinated and conjugated metabolites
- Half-life: 2.5 days
- Excretion: Urine, feces
Administration
- Know that all dosages are highly individualized.
- Administer single oral dose in morning with or without food.
- Injectable form is for I.V. use only. Don’t give I.M.
- Infuse each 10-mcg dose over 1 minute.
- Give repeat I.V. doses more than 4 hours but less than 12 hours apart.
- Be aware that in T3 suppression test, radioactive iodine (131I) is given before and after 7-day liothyronine course.
Contraindications
- Hypersensitivity to drug or its components
- Acute myocardial infarction
- Untreated thyrotoxicosis
- Uncorrected adrenal insufficiency and coexisting hypothyroidism
- Artificial rewarming (I.V. form only)
Precautions:
- Cardiovascular disease, severe renal insufficiency, uncorrected adrenocortical disorders, diabetes mellitus
- Elderly patients
- Pregnant or breastfeeding patients.
Adverse reactions
- CNS: insomnia, irritability, nervousness, headache
- CV: tachycardia, angina pectoris, hypotension, hypertension, increased cardiac output, arrhythmias, cardiovascular collapse
- GI: vomiting, diarrhea, cramps
- GU: menstrual irregularities
- Metabolic: hyperthyroidism, hyperglycemia
- Musculoskeletal: accelerated bone maturation (in children), decreased bone density (with long-term use in women)
- Skin: alopecia (in children), diaphoresis
- Other: weight loss, heat intolerance
Patient monitoring
- Monitor for evidence of overdose, including signs and symptoms of hyperthyroidism (weight loss, cardiac symptoms, and abdominal cramps).
- In patients with Addison’s disease or diabetes mellitus, assess for evidence that these conditions are worsening. In diabetic patients, also monitor blood glucose level.
- Monitor vital signs and ECG routinely.
- Check thyroid and liver function tests.
Patient teaching
- Teach patient to take in morning with or without food.
- Explain that patient may require lifelong therapy and will need to undergo regular blood testing.
- Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
- Inform parents that hair loss may occur in children during first few months but that this effect is usually transient.
- As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and foods mentioned above.
Mechanism of Action
- Replaces endogenous thyroid hormone, which may exert its physiologic effects by controlling DNA transcription and protein synthesis. Like endogenous thyroid hormone, liothyronine:
- Increases energy expenditure
- Accelerates the rate of cellular oxidation, which stimulates body tissue growth, maturation, and metabolism
- Regulates differentiation and proliferation of stem cells
- Aids in myelination of nerves and development of synaptic processes in the nervous system
- Regulates growth
- Decreases blood and hepatic cholesterol concentrations
- Enhances carbohydrate and protein metabolism, increasing gluconeogenesis and protein synthesis.
Nursing Considerations
- Be aware that liothyronine is used most often for rapid onset or rapidly reversible thyroid hormone replacement.
- Administer tablet as a single daily dose before breakfast.
- Give I.V. injections more than 4 hours but less than 12 hours apart.
- Evaluate response to therapy by monitoring pulse rate and blood pressure.
- Expect patient to undergo regular tests of thyroid function during therapy.
- Monitor PT of patient receiving anticoagulants because she may require a dosage adjustment.
- Frequently monitor blood glucose level of diabetic patient. Prescriber may reduce antidiabetic drug dosage as thyroid hormone level enters therapeutic range.
- Be aware that liothyronine is used in T3 suppression test to differentiate hyperthyroidism from euthyroidism (normal thyroid function). For this test, 131I uptake test is performed before and after liothyronine administration. Suppression of 131I uptake by 50% indicates normal thyroid function.
REFERENCES
- Robert Kizior, Keith Hodgson, Saunders Nursing Drug handbook,1st edition 2024, Elsevier Publications. ISBN-9780443116070
- McGraw Hill- Drug Handbook, Seventh Edition, 2013, McGraw Hill Education Publications,9780071799430.
- April Hazard, Cynthia Sanoski, Davi’s Drug Guide for Nurses -Sixteenth Edition 2019, FA Davis Company Publications,9780803669451.
- Jones and Bartlet, Pharmacology for Nurses, Second Edition, 2020, Jones and Bartlet Learning Publications, ISBN 9781284141986.
- Nursebro.com, Search – Nursebro
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