liothyronine

Synthetic form of triiodothyronine (T₃). Replacement of or supplementation to endogenous thyroid hormones.
Principal effect is increasing metabolic rate of body tissues:
- Promote gluconeogenesis,
- Increase utilization and mobilization of glycogen stores,
- Stimulate protein synthesis,
- Promote cell growth and differentiation,
- Aid in the development of the brain and CNS.

Therapeutic effects:

Replacement in hypothyroidism to restore normal hormonal balance.

Pharmacokinetics ⬆ ⬇

Absorption: Well absorbed.

Distribution: Distributed into most body tissues. Thyroid hormones do not readily cross the placenta; minimal amounts enter breast milk.

Metabolism/Excretion: Metabolized by the liver and other tissues. Thyroid hormone undergoes enterohepatic recirculation and is excreted in the feces via the bile.

Half-Life: 1–2 days.

Time/Action Profile ⬆ ⬇

ROUTE	ONSET	PEAK	DURATION
PO	unknown	24–72 hr	72 hr
IV	unknown	unknown	unknown

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hypersensitivity;
Uncorrected adrenal insufficiency;
Hyperthyroidism.

Use Cautiously in:

Cardiovascular disease (initiate therapy with lower doses);
Severe renal impairment;
Diabetes mellitus;
OB: Levothyroxine is preferred in pregnancy;
Lactation: Use during breastfeeding only if potential maternal benefit justifies potential risk to infant;
Geri: Older adults have sensitivity to thyroid hormones; initial dose should be .

Adv. Reactions/Side Effects ⬆ ⬇

Usually only seen when excessive doses cause iatrogenic hyperthyroidism

CV: angina, arrhythmias, tachycardia

Derm: hyperhidrosis

Endo: heat intolerance, hyperthyroidism, menstrual irregularities

GI: abdominal cramps, diarrhea, vomiting

Metab: weight loss

MS: accelerated bone maturation (children)

Neuro: headache, insomnia, irritability

Interactions ⬆ ⬇

Drug-drug:

Bile acid sequestrants↓ absorption of orally administered thyroid preparations.
Alters the effectiveness of warfarin (INR will ↑ with thyroid hormone supplementation).
May ↑ requirement for insulin or oral hypoglycemic agents in diabetics.
Concurrent estrogen therapy may ↑ thyroid replacement requirements.
↑cardiovascular effects with adrenergics (sympathomimetics).

Route/Dosage ⬆ ⬇

Hypothyroidism

PO (Adults ): 25 mcg once daily; may ↑ by 12.5–25 mcg/day every 1–2 wk; usual maintenance dose is 25–75 mcg once daily.
PO Geriatric Patients or Patients with Cardiovascular Disease): 5 mcg /day initially; ↑ by no more than 5 mcg/day every 1–2 wk.
PO (Children ): 5 mcg once daily; ↑ by 5 mcg/day every 3–4 days until desired response; usual maintenance dose is 20 mcg once daily (infants); 50 mcg once daily (1 yr old); and 75 mcg once daily (>3 yr old).

Well-Differentiated Thyroid Cancer

PO (Adults ): Dose used should target TSH levels within the desired therapeutic range (may require higher doses).

Thyroid Suppression Test

PO (Adults ): 75–100 mcg once daily for 7 days. Radioactive iodine uptake should be determined before and after the 7–day treatment course.

Myxedema Coma

IV (Adults ): 25–50 mcg initially (if cardiovascular disease is present, initial dose should be 10–20 mcg). Additional doses may be given, to a total of at least 65 mcg/day (not to exceed 100 mcg/day). Doses should be ≥4 hr but not more than 12 hr apart.

Availability ⬆ ⬇

(Generic available)

Tablets: 5 mcg; 25 mcg; 50 mcg
Solution for injection: 10 mcg/mL

Assessment ⬆ ⬇

Assess apical pulse and BP prior to and periodically during therapy. Assess for tachyarrhythmias and chest pain.
Children: Monitor height, weight, and psychomotor development.

Lab Test Considerations:

Monitor thyroid function studies prior to and every 6 mo during therapy.
- Monitor blood and urine glucose in diabetic patients. Insulin or oral hypoglycemic dose may need to be increased.

Toxicity and Overdose:

Overdose is manifested as hyperthyroidism (tachycardia, chest pain, nervousness, insomnia, diaphoresis, tremors, weight loss). Usual treatment is to withhold dose for 2–6 days. Acute overdose is treated by induction of emesis or gastric lavage, followed by activated charcoal. Sympathetic overstimulation may be controlled by antiadrenergic drugs (beta blockers), such as propranolol. Oxygen and supportive measures to control symptoms are also used.

Implementation ⬆ ⬇

Do not confuse liothyronine with levothyroxine.
PO: Administer as a single dose, preferably before breakfast to prevent insomnia.
- Initial dose is low, especially in geriatric and cardiac patients. Dose is increased gradually, based on thyroid function tests. Side effects occur more rapidly with liothyronine because of its rapid onset of effect.
- For patients with difficulty swallowing, tablets can be crushed and placed in 5–10 mL of water and administered immediately via dropper or spoon; do not store suspension.

IV Administration:

IV: Liothyronine injection is for IV use only. Do not give IM or SUBQ. Administer doses at least 4 hr and not more than 12 hr apart. Base doses on continuous monitoring of patient and response to therapy.
- Resume PO therapy as soon as patient is stable and able to take PO medication. When switching to PO therapy, discontinue IV liothyronine and initiate PO at low dose, increasing gradually according to patient’s response.
May be administered undiluted.
Rate: Administer as a bolus.

Patient/Family Teaching ⬆ ⬇

Instruct patient to take medication as directed at the same time each day. Take missed doses as soon as remembered unless almost time for next dose. If more than 2–3 doses are missed, notify health care professional. Do not discontinue without consulting health care professional.
- Explain to patient that medication does not cure hypothyroidism; it provides a thyroid hormone supplement. Therapy is lifelong.
- Advise patient to notify health care professional if headache, nervousness, diarrhea, excessive sweating, heat intolerance, chest pain, increased pulse rate, palpitations, weight loss >2 lb/wk, or any unusual symptoms occur.
- Caution patient to avoid taking other medications concurrently with thyroid preparations unless instructed by health care professional.
- Instruct patient to inform health care professionals of thyroid therapy.
- Emphasize importance of follow-up exams to monitor effectiveness of therapy. Thyroid function tests are performed at least yearly.
Pedi: Discuss with parents the need for routine follow-up studies to ensure correct development. Inform patient that partial hair loss may be experienced by children on thyroid therapy. This is usually temporary.
Rep: Advise females of reproductive potential to notify health care professional if pregnancy is planned or suspected or if breastfeeding. In women with pre-existing hypothyroidism: thyroid hormone dose requirements may increase during pregnancy. Monitor serum TSH and free-T4 as soon as pregnancy is confirmed and during each trimester of pregnancy. In patients with primary hypothyroidism: maintain serum TSH in the trimester-specific reference range. For patients with serum TSH above the normal trimester-specific range, increase the dose of thyroid hormone and measure TSH every 4 wks until a stable dose is reached and serum TSH is within the normal trimester-specific range. Reduce thyroid hormone dose to pre-pregnancy levels immediately after delivery and measure serum TSH levels 4 to 8 wks postpartum to ensure correct dose.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇

Action ⬆ ⬇