Cytomel


Cytomel

 [si´to-mel] trademark for a preparation of liothyronine sodium, a thyroid hormone preparation.

liothyronine sodium (T3)

Cytomel, Tertroxin (UK), Triostat

Pharmacologic class: Synthetic thyroxine hormone

Therapeutic class: Thyroid hormone replacement

Pregnancy risk category A

FDA Box Warning

• Drug has been used (alone or with other agents) to treat obesity. In euthyroid patients, doses within range of daily hormonal requirements are ineffective for weight loss. Larger doses may cause serious or life-threatening toxicity, particularly when given with sympathomimetic amines (such as those used for anorectic effects).

Action

Synthetic form of triiodothyronine (T3). Regulates cell growth and differentiation; increases metabolism of lipids, proteins, and carbohydrates; and enhances aerobic mitochondrial function. Also reduces tissue lactic acidosis.

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

Dosage adjustment

• Severe, long-standing hypothyroidism

• Cardiovascular disease

• Psychosis or agitation

• Elderly patients

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

Use cautiously in:

• cardiovascular disease, severe renal insufficiency, uncorrected adrenocortical disorders, diabetes mellitus

• elderly patients

• pregnant or breastfeeding patients.

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.

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

Interactions

Drug-drug. Anabolic steroids, antithyroid drugs, asparaginase, barbiturates, carbamazepine, chloral hydrate, clofibrate, corticosteroids, danazol, estrogens, fluorouracil, heparin (with I.V. use), lithium, methadone, mitotane, oxyphenbutazone, perphenazine, phenylbutazone, phenytoin, propranolol, salicylates (large doses), sulfonylureas: altered thyroid function test results

Anticoagulants: increased anticoagulant action

Beta-adrenergic blockers (selected): impaired beta blocker action

Cardiac glycosides: decreased cardiac glycoside blood level

Cholestyramine, colestipol: liothyronine inefficacy

Theophyllines: decreased theophylline clearance

Drug-diagnostic tests. Thyroid function tests: altered values

Drug-food. Foods high in iron or fiber, soybeans: decreased drug absorption

Patient monitoring

See 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.

liothyronine

(lye-oh-thye-roe-neen) liothyronine,

Cytomel

(trade name),

l-triiodothyronine

(trade name),

T3

(trade name),

Triostat

(trade name)

Classification

Therapeutic: hormones
Pharmacologic: thyroid preparations
Pregnancy Category: A

Indications

Thyroid supplementation in hypothyroidism.Treatment or suppression of euthyroid goiters.Diagnostic agent for suppression tests to differentiate mild hyperthyroidism from thyroid gland autonomy.Treatment of myxedema coma (IV formulation).

Action

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: Liothyronine is well absorbed.Distribution: Distributed into most body tissues. Thyroid hormones do not readily cross the placenta; minimal amounts enter breast milk.Metabolism and 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

ROUTEONSETPEAKDURATION
Liothyronine POunknown24–72 hr72 hr
Liothyronine IVunknownunknownunknown

Contraindications/Precautions

Contraindicated in: Hypersensitivity; Recent MI; Hyperthyroidism.Use Cautiously in: Cardiovascular disease (initiate therapy with lower doses); Severe renal insufficiency; Uncorrected adrenocortical disorders; Geriatric: ↑sensitivity to thyroid hormones; initial dose should be ↓.

Adverse Reactions/Side Effects

Usually only seen when excessive doses cause iatrogenic hyperthyroidism

Central nervous system

  • insomnia
  • irritability
  • headache

Cardiovascular

  • arrhythmias
  • tachycardia
  • angina pectoris

Gastrointestinal

  • abdominal cramps
  • diarrhea
  • vomiting

Dermatologic

  • hyperhidrosis

Endocrinologic

  • hyperthyroidism
  • menstrual irregularities

Metabolic

  • weight loss
  • heat intolerance

Musculoskeletal

  • accelerated bone maturation in children

Interactions

Drug-Drug interaction

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

Oral (Adults) Mild hypothyroidism—25 mcg once daily; may ↑ by 12.5–25 mcg/day q 1–2 wk intervals; usual maintenance dose is 25–50 mcg/day. Myxedema—2.5–5 mcg once daily initially; ↑ by 5–10 mcg/day q 1–2 wk up to 25 mcg/day, then ↑ by 12.5–25 mcg/day; usual maintenance dose is 25–50 mcg/day. Simple goiter—5 mcg once daily initially; ↑ by 5–10 mcg/day q 1–2 wk up to 25 mcg/day, then ↑ by 12.5–25 mcg/day q wk until desired effect is obtained; usual maintenance dose is 50–100 mcg/day. T3 suppression test—75–100 mcg daily for 7 days. Radioactive 131I is administered before and after 7-day course.Oral (Geriatric Patients or Patients with Cardiovascular Disease) 5 mcg /day initially; ↑ by no more than 5 mcg/day q 2 wk.Intravenous (Adults) Myxedema coma—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 at least 4 hr but not more than 12 hr apart.

Availability (generic available)

Tablets: 5 mcg, 25 mcg, 50 mcg Injection: 10 mcg/mL

Nursing implications

Nursing 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 during therapy.
    • Monitor blood and urine glucose in diabetic patients. Insulin or oral hypoglycemic dose may need to be increased.
    • 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.

Potential Nursing Diagnoses

Deficient knowledge, related to medication regimen (Patient/Family Teaching)

Implementation

  • Oral: 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.
  • Intravenous Administration
  • pH: No Data.
  • Intravenous: Liothyronine injection is for IV use only. Do not give IM or subcut. 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.
  • Pediatric: 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.

Evaluation/Desired Outcomes

  • Resolution of symptoms of hypothyroidism and normalization of hormone levels.