Pharmacologic class: Synthetic thyroid 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 produce serious or even life-threatening toxicity, particularly when given with sympathomimetic amines (such as those used for anorectic effects).


Increases basal metabolic rate, helps regulate cell growth and differentiation, and enhances metabolism of lipids, proteins, and carbohydrates


Tablets: 12.5 mcg levothyroxine sodium and 3.1 mcg liothyronine sodium (Thyrolar-¼); 25 mcg levothyroxine sodium and 6.25 mcg liothyronine sodium (Thyrolar-½); 50 mcg levothyroxine sodium and 12.5 mcg liothyronine sodium (Thyrolar-1); 100 mcg levothyroxine sodium and 25 mcg liothyronine sodium (Thyrolar-2); 150 mcg levothyroxine sodium and 37.5 mcg liothyronine sodium (Thyrolar-3)

Indications and dosages


Adults: All dosages individualized. Initially, one tablet Thyrolar-½ P.O., increased by one tablet Thyrolar-¼ P.O. daily until desired effect occurs. Usual maintenance dosage is one tablet Thyrolar-1 or Thyrolar-2 P.O. daily, adjusted within first 4 weeks based on laboratory results.

Congenital hypothyroidism

Children older than age 12: 18.75/75 mcg P.O. daily

Children ages 6 to 11: 12.5/50 to 18.75/75 mcg P.O. daily

Children ages 1 to 5: 9.35/37.5 to 12.5/50 mcg P.O. daily

Children ages 6 to 12 months: 6.25/25 to 9.35/37.5 mcg P.O. daily

Children up to 6 months: 3.1/12.5 to 6.25/25 mcg (Thyrolar-¼) P.O. daily

Dosage adjustment

• Severe, long-standing hypothyroidism

• Cardiovascular disease

• Psychosis or agitation

• Elderly patients


• Hypersensitivity to drug or its components

• Acute myocardial infarction

• Uncorrected thyrotoxicosis

• Uncorrected adrenal insufficiency and coexisting hypothyroidism


Use cautiously in:

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

• elderly patients

• pregnant or breastfeeding patients.


• Know that all dosages are highly individualized.

• Administer single daily dose in morning with or without food.

Adverse reactions

CNS: insomnia, irritability, nervousness, headache

CV: angina pectoris, hypotension, hypertension, increased cardiac output, tachycardia, arrhythmias, cardiovascular collapse

GI: vomiting, diarrhea, cramps

GU: menstrual irregularities

Metabolic: hyperthyroidism

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


Drug-drug. Aminoglutethimide, amiodarone, anabolic steroids, antithyroid drugs, asparaginase, barbiturates, carbamazepine, chloral hydrate, cholestyramine, clofibrate, colestipol, corticosteroids, danazol, diazepam, estrogens, ethionamide, fluorouracil, heparin (with I.V. use), insulin, lithium, methadone, mitotane, nitroprusside, oxyphenbutazone, P-aminosalicyclic acid, perphenazine, phenylbutazone, phenytoin, propranolol, salicylates (large doses), sulfonylureas, thiazides: altered thyroid function test results

Anticoagulants: increased anticoagulant action

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

Cardiac glycosides: decreased cardiac glycoside blood level

Cholestyramine, colestipol: liotrix inefficacy

Theophyllines: decreased theophylline clearance

Drug-diagnostic tests. Thyroid function tests: decreased values

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

Patient monitoring

• Monitor for evidence of overdose, such as signs and symptoms of hyperthyroidism (weight loss, cardiac symptoms, abdominal cramps).

• Watch closely for signs and symptoms of undertreatment.

• In patients with Addison's disease or diabetes mellitus, assess for signs that these conditions are worsening. In diabetic patients, monitor blood glucose level.

• Check vital signs and ECG routinely.

• Monitor thyroid and liver function tests.

• Assess for signs and symptoms of bleeding tendency, especially if patient's taking anticoagulants.

Patient teaching

• Inform patient or parents that drug should be taken in morning with or without food.

• Explain that patient may require lifelong therapy and will need to undergo regular blood testing.

• Advise diabetic patient (or his parents) to monitor patient's blood glucose level closely.

• 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 of therapy 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.


(lye-oh-trix) ,


(trade name),


(trade name)


Therapeutic: hormones
Pharmacologic: thyroid preparations
Pregnancy Category: A


Thyroid supplementation in hypothyroidism.Treatment or suppression of euthyroid goiters and thyroid cancer.Diagnostic agent for suppression tests to differentiate mild hyperthyroidism from thyroid gland autonomy.


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.
Contain T3 (triiodothyronine) and T4 (thyroxine) activity.

Therapeutic effects

Replacement in deficiency states with restoration of normal hormonal balance.


Absorption: Levothyroxine is variably (50–80%) absorbed from the GI tract. 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: T3 (liothyronine)—1–2 days; T4 (thyroxine)—6–7 days.

Time/action profile

Levothyroxine POunknown1–3 wk1–3 wk
Liothyronine POunknown24–72 hr72 hr


Contraindicated in: Hypersensitivity; Recent MI; Hyperthyroidism.
Use Cautiously in: Cardiovascular disease (initiate therapy with lower doses); Severe renal insufficiency; Uncorrected adrenocortical disorders; Geriatric: Geriatric patients are extremely sensitive to thyroid hormones; initial dosage should be reduced.

Adverse Reactions/Side Effects

Usually only seen when excessive doses cause iatrogenic hyperthyroidism

Central nervous system

  • insomnia
  • irritability
  • headache


  • arrhythmias
  • tachycardia
  • angina pectoris


  • abdominal cramps
  • diarrhea
  • vomiting


  • hyperhidrosis


  • hyperthyroidism
  • menstrual irregularities


  • weight loss
  • heat intolerance


  • accelerated bone maturation in children


Drug-Drug interaction

Bile acid sequestrants ↓ absorption of orally administered thyroid preparations.Alters the effectiveness of warfarin (INR will increase 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).



Contains T4 and T3 in a ratio of 4:1
Oral (Adults) Hypothyroidism—Start with 50 mcg levothyroxine/12.5 mcg liothyronine; increase by 50 mcg levothyroxine/12.5 mcg liothyronine q 2–4 wk until desired effect is obtained; usual maintenance dose is 50–100 mcg levothyroxine/12.5–25 mcg liothyronine daily.Myxedema/hypothyroidism with cardiovascular disease—12.5 mcg levothyroxine/3.1 mcg liothyronine/day; increase by 12.5 mcg levothyroxine/3.1 mcg liothyronine q 2–4 wk until desired effect is obtained.
Oral (Geriatric Patients) 12.5–25 mcg levothyroxine/3.1–6.2 mcg liothyronine/day; increase by 12.5–25 mcg levothyroxine/3.1–6.2 mcg liothyronine q 6–8 wk until desired effect is obtained.


Tablets: 12.5 mcg levothyroxine/3.1 mcg liothyronine, 25 mcg levothyroxine/6.25 mcg liothyronine, 50 mcg levothyroxine/12.5 mcg liothyronine, 100 mcg levothyroxine/25 mcg liothyronine, 150 mcg levothyroxine/37.5 mcg liothyronine

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 such as fever are also used.

Potential Nursing Diagnoses

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


  • 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 products containing 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.

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.


a trademark for a thyroid hormone (liotrix).
Mentioned in ?
References in periodicals archive ?
As in the situation with Armour Thyroid, Thyrolar has suddenly become unavailable.
It is true that the USP has required changes in manufacturing requirements for levothyroxine (T4); however, it is not true that the USP required changes for the manufacture of Thyrolar.
Hauser writes, "Thyrolar is a potentially lethal drug, and no one on Thyrolar should engage in a professional fight.
Two products, Armour thyroid tablets (porcine) and Thyrolar (bovine) are FDA-approved drugs.