Medical Editor: John P. Cunha, DO, FACOEP
What Is Cytomel?
Cytomel (liothyronine sodium) is a synthetic thyroid hormone used to treat hypothyroidism (low thyroid hormone). Cytomel is also used to treat or prevent goiter (enlarged thyroid gland), and is also given as part of a medical tests for thyroid disorders. Cytomel is available in generic form.
What Are Side Effects of Cytomel?
Cytomel may cause serious side effects including:
- headache,
- irritability,
- trouble sleeping,
- nervousness,
- increased sweating,
- heat intolerance,
- diarrhea, and
- menstrual changes
Get medical help right away, if you have any of the symptoms listed above.
Common side effects of Cytomel include:
- nausea.
In rare cases, temporary hair loss may occur during the first few months of starting Cytomel (especially in children). Tell your doctor immediately if you experience unlikely but serious signs of too much thyroid hormone including:
- headache,
- irritability,
- trouble sleeping,
- nervousness,
- increased sweating,
- heat intolerance,
- diarrhea, and
- menstrual changes.
Seek medical care or call 911 at once if you have the following serious side effects:
- Serious eye symptoms such as sudden vision loss, blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights;
- Serious heart symptoms such as fast, irregular, or pounding heartbeats; fluttering in your chest; shortness of breath; and sudden dizziness, lightheadedness, or passing out;
- Severe headache, confusion, slurred speech, arm or leg weakness, trouble walking, loss of coordination, feeling unsteady, very stiff muscles, high fever, profuse sweating, or tremors.
This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.
Dosage for Cytomel
To treat mild hypothyroidism the recommended starting dose of Cytomel is 25 mcg daily. Usual maintenance dose is 25 to 75 mcg daily. Dosage for other conditions varies.
What Drugs, Substances, or Supplements Interact with Cytomel?
Cytomel may interact with birth control pills or hormone replacement therapy, blood thinners, digoxin, insulin or oral diabetes medication, medications that contain iodine, antidepressants, aspirin or other salicylates, or steroids. Tell your doctor all medications you use.
Cytomel During Pregnancy and Breastfeeding
Current information shows Cytomel may be used during pregnancy. Consult your doctor before becoming pregnant. This medication passes into breast milk. While there have been no reports of harm to nursing infants, consult your doctor before breastfeeding.
Additional Information
Our Cytomel (liothyronine sodium) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
QUESTION
Where is the thyroid gland located? See AnswerGet emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Stop using liothyronine and call your doctor if you have symptoms of thyroid toxicity, such as chest pain, fast or pounding heartbeats, feeling hot or nervous, or sweating more than usual.
Also call your doctor at once if you have:
- weak or shallow breathing;
- confusion;
- a feeling of being cold all the time;
- changes in weight or appetite;
- chest pressure spreading to your jaw or shoulder;
- a light-headed feeling, like you might pass out;
- severe headaches, ringing in your ears, dizziness, vision problems, pain behind your eyes;
- a seizure; or
- (in a child or teenager) pain, stiffness, and trouble moving the legs.
Common side effects may include:
- trouble breathing;
- headache;
- tremors, feeling nervous or irritable;
- muscle weakness;
- increased appetite;
- diarrhea;
- irregular menstrual periods;
- weight loss;
- feeling hot;
- rash; or
- sleep problems (insomnia).
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
SLIDESHOW
Hyperthyroidism Symptoms and Treatment See SlideshowSIDE EFFECTS
Adverse reactions associated with CYTOMEL therapy are primarily those of hyperthyroidism due to therapeutic overdosage [see WARNINGS AND PRECAUTIONS and OVERDOSE]. They include the following:
General: fatigue, increased appetite, weight loss, heat intolerance, fever, excessive sweating
Central nervous system: headache, hyperactivity, nervousness, anxiety, irritability, emotional lability, insomnia
Musculoskeletal: tremors, muscle weakness and cramps
Cardiovascular: palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest
Respiratory: dyspnea
Gastrointestinal: diarrhea, vomiting, abdominal cramps, elevations in liver function tests
Dermatologic: hair loss, flushing
Endocrine: decreased bone mineral density
Reproductive: menstrual irregularities, impaired fertility
Adverse Reactions In Pediatric Patients
Pseudotumor cerebri and slipped capital femoral epiphysis have been reported in pediatric patients receiving thyroid replacement therapy. Overtreatment may result in craniosynostosis in infants and premature closure of the epiphyses in pediatric patients with resultant compromised adult height.
Hypersensitivity Reactions
Hypersensitivity reactions to inactive ingredients have occurred in patients treated with thyroid hormone products. These include urticaria, pruritus, skin rash, flushing, angioedema, various gastrointestinal symptoms (abdominal pain, nausea, vomiting and diarrhea), fever, arthralgia, serum sickness and wheezing.
DRUG INTERACTIONS
Drugs Known To Affect Thyroid Hormone Pharmacokinetics
Many drugs can exert effects on thyroid hormone pharmacokinetics (e.g. absorption, synthesis, secretion, catabolism, protein binding, and target tissue response) and may alter the therapeutic response to CYTOMEL (see Tables 1 – 4).
Table 1: Drugs That May Decrease T3 Absorption (Hypothyroidism)
| Potential impact: Concurrent use may reduce the efficacy of CYTOMEL by binding and delaying or preventing absorption, potentially resulting in hypothyroidism.Effect | |
| Drug or Drug Class | Effect |
Bile Acid Sequestrants
|
Bile acid sequestrants and ion exchange resins are known to decrease thyroid hormones absorption. Administer CYTOMEL at least 4 hours prior to these drugs or monitor TSH levels. |
Table 2: Drugs That May Alter Triiodothyronine (T3) Serum Trans port Without Affecting Free Thyroxine (FT4) Concentration (Euthyroidism)
| Drug or Drug Class | Effect |
| Clofibrate Estrogen containing oral contraceptives Estrogens (oral) Heroin / Methadone 5-Fluorouracil Mitotane Tamoxifen |
These drugs may increase serum thyroxine-binding globulin (TBG) concentration. |
| Androgens / Anabolic Steroids Asparaginase Glucocorticoids Slow-Release Nicotinic Acid |
These drugs may decrease serum TBG concentration. |
| Salicylates (>2 g/day) | Salicylates inhibit binding of T4 and T3 to TBG and transthyretin. An initial increase in serum FT4 is followed by return of FT4 to normal levels with sustained therapeutic serum salicylate concentrations, although total T4 levels may decrease by as much as 30%. |
| Other drugs: Carbamazepine Furosemide (>80 mg IV) Heparin Hydantoins Non- Steroidal Antiinflammatory Drugs - Fenamates |
These drugs may cause protein binding site displacement. Furosemide has been shown to inhibit the protein binding of T4 to TBG and albumin, causing an increased free-T4 fraction in serum. Furosemide competes for T4-binding sites on TBG, prealbumin, and albumin, so that a single high dose can acutely lower the total T4 level. Phenytoin and carbamazepine reduce serum protein binding of thyroid hormones, and total and FT4 may be reduced by 20% to 40%, but most patients have normal serum TSH levels and are clinically euthyroid. Closely monitor thyroid hormone parameters. |
Table 3: Drugs That May Alter Hepatic Metabolism of Thyroid hormones
| Potential impact: Stimulation of hepatic microsomal drug-metabolizing enzyme activity may cause increased hepatic degradation of thyroid hormones, resulting in increased CYTOMEL requirements. | |
| Drug or Drug Class | Effect |
| Phenobarbital Rifampin |
Phenobarbital has been shown to reduce the response to thyroxine. Phenobarbital increases L-thyroxine metabolism by inducing uridine 5'-diphospho-glucuronosyltransferase (UGT) and leads to a lower T4 serum levels. Changes in thyroid status may occur if barbiturates are added or withdrawn from patients being treated for hypothyroidism. Rifampin has been shown to accelerate the metabolism of thyroid hormones. |
Table 4: Drugs That May Decrease Conversion of T4 to T3
| Potential impact: Administration of these enzyme inhibitors decreases the peripheral conversion of T4 to T3, leading to decreased T3 levels. However, serum T4 levels are usually normal but may occasionally be slightly increased. | |
| Drug or Drug Class | Effect |
| Beta-adrenergic antagonists (e.g., Propranolol >160 mg/day) | In patients treated with large doses of propranolol (>160 mg/day), T3 and T4 levels change, TSH levels remain normal, and patients are clinically euthyroid. Actions of particular beta-adrenergic antagonists may be impaired when a hypothyroid patient is converted to the euthyroid state. |
| Glucocorticoids (e.g., Dexamethasone ≥4 mg/day) | Short-term administration of large doses of glucocorticoids may decrease serum T3 concentrations by 30% with minimal change in serum T4 levels. However, long-term glucocorticoid therapy may result in slightly decreased T3 and T4 levels due to decreased TBG production (see above). |
| Other drugs: Amiodarone | Amiodarone inhibits peripheral conversion of levothyroxine (T4) to triiodothyronine (T3) and may cause isolated biochemical changes (increase in serum free-T4, and decreased or normal free-T3) in clinically euthyroid patients. |
Antidiabetic Therapy
Addition of CYTOMEL therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements. Carefully monitor glycemic control, especially when CYTOMEL is started, changed, or discontinued [see WARNINGS AND PRECAUTIONS].
Oral Anticoagulants
CYTOMEL increases the response to oral anticoagulant therapy. Therefore, a decrease in the dose of anticoagulant may be warranted with correction of the hypothyroid state or when the CYTOMEL dose is increased. Closely monitor coagulation tests to permit appropriate and timely dosage adjustments.
Digitalis Glycosides
CYTOMEL may reduce the therapeutic effects of digitalis glycosides. Serum digitalis glycoside levels may be decreased when a hypothyroid patient becomes euthyroid, necessitating an increase in the dose of digitalis glycosides.
Antidepressant Therapy
Concurrent use of tricyclic (e.g., amitriptyline) or tetracyclic (e.g., maprotiline) antidepressants and CYTOMEL may increase the therapeutic and toxic effects of both drugs, possibly due to increased receptor sensitivity to catecholamines. Toxic effects may include increased risk of cardiac arrhythmias and central nervous system stimulation. CYTOMEL may accelerate the onset of action of tricyclics. Administration of sertraline in patients stabilized on CYTOMEL may result in increased CYTOMEL requirements.
Ketamine
Concurrent use of ketamine and CYTOMEL may produce marked hypertension and tachycardia. Closely monitor blood pressure and heart rate in these patients.
Sympathomimetics
Concurrent use of sympathomimetics and CYTOMEL may increase the effects of sympathomimetics or thyroid hormone. Thyroid hormones may increase the risk of coronary insufficiency when sympathomimetic agents are administered to patients with coronary artery disease.
Tyrosine-Kinase Inhibitors
Concurrent use of tyrosine-kinase inhibitors such as imatinib may cause hypothyroidism. Closely monitor TSH levels in such patients.
Drug-Laboratory Test Interactions
Consider changes in TBG concentration when interpreting T4 and T3 values. Measure and evaluate unbound (free) hormone in this circumstance. Pregnancy, infectious hepatitis, estrogens, estrogencontaining oral contraceptives, and acute intermittent porphyria increase TBG concentrations. Nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, androgens and corticosteroids decrease TBG concentration. Familial hyper- or hypo-thyroxine binding globulinemias have been described, with the incidence of TBG deficiency approximating 1 in 9000.
Read the entire FDA prescribing information for Cytomel (Liothyronine Sodium)
© Cytomel Patient Information is supplied by Cerner Multum, Inc. and Cytomel Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.
Health Solutions From Our Sponsors