Common Uses:Off Label Uses:Side Effects:
Adverse reactions associated with Novothyrox or levothyroxine therapy are primarily those of hyperthyroidism due to therapeutic overdosage. 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;

Cardiovascular: palpitations, tachycardia, arrythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest;

Respiratory: dyspnea;

Gastrointestinal: diarrhea, vomiting, abdominal cramps and elevations in liver function tests;

Dermatologic: hair loss, flushing;

Endocrine: decreased bone mineral density;

Reproductive: menstrual irregularities, impaired fertility.

Pseudotumor cerebri and slipped capital femoral epiphysis have been reported in children receiving levothyroxine therapy. Overtreatment may result in craniosynostosis in infants and premature closure of the epiphyses in children with resultant compromised adult height.

Seizures have been reported rarely with the institution of levothyroxine therapy.

Inadequate levothyroxine dosage will produce or fail to ameliorate the signs and symptoms of hypothyroidism.

Hypersensitivity reactions to inactive ingredients have occurred in patients treated with thyroid hormone products. These include urticaria, pruritus, skin rash, flushing, angioedema, various GI symptoms (abdominal pain, nausea, vomiting and diarrhea), fever, arthralgia, serum sickness and wheezing. Hypersensitivity to levothyroxine itself is not known to occur.

Cautions / Warnings:Drug Interactions:
Many drugs affect thyroid hormone pharmacokinetics and metabolism (e.g., absorption, synthesis, secretion, catabolism, protein binding, and target tissue response) and may alter the therapeutic response to Novothyrox. In addition, thyroid hormones and thyroid status have varied effects on the pharmacokinetics and actions of other drugs.

The various drug interactions with Novothyrox are as described below:

Drugs that may reduce TSH secretion – the reduction is not sustained; therefore, hypothyroidism does not occur:
• Dopamine/Dopamine
• Agonists
• Glucocorticoids
• Octreotide
Use of these agents may result in a transient reduction in TSH secretion when administered at the following doses: Dopamine ( ≥ 1 mcg/kg/min); Glucocorticoids (hydrocortisone ≥ 100 mg/day or equivalent); Octreotide ( > 100 mcg/day).

Drugs that alter thyroid hormone secretion
Drugs that may decrease thyroid hormone secretion, which may result in hypothyroidism
• Aminoglutethimide
• Amiodarone
• Iodide (including iodine-containing Radio-graphic contrast agents)
• Lithium
• Methimazole
• Propylthiouracil (PTU) Sulfonamides
Drugs that may increase thyroid hormone secretion, which may result in hyperthyroidism
• Amiodarone
• Iodide
Drugs that may decrease T4 absorption, which may result in hypothyroidism
• Antacids
• Aluminum & Magnesium Hydroxides
• Simethicone Bile Acid Sequestrants
• Cholestyramine
• Colestipol
• Calcium Carbonate
• Cation Exchange Resins
• Kayexalate
• Ferrous Sulfate
• Orlistat
• Sucralfate
Drugs that may alter T4 and T3 serum transport – but FT4 concentration remains normal; and, therefore, the patient remains euthyroid
Drugs that may increase serum TBG concentration Drugs that may decrease serum TBG concentration
• Clofibrate
• Estrogen-containing oral contraceptives
• Estrogens (oral)
• Heroin/Methadone
• 5-Fluorouracil
• Mitotane
• Tamoxifen Androgens/Anabolic Steroids
• Asparaginase
• Glucocorticoids
• Slow-Release Nicotinic Acid
Drugs that may alter T4 and T3 metabolism
Drugs that may increase hepatic metabolism, which may result in hypothyroidism
• Carbamazepine
• Hydantoins
• Phenobarbital
• Rifampin
Drugs that may decrease T4 5'-deiodinase activity
• Amiodarone
• Beta-adrenergic antagonists (e.g., Propranolol > 160 mg/day)
• Glucocorticoids (e.g., Dexamethasone ≥ 4 mg/day)
• Propylthiouracil (PTU)
Miscellaneous
Anticoagulants (oral)
Coumarin Derivatives
Indandione Derivatives
Antidepressants- Tricyclics (e.g., Amitriptyline)
Tetracyclics (e.g., Maprotiline)
Selective Serotonin Reuptake Inhibitors (SSRIs; e.g.,Sertraline)
Antidiabetic Agents
Biguanides
Meglitinides
Sulfonylureas
Thiazolidediones

Insulin Addition of levothyroxine to antidiabetic or insulin therapy may result in increased antidiabetic agent or insulin requirements. Careful monitoring of diabetic control is recommended, especially when thyroid therapy is started, changed, or discontinued.

Cardiac Glycosides Serum digitalis glycoside levels may be reduced in hyperthyroidism or when the hypothyroid patient is converted to the euthyroid state. Therapeutic effect of digitalis glycosides may be reduced.

Cytokines
- Interferon-α
- Interleukin-2
Therapy with interferon-q has been associated with the development of antithyroid microsomal antibodies in 20% of patients, and some have transient hypothyroidism, hyperthyroidism, or both. Patients who have antithyroid antibodies before treatment are at higher risk for thyroid dysfunction during treatment. Interleukin-2 has been associated with transient painless thyroiditis in 20% of patients. Interferon-β and –γ have not been reported to cause thyroid dysfunction.

Growth Hormones
- Somatrem
- Somatropin
Excessive use of thyroid hormones with growth hormones may accelerate epiphyseal closure. However, untreated hypothyroidism may interfere with growth response to growth hormone.

Ketamine Concurrent use may produce marked hypertension and tachycardia; cautious administration to patients receiving thyroid hormone therapy is recommended.

Methylxanthine Bronchodilators - (e.g., Theophylline) Decreased theophylline clearance may occur in hypothyroid patients; clearance returns to normal when the euthyroid state is achieved.

Radiographic Agents Thyroid hormones may reduce the uptake of 123I, 131I, and 99mTc.

Sympathomimetics: Concurrent use 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.

Chloral Hydrate
Diazepam
Ethionamide
Lovastatin
Metoclopramide
6-Mercaptopurine
Nitroprusside
Para-aminosalicylate
sodium
Perphenazine
Resorcinol (excessive topical use)
Thiazide Diuretics: These agents have been associated with thyroid hormone and/or TSH level alterations by various mechanisms.