Important Safety Information

Precautions

Thyroid hormones should be used with great caution in a number of circumstances where the integrity of the cardiovascular system, particularly the coronary arteries, is suspected. These include patients with angina pectoris or the elderly, in whom there is a greater likelihood of acute cardiac disease. In these patients therapy should be initiated with low doses, i.e., 15-30mg NP Thyroid. When, in such patients, a euthyroid state can only be reached at the expense of an aggravation of the cardiovascular disease, thyroid hormone dosage should be reduced. Thyroid hormone therapy in patients with concomitant diabetes mellitus or diabetes insipidus or adrenal cortical insufficiency aggravates the intensity of their symptoms. Appropriate adjustments of the various therapeutic measures directed at these concomitant endocrine disease are required. The therapy of myxedema coma requires simultaneous administration of glucocorticoids. Hypothyroidism decreases and hyperthyroidism increases the sensitivity to oral anticoagulants. Prothrombin time should be closely monitored in thyroid treated patients on oral anticoagulants and dosage of the latter agents adjusted on the basis of frequent prothrombin time determinations. In infants, excessive doses of thyroid hormone preparations may produce craniosynostosis.

 

Drug Interactions

If you see more than one physician, be sure all of them are aware if you have been prescribed a thyroid medication and are also taking or have any of the following prescribed for you:
Amphetamines
Anticoagulants
Appetite suppressants
Medicine for asthma or other breathing problems
Medicines for colds, sinus problems, or hay fever or other allergies (including nose drops or sprays)

  • Oral Anticoagulants: Thyroid hormones appear to increase catabolism of vitamin K-dependent clotting factors. If oral anticoagulants are also being given, compensatory increases in clotting factor synthesis are impaired. Patients stabilized on oral anticoagulants who are found to require thyroid replacement therapy should be watched very closely when thyroid is started. If a patient is truly hypothyroid, it is likely that a reduction in anticoagulant dosage will be required. No special precautions appear to be necessary when oral anticoagulant therapy is begun in a patient already stabilized on maintenance thyroid replacement therapy.
  • Insulin or Oral Hypoglycemics Initiating thyroid replacement therapy may cause increases in insulin or oral hypoglycemic requirements:  The effects seen are poorly understood and depend upon a variety of factors such as dose and type of thyroid preparations and endocrinestatus of the patient. Patients receiving insulin or oral hypoglycemic should be closely watched during initiation of thyroid replacement therapy.
  • Chloestyramine: Cholestyramine binds both T4 and T3 in the intestine, thus impairing absorption of these thyroid hormones. In vitro studies indicate that the binding is not easily removed. Therefore four to five hours should elapse between administration of cholestyramine and  thyroid hormones.
  • Estrogen, Oral Contraceptives: Estrogens tend to increase serum thyroxinebinding globulin (TBg). In a patient with a nonfunctioning thyroid gland who is receiving thyroid replacement therapy, free levothyroxine may be decreased when estrogens are started thus increasing thyroid requirements. However, if the patient’s thyroid gland has sufficient function, the decreased free thyroxine will result in a compensatory increase in thyroxine output by the thyroid. Therefore, patients without a functioning thyroid gland who are on thyroid replacement therapy may need to increase their thyroid dose if estrogens or estrogen-containing oral contraceptives are given.

Adverse Reactions

Adverse reactions other than those indicative of hyperthyroidism because of therapeutic over dosage, either initially or during the maintenance period are rare.

Warnings

Drugs with thyroid hormone activity, alone or together with other therapeutic agents have been used for the treatment of obesity. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects. The use of thyroid hormone in the therapy of obesity, alone or combined with other drugs, is unjustified and has been shown to be ineffective. Neither is their use justified for the treatment of male or female infertility unless this condition is accompanied by hypothyroidism.

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