Levothyroxine Wikipedia

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Levothyroxine Wikipedia

Atrial fibrillation is the most common of the arrhythmias observed with levothyroxine overtreatment in the elderly. Over-treatment with levothyroxine may cause an increase in heart rate, cardiac wall thickness, and cardiac contractility and may precipitate angina or arrhythmias, particularly in patients with cardiovascular disease and in elderly patients. Initiate SYNTHROID therapy in this population at lower doses than those recommended in younger individuals or in patients without cardiac disease see DOSAGE AND ADMINISTRATION and Use In Specific Populations. The recommended starting daily dosage of SYNTHROID in adults with primary, secondary, or tertiary hypothyroidism is based on age and comorbid cardiac conditions, as described in Table 1.

Antidepressant Therapy

You may not be able to take Synthroid if you have certain medical conditions. Tell your doctor if you have an untreated or uncontrolled adrenal gland disorder, a thyroid disorder called thyrotoxicosis, or if you have any recent or current symptoms of a heart attack. Levothyroxine sodium should be reduced in dose or temporarily discontinued if signs or symptoms of overdosage occur. Treated children may manifest a period of catch-up growth, which may be adequate in some cases to normalize adult height. In children with severe or prolonged hypothyroidism, catch-up growth may not be adequate to normalize adult height.

Thyroid hormones cross the placental barrier to some extent as evidenced by levels in cord blood of athyreotic fetuses being approximately one-third maternal levels. Transfer of thyroid hormone from the mother to the fetus, however, may not be adequate to prevent in utero hypothyroidism. Changes in TBG concentration must be considered when interpreting T4 and T3 values, which necessitates measurement and evaluation of unbound (free) hormone and/or determination of the free T4 index (FT4I). Pregnancy, infectious hepatitis, estrogens, estrogen-containing oral contraceptives, and acute intermittent porphyria increase TBG concentrations.

PRECAUTIONS

Closely monitor coagulation tests to permit appropriate and timely dosage adjustments. SYNTHROID is indicated in adult and pediatric patients, including neonates, as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer. Overtreatment or undertreatment with levothyroxine may have negative effects on different systems throughout the human body. So, my job as a thyroid specialist in these patients is to make sure my patient is treated and gets to a point of consistency, because it is a lifelong course of medication. Since thyroid hormone occurs naturally in the body, almost anyone can take levothyroxine.

Follow your doctor’s dosing instructions and try to take the medicine at the same time each day. Follow all directions on your prescription label and read all medication guides or instruction sheets. To this day, thyroxine, familiarly known by the trade name Synthroid (Abbvie, North Chicago, IL), is the second most prescribed drug in the United States. Administer SYNTHROID as a single daily dose, on an empty stomach, one-half to one hour before breakfast. Pregnant and lactating females need to discuss the dose and use of this medication with their caregivers. This document does not contain all possible side effects and others may occur.

Activated charcoal or cholestyramine may also be used to decrease absorption. Central and peripheral increased sympathetic activity may be treated by administering β-receptor antagonists, e.g., propranolol, provided there are no medical contraindications to their use. Provide respiratory support as needed; control congestive heart failure and arrhythmia; control fever, hypoglycemia, and fluid loss as necessary. Large doses of antithyroid drugs (e.g., methimazole or propylthiouracil) followed in one to two hours by large doses of iodine may be given to inhibit synthesis and release of thyroid hormones. Glucocorticoids may be given to inhibit the conversion of T4 synthroid derived to T3. Plasmapheresis, charcoal hemoperfusion and exchange transfusion have been reserved for cases in which continued clinical deterioration occurs despite conventional therapy.

DRUG INTERACTIONS

For patients at risk of atrial fibrillation or patients with underlying cardiac disease, start with a lower dosage and titrate the dosage more slowly to avoid exacerbation of cardiac symptoms. Dosage titration is based on serum TSH or free-T4 see Important Considerations For Dosing. HypothyroidismSYNTHROID® (levothyroxine sodium) tablets, for oral use is indicated as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. So, as a reminder, SYNTHROID is indicated for the treatment of hypothyroidism. That is primary, secondary, or tertiary hypothyroidism, either due to congenital or acquired state.

Pediatric Dosage – Congenital or Acquired Hypothyroidism

The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues. Consider changes in TBG concentration when interpreting T4 and T3 values. Measure and evaluate unbound (free) hormone and/or determine the free-T4 index (FT4I) in this circumstance. Pregnancy, infectious hepatitis, estrogens, estrogen-containing oral contraceptives, and acute intermittent porphyria increase TBG concentration.

Adverse Reactions

Absorption of orally administered T4 from the gastrointestinal tract ranges from 40% to 80%. The majority of the SYNTHROID dose is absorbed from the jejunum and upper ileum. T4 absorption is increased by fasting, and decreased in malabsorption syndromes and by certain foods such as soybeans.

  • Adequacy of therapy should be assessed by measuring serum free- T4 levels, which should be maintained in the upper half of the normal range in these patients.
  • The synthetic T4 in SYNTHROID is identical to that produced naturally by the human thyroid gland.
  • Undertreatment may result in poor school performance due to impaired concentration and slowed mentation and in reduced adult height.
  • When the optimum replacement dose has been attained, clinical (physical examination) and biochemical monitoring may be performed every 6-12 months, depending on the clinical situation, and whenever there is a change in the patient’s status.

Acute Adrenal Crisis In Patients With Concomitant Adrenal Insufficiency

If the T4 and TSH levels are normal, euthyroidism may be assumed and, therefore, the hypothyroidism can be considered to have been transient. In this instance, however, the physician should carefully monitor the child and repeat the thyroid function tests if any signs or symptoms of hypothyroidism develop. In this setting, the clinician should have a high index of suspicion of relapse. If the results of the levothyroxine withdrawal test are inconclusive, careful follow-up and subsequent testing will be necessary. Circulating thyroid hormones are greater than 99% bound to plasma proteins, including thyroxine-binding globulin (TBG), thyroxine-binding prealbumin (TBPA), and albumin (TBA), whose capacities and affinities vary for each hormone. The higher affinity of both TBG and TBPA for T4 partially explains the higher serum levels, slower metabolic clearance, and longer half-life of T4 compared to T3.