Source: Jonklaas J, Talbert RL.
Thyroid Disorders. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR,
Wells BG, Posey LM, eds. Pharmacotherapy:
A Pathophysiologic Approach. 8th ed. http://accesspharmacy.com/content.aspx?aid=7991868.
Accessed June 22, 2012.
- Clinical and biochemical syndrome resulting from decreased
thyroid hormone production.
- Hashimoto's disease
- Iatrogenic hypothyroidism
- Iodine deficiency
- Enzyme defects
- Thyroid hypoplasia
- Pituitary disease
- Hypothalamic disease
- Most patients have primary hypothyroidism due to thyroid
gland failure from chronic autoimmune thyroiditis (Hashimoto’s
- Defects in suppressor T-lymphocyte function lead to survival
of mutating clone of helper T lymphocytes that produce thyroid antibodies.
- Iatrogenic hypothyroidism follows exposure to excessive amounts
of radiation (radioiodine or external radiation) or after total
- Other causes of primary hypothyroidism include:
- Enzymatic defects within thyroid gland
- Thyroid hypoplasia
- Maternal ingestion of goitrogens during fetal development
- Secondary hypothyroidism may be due to:
insufficiency because of pituitary tumors
- Surgical therapy
- External pituitary radiation
- Postpartum pituitary necrosis
- Infiltrative processes (e.g., metastatic tumors, tuberculosis)
- Occurs in 1.5–2% of women and 0.2% of
- Incidence increases with age.
- Postpartum status
- Family history of autoimmune thyroid disorders
- Previous head, neck, or thyroid irradiation or surgery
- Autoimmune endocrine conditions, including:
- Dry skin
- Cold intolerance
- Weight gain
- Muscle cramps
- Loss of ambition or energy
- Coarse skin and hair
- Cold or dry skin
- Periorbital puffiness
- Slowed or hoarse speech
- Proximal muscle weakness
- Slow relaxation of deep tendon reflexes
- In primary hypothyroidism, thyroid-stimulating hormone
- In secondary hypothyroidism, TSH levels may be within or below
- Free and/or total thyroxine (T4)
and triiodothyronine (T3) serum concentrations low.
- Antithyroid peroxidase antibodies and anti-TG antibodies often
elevated in autoimmune thyroiditis.
- Chronic fatigue syndrome
- Congestive heart failure
- Anemia due to other causes
- Restore thyroid hormone concentrations in tissue.
- Provide symptomatic relief.
- Prevent neurologic deficits in newborns and children.
- Reverse biochemical abnormalities.
- Table 1. Thyroid preparations used for treatment of hypothyroidism.
drug of choice for thyroid hormone replacement therapy.
- Once product selected, therapeutic interchange discouraged.
- Starting dose for young patients with longstanding disease
and patients older than 45 years without known cardiac disease 50
mcg daily, increased to 100 mcg daily after 1 month.
- Recommended initial dose for older patients or those with
known cardiac disease 25 mcg/day, titrated upward in increments
of 25 mcg monthly.
- Individualize dose with appropriate TSH monitoring; average
maintenance dose ~125 mcg/day.
- Drug interactions
- Oral absorption may be impaired
- Calcium carbonate
- Aluminum hydroxide
- Ferrous sulfate
- Fiber supplements
- Increased clearance may occur with:
- Amiodarone may block conversion of T4 to T3.
- Thyroid, USP (desiccated thyroid)
from animal glands and may be antigenic.
- Inexpensive generic brands may not be bioequivalent.