Drugs Affecting the Thyroid Flashcards
Hyper-function of endocrine glands indicate…
Tumors, excess stimulation → the patient is suspected to have a tumor until proven otherwise
Hypo-function of endocrine glands indicate…
Congenital defects/absence of gland or enzymes, destruction, age-related changes, receptor defects, lack of stimulation
Primary endocrine gland disorders
Dysfunction of gland or organ itself
Secondary endocrine gland disorders
Abnormal stimulation to gland
Thyroid gland
Vascular, two-lobed, surrounds trachea
Secretes T3, T4, and calcitonin in parafollicular cells
T3
Triiodothyronine (active form)
Contains 3 atoms of iodine
T4
Thyroxine (inactive form) Contains 4 atoms of iodine More T4 is produced than T3 T4 is converted to T3 Body's source of T3
The thyroid gland is regulated by…
TRH and TSH
Three principle actions of thyroid hormones
- Stimulation of energy use
- Stimulation of growth
- Promotion of growth and development
Thyroid hormones have profound impact on metabolism, cardiac function, growth and development
Conditions of the thyroid
- Hyperthyroidism
- Hypothyroidism
- Iodine deficiency
More than _____ of thyroid hormones are bound to protein.
99.5%
TSH lab test
- Appears to offer better discrimination for only a slightly higher cost
- TSH has become the standard of care as the single initial test of thyroid function
If serum TSH is within normal limits…
No further testing is required
If serum TSH is increased…
Free T4 level is then measured on the same initial sample to distinguish between overt and subclinical hypothyroidism
If serum TSH is suppressed…
Both serum T3 and T4 should be assessed off of the same initial sample to distinguish between overt thyrotoxicosis, T-3 toxicosis and subclinical thyrotoxicosis
The half-life of plasma TSH is…
- Approximately one hour
- Deviates more rapidly from the steady state
The half-life of plasma T4 is…
Approximately one week
Medications that influence TSH secretion
- T3 (triiodothyroacetic acid)
- Glucocorticoids
- Dopamine
- Amiodarone
- Amiodarone and Phenytoin (Dilantin) - tissue drug effects proportional to hormone concentration
Thyroid hormone replacement agents
- Levothyroxine (Synthroid, Levoxyl) = synthetic T4 (inactive form!)
- Dessicated thyroid = bovine (cow or pig hormone) & porcine T4 + T3
- Liothyronine (Cytomel, Triostat) = synthetic T3 (active form!)
- Liotrix (Euthroid) = synthetic T4 + T3 in 4:1 fixed ratio
Anti-thyroid agents
- Propylthiouracil (PTU)
- Methimazole (Tapazole)
Hypothyroidism
- May occur at any age
- Mild: Hypothyroidism
- Severe: Myxedema
Hypothyroidism in infancy is known as…
Cretinism
Clinical presentation of hypothyroidism
- Cold and dry skin
- Face is pale, puffy, and expressionless
- Hair is brittle and thin
- Heart rate and temperature are lowered
- Impaired mentation
- Patient may complain of lethargy, fatigue, and cold intolerance
Causes of hypothyroidism
- Malfunction of the thyroid gland
- Surgery
- Decreased iodine in diet
- Decreased secretion of TSH and TRH
