Ch 58 Thyroid Drugs Flashcards
The thyroid gland produces two active hormones:
triiodothyronine (T3), which is highly active, and
thyroxine (T4, tetraiodothyronine), which appears inactive.
Thyroid hormones have three principal actions:
stimulation of energy use,
stimulation of the heart, and
promotion of growth and development.
Hormonal regulation of thyroid function occurs as follows:
TRH from the hypothalamus causes the pituitary to release TSH, which causes the thyroid to make and release T3 and T4, which then act on the pituitary to suppress further release of TSH.
The four steps in thyroid hormone synthesis are:
(1) uptake of iodide by the thyroid,
(2) conversion of iodide to iodine,
(3) linking of iodine to tyrosine, and
(4) coupling of two iodinated tyrosines to form T3 or T4.
Much of the T4 released by the thyroid is converted to __.
T3 in the periphery
Low plasma levels of iodine stimulate synthesis of ___.
T3 and T4
In iodine-sufficient countries, the major cause of hypothyroidism is __.
chronic autoimmune thyroiditis (Hashimoto’s thyroiditis)
A __ is an enlargement of the thyroid.
goiter
____ is the most sensitive way to diagnose hypothyroidism.
Testing serum for elevated levels of TSH
Most patients with hypothyroidism require ___.
lifelong replacement therapy with thyroid hormones
Maternal hypothyroidism during the first trimester of
pregnancy can result in __.
permanent neuropsychologic deficits in the child
___ is the drug of choice for most patients who require thyroid hormone replacement.
Levothyroxine (synthetic T4)
There is debate as to whether certain levothyroxine preparations are ___.
interchangeable.
Until the debate is resolved, it would seem best for patients to use only one product, unless the switch is approved of and monitored by the prescriber.
Levothyroxine should be taken __.
on an empty stomach in the morning, at least 30 to 60 minutes before eating
Chronic overtreatment with levothyroxine can cause (2).
atrial fibrillation and bone loss, especially in older adults
Many drugs—including cholestyramine [Questran],
colestipol [Colestid], sucralfate [Carafate], H2 receptor
blockers, proton pump inhibitors, aluminum-containing
antacids, iron supplements, and calcium supplements—can significantly reduce __.
levothyroxine absorption.
At least 4 hours should separate administration of levothyroxine and these drugs.
Levothyroxine can ___ of warfarin.
intensify the anticoagulant effects
Graves’ disease is the most common cause of __.
excessive thyroid hormone secretion
Graves’ disease can be treated by surgical removal of thyroid tissue, destruction of thyroid tissue with radioactive iodine (131I), or treatment with antithyroid drugs (2).
methimazole or propylthiouracil
__, an antithyroid drug, benefits patients with
hyperthyroidism by suppressing thyroid hormone
synthesis.
Methimazole
Full benefits of methimazole may take __.
3 to 12 weeks to develop
The most serious adverse effect of methimazole is __.
agranulocytosis
Methimazole should be avoided during __.
the first trimester of pregnancy
Methimazole is on the NIOSH hazardous drug list and
should be handled with caution by __.
healthcare workers of childbearing age
Full effects of 131I require __.
2 to 3 months to develop
Iodine-131 is contraindicated during __.
pregnancy and lactation
Strong iodine solution (Lugol’s solution) can be used to
__.
suppress thyroid hormone synthesis
