Chapter 31: Throid/ Antithyroid Drugs Flashcards
Hyperthyroidism
Severe form is called thyrotoxicosis
Thyroid stimulating hormone (TSH)
An endogenous hormone secreted by the pituitary gland and controls the release of the thyroid gland hormones necessary for its growth
Thyroxine (T4)
Principle thyroid hormone influencing metabolic rate
Triiodothyronine (T3)
Secondary thyroid hormone that also affects body metabolism
Thyroid gland function
Secretes 3 hormones: T3, T4, and calcitonin
Communicate with parathyroid glands that are made up of cells responsible for maintaining adequate levels of calcium in the extra cellular fluid, primarily by mobilizing calcium from bone
Process of producing T3 and T4 in the thyroid gland
Iodide is needed for this and is acquired from the diet
1mg is needed per week and is absorbed from the blood and then sequestered by the thyroid gland where it’s concentrated to 20x it’s blood level
It is also converted to iodine which is combined with tyrosine to make diiodotyrosine causing the formation of thyroxine which has four molecules=T4. Coupling of one diiodotyrosine molecule and and one molecule of monoiodotyrosine= T3.
Biological potency of T3 is about 4x greater than T4.
After T3 and T4 are synthesized, they are
Stored in the follicles in the thyroid glands in a complex with thyroglobulin (tyrosine and amino acid protein) called colloid. Then thyroglobulin is broken down to release T3 and T4 into the circulation when stimulated by the thyroid gland.this process is triggered by TSH (or thyrotropin) and released from the anterior pituitary gland when blood levels of T3 and T4 are low
Thyroid hormones:
Regulate the nasal metabolic rate and lipid and carb metabolism; are essential for normal growth and development; control the heat regulating system (thermoregulatory center in the brain); and have various effects on the CV, endocrine, and neuromuscular systems
Primary hypothyroidism
An abnormality in the thyroid gland itself. Occurs when the thyroid gland is not able to perform one of its functions
Most common type
Secondary hypothyroidism
Begins at the level of the pituitary gland and results from reduced secretion of TSH which is needed to trigger T3 and T4 release that are stored in the thyroid gland
Tertiary hypothyroidism
Caused by a reduced level of the thyrotropin releasing hormone from the hypothalamus which reduces TSH and thyroid hormone levels
Hypothyroidism S/S
Cold intolerance, unintentional weight gain, depression, dry brittle hair and nails, and fatigue
Hypothyroidism during youth
Can lead to cretinism (characterized by a low metabolic rate, retarded growth and sexual development, possible mental retardation)
Hypothyroidism as an adult
May lead to myxedema (characterized by decreased metabolic rate, involves loss of mental and physical stamina, weight gain, hair loss, firm edema, and yellow fullness of the skin
Hypothyroidism May result in
Goiter formation (enlarged thyroid gland from overstimulated TSH levels, TSH levels are overstimulated because there is little to no thyroid hormone in the circulation)
Drugs causing hypothyroidism
Amiodarone is the most common
Can also cause hyperthyroidism
Hyperthyroidism can be caused by different diseases including
Graves’ (most common), and Plummer’s Disease (also known as toxic nodular disease) which is the least common cause
Thyroid storm
Severe and life-threatening exacerbation of the S/S of hyperthyroidism that is usually induced by stress or infection
Hyperthyroidism S/S
Diarrhea, flushing, increased appetite, muscle weakness, fatigue, palpitations, irritability, nervousness, sleep disorders, heat intolerance, and altered menstrual flow.
Natural Thyroid replacement drugs
Derived from the thyroid glands of animals such as cattle and hogs
Only currently one: thyroid/ thyroid desiccated (refers to the drying process used to prepare the drug)
All natural peeps are standardized for their iodine content
Synthetic thyroid replacement drugs
Preparations include T3, T4, and liotrix (combo of T3, T4, in a 1:4 ratio)
Thyroid replacements dosing
Determined by the appropriate monitoring of serum TSH and free thyroid hormone levels
Thyroid drugs MOA
Cellular level- induce changes in the metabolic rate (rate of protein, carbs, and lipid metabolism), increase O2 consumption, body temp., blood volume, and overall cellular growth and differentiation. Stimulate CV system by increasing the number of myocardial beta-adrenergic receptors increasing the sensitivity of the heart to catecholamines and ultimately increases cardiac output
Also increased renal blood flow and the glomerular filtration rate resulting in a diuretic effect
Thyroid preparations indications
Replace what the thyroid gland cannot produce to achieve normal thyroid hormone levels
Can be used to diagnose suspected hyperthyroidism and prevent/treat footers
Replace hormones in patients whose thyroid glands have been surgically removed or destroyed by radioactive iodine in the treatment of thyroid cancer or hyperthyroidism
Hypothyroidism during pregnancy is treated with dose adjustments every 4 weeks to maintain TSH levels at the lower end of the normal range; fetal growth may be retarded if maternal hypothyroidism remains untreated during pregnancy
Thyroid preparation contraindications
Drug allergy, recent MI, adrenal insufficiency, and hyperthyroidism
Adverse effects of thyroid medications
Usually the result of overdose
Most significant: cardiac dysrhythmias with the risk of life-threatening or fatal irregularities
Other more common, less toxic include:
Tachycardia, palpitations, angina, hypertension
Insomnia, tremors, HA, anxiety
Nausea, diarrhea, cramps
Menstrual irregularities, wt. loss, sweat, fever, heat intolerance
Thyroid drug interactions
Phenytoin and Fosphenytoin cause reduced levothyroxine effectiveness
Cholestyramine, antacids, calcium salts, iron, and estrogen cause reduced levothyroxine effectiveness
Warfarin causes increased warfarin effects
May enhance the activity of oral anticoagulants
Chilestyramine binds to thyroid hormone in the GI tract possibly reducing absorption of both drugs
Thyroid drugs
Synthetic drugs (levothyroxine and liotrix) are common
T3, T4, cost, duration of effect should be considered before drug therapy initiation
Classified as pregnancy category A drugs
Levothyroxine
Most commonly prescribed synthetic thyroid hormone (“drug of choice”)
Chemically pure: 100% T4 making it more predictable than other thyroid preparations; it’s half-life is long enough that it only needed to be administered once a day
Oral (should be taken every morning 30-60 minutes before food; tube feedings can impair absorption) and parenteral forms
DO NOT SWITCH BRANDS: can destabilize course of treatment; monitor thyroid function tests
Dose in micrograms; doses higher than 200 mcg should be questioned in case of a mcg- mg error
IV form (50% of oral dose): remember to dilute FIRST, then the dose is calculated upon the concentration of the reconstituted medication, not the size of the vial.
Anti thyroid drugs
Aimed to treat the primary cause of the disease or S/S of the disease
Also known as thioamide derivatives and include methimazole and propylthiouracil (PTU)
Radioactive iodine (destroys the thyroid gland- ablation; commonly used to Tx hyperthyroidism and thyroid cancer) and potassium iodine (prophylaxis for radiation exposure) may also be used to treat hyperthyroidism
Antithyroid MOA
Methimazole and PTU inhibit incorporation of iodine molecules into the amino acid tyrosine (process required to make T3 and T4) = these drugs then impede the formation of thyroid hormone
PTU inhibits the conversion of T4 to T3 in the peripheral circulation
Neither drug can inactivate the already existing thyroid hormone
Overall effect: decrease in thyroid hormone levels, normalizing overall metabolic rate
Anti thyroid indications
Tx hyperthyroidism and prevent the surge in thyroid hormones that occurs after the surgical treatment of or during radioactive iodine therapy for hyperthyroidism or thyroid cancer
Long term administration (several years) may induce a spontaneous remission (e.g., seen in Graves’ disease)
Surgical resection of the thyroid gland (thyroidectomy) is often used in patients who are intolerant to antithyroid therapy and in pregnant women that antithyroid and radioactive iodine therapy is contraindicated
antithyroid Contraindications
Drug allergy, use in pregnancy (category D) although is sometimes necessary
The FDA: PTU is to be used in 1st tri only, and methimazole is used for the remainder (reports of scalp abnormalities in fetus with methimazole use)
Pregnant patient treatment is physician specific
Antithyroid Adverse Effects
Most damaging/serious: liver and bone marrow toxicity
More common, less toxic: Drowsy, HA, vertigo, paresthesia N/V, diarrhea, hepatitis, loss of taste Smoky urine, decreased urine output Agranulocytosis, leukopenia, thrombocytopenia, hypothrombinemia, lymphadenopathy, bleeding Rash, pruritis Myalgia, arthralgia Increased blood urea nitrogen and serum creatinine levels Enlarged thyroid glands, nephritis
Antithyroid interactions
Additive leucopenic effects when taken in conjunction with other bone marrow suppressants and an increase in the activity of oral anticoagulants
Propylthiouracil drug profile
This is a thioamide antithyroid drug
About 2 weeks of therapy may be necessary before therapeutic effects begin
Only oral 50 mg tabs
Methimazole is the only alternative and is rarely used clinically
Thyroid replacement drugs: assessment
Include baseline VS, T3, T4, TSH, and doc any past and present medical problems or concerns
Review baseline VS with attention to Hx of cardiac dysrhythmias because of drug-related effects of cardiac irregularities; these dysrhythmias may be life threatening
Female patients: assess impact of thyroid hormones on the reproductive system
Older adults: may have increased sensitivity to thyroid replacement effects; report palpitations, CP, stumbling, falling, depression, incontinence, sweating, SOB, aggravated heart disease, cold intolerance, wt. gain
Different patients may respond different to the same drug/dose
Antithyroid drug assessments
Assess VS and S/S of thyroid crisis or thyroid storm (precipitating causes include stress or infection)
Levothyroxine pharmacokinetics
Onset of action: 3-5 days
Peak plasma concentrations: within 24 hours
Half life: 6-10 days
Duration of action: 24 hours
Prolonged half life= increased risk for toxicity (wt. loss, tachycardia, nervousness, tremors, hypertension, HA, insomnia, menstrual irregularities, and cardiac irregularities or palpitations.
Highly protein bound (similar to a sustained release drug)= remains in body longer, increased risk for interactions with other protein binding drugs and increase the potential for toxicity
Thyroid replacement drug implementations
Given at the same time every day to help maintain consistent blood levels of the drug
Best to take once daily as prescribed
Take in am on empty stomach about 39 minutes before breakfast
Taking in afternoon/evening will lead to sleepiness
Avoid taking OTC antacids, iodine, vitamins, or supplements containing iron/ calcium within a 4 hour time frame
Iodized salt and iodine rich foods (soybeans, tofu, seafood, some breads) must be avoided
Avoid interchanging replacement brands because of possible differences in their bio equivalence from various manufacturers
May crush if needed
For radioactive iodine isotope studies (thyroid uptake and scan) the thyroid drug is usually discontinued about 4 weeks before the test (only as prescribed)
Older adults: may require alteration of the dose amount with a decrease of up to 25% for patients 69 years and older
Antithyroid implementations
Take with meals to decrease GI upset
Report fever, sore throat, mouth sores or ulcers, skin eruptions, unusual bruising or bleeds (may indicate liver/bone toxicity with possible leukopenia)
Monitor liver function tests and CBC counts
Avoid iodized salts or shellfish because of their potential for altering the drugs effectiveness
Advise patients to be aware of S/S of hypothyroidism: unexplained wt. gain, loss of mental and physical stamina, hair loss, firm edema, and yellow fullness of the skin (Indicative of myxedema or a decrease in metabolic rate)
Thyroid replacement drugs evaluations
Decrease is S/S of hypothyroidism
Improved energy levels, mental stamina, and physical stamina
Clues of possible inadequate doses: return of hypothyroidism S/S
Antithyroid medications evaluations
Return to normal status with little or no evidence of hyperthyroid
Clues of inadequate dosing: continued hyperthyroidism S/S
Thyroid replacement patient teachings
Best taken 1/2-1 hour before breakfast on an empty stomach to enhance their absorption orally and to maintain hormone levels
Sleepiness can be prevented by taking Ned in morning
Not to be abruptly discontinued
Follow ups are significant
Brands can not be interchanged
Provide S/S to look for and to report
Take with 6-8 oz of water
Report CP, wt. loss, palpitations, tremors, sweat, nervousness, SOB, insomnia because these may indicate toxicity
Encourage journal use
May take weeks to see therapeutic effects
Keep tablets protected from the light
Antithyroid patient teachings
Better tolerated with meals or snack
Never to be withdrawn abruptly
Avoid eating foods high in iodine such as tofu, and other soy products, turnips, seafood, iodized salts, and some breads because they may interfere with the effectiveness of the antithyroid drugs
