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Thyroid&
Antithyroid Drugs
By M. H. Farjoo M.D, Ph.D.Shahid Beheshti University of Medical Science
Thyroid & Antithyroid Drugs
Introduction Drugs in Hypothyroidism Drugs in Hyperthyroidism Adjuncts to Antithyroid
Therapy Thyroid malfunction and
Pregnancy Neonatal Graves' Disease Drug Pictures
Introduction Thyroid releases T3 & T4
The ratio of T4 to T3 is 5:1, so most of the hormone released is thyroxine
Most of the T3 in the blood is derived from thyroxine
T3 is three to four times more potent than T4
The affinity of the receptor site for T3 is about ten times higher than that for T4
Drugs in Hypothyroidism
Levothyroxine is the choice drug for hypothyroidism
T4 is converted to T3 intracellularly so levothyroxine produces both hormones
If angina pectoris or cardiac arrhythmia develops, it is essential to stop thyroxine immediately
Drugs in Hyperthyroidism
The antithyroid compounds include: Thioamides
Methimazole Propylthiouracil
Iodides Radioactive iodine
Thioamides
Their major action is blocking iodine organification Since the synthesis of hormones is affected, their
effect requires 4 weeks Propylthiouracil is preferable in pregnancy:
It crosses the placenta less readily Is not secreted in breast milk
The most common adverse effect is a maculopapular pruritic rash
The most dangerous complication is reversible agranulocytosis
Iodide
Iodides can induce hyperthyroidism (jodbasedow phenomenon) or precipitate hypothyroidism
In pharmacologic doses the major action is to inhibit hormone release
Improvement in thyrotoxic symptoms occurs within 2–7 days (iodide therapy in thyroid storm)
Iodides in pregnancy should be avoided, since they cross the placenta and can cause fetal goiter
Radioactive Iodine
Women in the childbearing period should be treated with I131 or subtotal thyroidectomy prior to pregnancy
I131 should NOT be administered to pregnant or nursing women
I131 is the preferred treatment for patients over 21 years
Hypothyroidism occurs in 80% of patients by radioiodine
Adjuncts to Antithyroid Therapy
Hyperthyroidism resembles sympathetic overactivity
Propranolol, will control tachycardia, hypertension, and atrial fibrillation
Diltiazem, can control tachycardia in patients in whom beta-blockers are contraindicated
Barbiturates accelerate T4 breakdown (by enzyme induction) and are also sedative
Thyroid malfunction and Pregnancy
In a pregnant hypothyroid patient, it is extremely important that the dose of thyroxine be adequate.
This is because early development of the fetal brain depends on maternal thyroxine
If thyrotoxicosis occurs, propylthiouracil is used and an elective subtotal thyroidectomy performed
Neonatal Graves' Disease
Is either due to passage of TSH-R Ab [stim], or to genetic transmission of the trait
If caused by maternal TSH-R Ab [stim], the disease is self-limited and subsides over 4–12 weeks,
Treatment is necessary because of the severe metabolic stress of the infant
Therapy includes : propylthiouracil, Lugol's solution, propranolol and careful supportive therapy
Iodinates Contrast MediaGastrografin
Iodinates Contrast Mediaiodixanol
Iodinates Contrast Media iodixanol
Iodinates Contrast Media iodixanol
Iodinates Contrast Media iohexol
Iodinates Contrast Media iohexol
Iodinates Contrast Media iohexol
Iodinates Contrast Media iohexol
Iodinates Contrast Media iohexol
Iodinates Contrast Media iopromide
Iodinates Contrast Media iopromide
Iodinates Contrast Media iopromide
Iodinates Contrast Media Urografin
SummaryIn English
Thank youAny question?
Hypothyroidism
Hypothyroidism can occur with or without thyroid enlargement (goiter). The laboratory diagnosis of hypothyroidism in the adult is easily made by the combination of a low free thyroxine (or low free thyroxine index) and elevated serum TSH
Infants and children require more T4 per kilogram of body weight than adults
Chronic overtreatment with T4, particularly in elderly patients, can increase the risk of atrial fibrillation and accelerated osteoporosis
Myxedema Correction of myxedema must be done cautiously to
avoid provoking arrhythmia, angina, or acute myocardial infarction.
myxedema coma: It is associated with progressive weakness, stupor,
hypothermia, hypoventilation, hypoglycemia, hyponatremia, water intoxication, shock, and death
It is important to give all preparations intravenously The treatment of choice in myxedema coma is to give a
loading dose of levothyroxine intravenously— usually 300–400 µg initially, followed by 50 µg daily
Opioids and sedatives must be used with extreme caution
Hyperthyroidism The most common form of hyperthyroidism is
Graves' disease, or diffuse toxic goiter The three primary methods for controlling
hyperthyroidism are antithyroid drug therapy, surgical thyroidectomy, and destruction of the gland with radioactive iodine
Antithyroid Drug Therapy the more severe reaction of agranulocytosis is often
heralded by sore throat or high fever Thyroidectomy
A near-total thyroidectomy is the treatment of choice for patients with very large glands or multinodular goiters
Hyperthyroidism Toxic Uninodular Goiter & Toxic Multinodular
Goiter These forms of hyperthyroidism occur often in older
women with nodular goiters. FT4 is moderately elevated or occasionally normal, but T3 by RIA is strikingly elevated
Subacute Thyroiditis episodes of transient thyrotoxicosis have been termed
"spontaneously resolving hyperthyroidism." Supportive therapy is usually all that is necessary, such as propranolol for tachycardia and aspirin or nonsteroidal anti-inflammatory drugs to control local pain and fever
Special Problems
Ophthalmopathy elevation of the head to diminish periorbital edema
and artificial tears to relieve corneal drying. Smoking cessation should be advised to prevent progression of the ophthalmopathy
If steroid therapy fails or is contraindicated, irradiation of the posterior orbit, using well-collimated high-energy x-ray therapy, will frequently result in marked improvement of the acute process
Special Problems
Nontoxic Goiter The most common cause of nontoxic goiter
worldwide is iodide deficiency, but in the USA, it is Hashimoto's thyroiditis. Less common causes include dietary goitrogens, dyshormonogenesis, and neoplasms
Thyroid Neoplasms
Some adenomas will regress following thyroxine therapy; those that do not should be rebiopsied or surgically removed. Management of thyroid carcinoma requires a total thyroidectomy, postoperative radioiodine therapy in selected instances, and lifetime replacement with levothyroxine.
Class Mechanism of Action and Effects
Indications Pharmacokinetics, Toxicities, Interactions
Thyroid Preparations
Levothyroxine (T4 ) Activation of nuclear receptors results in gene expression with RNA formation and protein synthesis
Hypothyroidism maximum effect seen after 6–8 weeks of therapy
Liothyronine (T3)
Class Mechanism of Action and Effects
Indications Pharmacokinetics, Toxicities, Interactions
Antithyroid Agents Thioamides Propylthiouracil (PTU) Inhibit thyroid peroxidase
reactions block iodine organification inhibit peripheral deiodination of T4 and T3
Hyperthyroidism Oral duration of action: 6–8 h delayed onset of action Toxicity: Nausea, gastrointestinal distress, rash, agranulocytosis, hepatitis,hypothyroidism
Iodides Lugol solution Inhibit organification and
hormone release reduce the size and vascularity of the gland
Preparation for surgical thyroidectomy
Oral acute onset within 2–7 days Toxicity: Rare (see text)
Potassium iodide
Beta blockers Propranolol Inhibition of adrenoreceptors
inhibit T4 to T3 conversion (only propranolol)
Hyperthyroidism, especially thyroid storm adjunct to control tachycardia, hypertension, and atrial fibrillation
Onset within hours duration of 4–6 h (oral propranolol) Toxicity: Asthma, AV blockade, hypotension, bradycardia
Radioactive iodine 131I (RAI) Radiation destruction of
thyroid parenchymaHyperthyroidism patients should be euthyroid or on blockers before RAI avoid in pregnancy or in nursing mothers
Oral half-life 5 days onset of 6–12 weeks maximum effect in 3–6 months Toxicity: Sore throat, sialitis, hypothyroidism