1. ANTITHYROID DRUGS
Thyroid
Fig 1 Fig 2
＊ Thyroid follicles are the structural & functional units of the thyroid gland.
＊ Each follicle is surround mainly by simple cuboidal epithelium and is
filled with a colloid which mainly composed by thyroglobulin.
＊ Thyroid hormones are mainly synthesized in colloid while the simple
cuboidal epithelium undertaking thyroglobulin production, iodide intake &
thyroid hormones release. 1

2. ●Synthesis of thyroid hormones
Thyroid hormones MIT: monoiodotyrosine
triiodothyronine (T3) DIT: diiodotyrosine
tetraiodothyronine (T4, thyroxine)
Materials
iodine & tyrosine Thioamid
e drugs
Steps
1. Iodide is trapped by sodium-iodide symporter
2. Iodide is oxidized by thyroidal peroxidase to iodine
3. Tyrosine in thyroglobulin is iodinated and forms MIT & DIT
4. Iodotyrosines condensation
MIT+DIT→T3; DIT+DIT→T4 2

3. ●Regulation of thyroid function
TRH: thyrotropin-releasing hormone
TSH: thyroid-stimulating hormone
3

4. ●Physiological actions of thyroid hormones
 To normalize growth and development, body
temperature, and energy levels
▲Insufficiency→ cretinism (infant & child), and
myxedema (adult);
▲Excess→hyperthyroid
 To enhance CNS excitability & sensitivity of CVS to NA
＃ T3 is 3 to 4 times more potent than T4 in heat
production;
＃ T4 in colloid is about 4 times more numerous than T3 ;
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5. hyperthyroid
cretinism
myxedema
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6. ●Mechanism of actions
of thyroid hormones
T3, via its nuclear
• Some of T4 are converted to receptor, induces
T3 in kidney and liver
new proteins
• The actions of T3 on several generation which
organ systems are shown
produce effects
• BMR: basal metabolic rate;
CNS: central nervous system
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7. Thyroid drugs
● Representative drugs
levothyroxine (L-T4, levoxyl, synthroid)
liothyronine (T3, cytomel, triostat)
liotrix (T4 plus T3) (euthyroid, thyrolar)
● Pharmacokinetics
po easily absorbed; the bioavailablity of T4 is 80%, and T3 is
95%.
Drugs that induce hepatic microsomal enzymes (e.g., rifampin,
phenbarbital, phenytoin, and etc) improve their metabolism. 7

8. ●Pharmacological effect
see physiological effect
● Clinical use
1. Hypothyroidism: cretinism & myxedema;
2. simple goiter: for pathogeny remaining unclear
(endemic goiter directly supply iodine)
3. Others:
● Adverse reactions
Overmuch leads to thyrotoxicosis;
Angina or myocardial infarction usually appears in
ageds
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9. Antithyroid drugs
● Drugs
Class Representative
propylthiouracil
methylthiouracil
Thioamides
methimazole
carbimazole
Iodides KI, NaI
Radioactive iodine 131
I
β-adrenoceptor blockers propranolol
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10. І. Thioamides
◆Structure
The thiocarbamide
group is essential for
antithyroid activity
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11. Pharmacological action
Inhibition of the synthesis of T3 & T4
Mechanism
All thioamides inhibit peroxidase-catalyzing reactions
Iodine organification First choice for
Iodotyrosines condensation thyroid crisis
Propylthiouracil also inhibit T4 converting to T3
Characteristics
① Result appears slowly: in 3-4 w hyperthyroid
ameliorated, and in 2-3 months BMR normalized;
② Long-term use leads to thyroid hyperplasia
③ Methimazole is 10 times as potent as propylthiouracil
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12. Clinical use
treatment of hyperthyroid
1. Mild hyperthyroid and those surgery & 131I
not permitted;
2. Operation preparation;
3. Thyroid crisis (comprehensive therapy).
Adverse reactions
1. Long-term use leads to thyroid hyperplasia;
2. Pruritic maculopapular rash is the most common
adverse raaction
3. The severe adverse reaction is agranulocytosis
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13. Iodides (NaI, KI)
Pharmacological action
Inhibition of T3 & T4 release and synthesis
Decrease of size & vascularity of the hyperplastic gland
Clinical use
Ministrant treatment of hyperthyroid
1. Operation preparation;
2. Thyroid crisis.
Adverse reactions
1. Acneiform rash (similar to that of bromism);
2. Swollen salivary glands, mucous membrane ulcerations, and etc.
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14. Radioactive iodine (131I)
131
I is the only isotope for treatment of thyrotoxicosis.
Its therapeutic effect depends on emission of β rays with an
effective half-life of 5 days & a penetration range of 0.4-2 mm.
Woman in pregnancy or lactation is forbidden!
β-adrenoceptor blockers
βblockers are effective in treatment of thyrotoxicosis.
Propranolol is the most widely studied and used.
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