Thyroid

Question 1

What is the treatment of choice for replacement therapy in hypothyroid patients

Answer 1

Levothyroxine (T4)

Long half life (7 days) and permits once daily to weekly administration

Question 2

What is a synthetic slat of T3

Answer 2

Liothyronine (T3) has shorter half life (24 H) requiring multiple daily doses, may have greater risk of cardiotoxicity** and more difficult to monitor

Question 3

Therapeutic uses of TH

Answer 3

1. Cretinism
2. Adult hypothyoidism
3. Myxedema coma
4. Nontoxic goiter

Question 4

What are the Rx pharmacologic measures

Answer 4

by inhibiting synthesis
by inhibiting uptake of iodide
medical destruction of thyroid tissue: Radioactive iodine (I131)
by inhibiting release of hormones from thyroid

Question 5

Anion inhibitors

Answer 5

for hyperthyroidism

block uptake of iodide by thyroid

Question 6

Thioamides

Answer 6

inhibit hormone synthesis (antithyroid drugs)

Propylthiouracil

Methimazole

act by inhibiting peroxidase (block iodine organification and hence coupling reactions)

Major drugs for treatment of mild thyrotoxicosis, and in preparation of patients for subtotal thyroidectomy

Question 7

Iodide salts

Answer 7

blocks hormone release

Question 8

Radioactive iodine

Answer 8

destruction of thyroid tissue

Radioactive iodine 131I emits beta particles and X-rays

131I is the only isotope used in the treatment of thyrotoxicosis while others are used in scanning
Administered as Sodium 131I orally.

Patients can become hypothyroid – managed with thyroxine (T4)

Question 9

Iodinated contrast media

Answer 9

Ipodate: inhibit peripheral conversion of T4 into T3; inhibit hormone release

Used as adjunctive therapy in the treatment of thyroid storm

Question 10

Beta blocker

Answer 10

blocks adrenergic symptoms and prevents fconversion of T4-T3

Question 11

Which thoamadie is more potent
Which is safer in pregnancy
which inhibits peripheral deiodination

Answer 11

Methimazole is more potent and longer acting (once daily dosing) than Propylthiouracil; less hepatotoxicity (Propylthiouracil associated with (fatal) hepatotoxicity) , hence preferred to propylthiouracil in adults and children

Propylthiouracil is relatively safer and preferred in first trimester of pregnancy

Propylthiouracil also inhibits peripheral deiodination (conversion) of T4 into T3 (preferred in thyroid storm).

Question 12

Thiamide use

Answer 12

(a) remission occurs in up to half of the patients of Grave’s disease after 1-2 years of pharmacotherapy;
preferred in young patients with short history of hyperthyroidism and a small goiter

(b) remissions are rare in toxic nodular goiter: surgery or 131I is preferred

Pre-Op–surgery in thyrotoxic patients is risky
young patients with florid hyperthyroidism and substantial goiters –are rendered euthyroid with antithyroid drugs before performing surgery

Question 13

Initial control with antithyroid drug ► ___ week gap ► radioiodine ► ___day gap ► resume antithyroid drugs ► _______ withdraw over 3 months as the response to ______ develops

Answer 13

Initial control with antithyroid drug ► 1-2 week gap ► radioiodine ► 5-7 day gap ► resume antithyroid drugs ► gradually withdraw over 3 months as the response to 131I develops

Question 14

Thioamides ADR

Answer 14

Common: Hypothyroidism (reversible), Nausea, Headache. Maculopapular Rash, Arthralgia, Edema,

Hepatotoxicity ****  (propylthiouracil)
Cholestatic jaundice (methimazole)

Agranulocytosis (less common, but serious)
{STOP THE DRUGS}

Question 15

Wolff-Chaikoff effect

Answer 15

In high intracellular concentration, iodide inhibits several steps in thyroid hormone biosynthesis, including iodide transport and organification (Wolff-Chaikoff effect), also inhibits hormone release

Question 16

Thyroid constipation

Answer 16

with Iodine/iodides
Thyroid status starts returning to normal with a complete stoppage of hormonal release from the gland (thyroid constipation)
Effect is reversible and transient as thyroid gland ‘escapes’ from its effect after 10-14 days

Question 17

Iodine/Iodides uses

Answer 17

1. Preoperative preparation for thyroidectomy:
   
   • generally given 7-10 days preceding thyroid surgery.
   • aim is to make the gland firm and decrease vascularity, so that easy to operate on. It is never used alone, is combined with thioamides.

Lugol’s solution (5% Iodine+ 10% Potassium iodide)

2. Thyroid storm:
   - Given IV or orally to stop any further release of T3/T4 from the thyroid

Question 18

Iodine/Iodides ADR - acute and chronic

Answer 18

Acute reactions: In sensitive individuals can cause angioedema, swelling of larynx (suffocation), swelling of lips and eyelids, rashes and hypersensitivity reactions, fever, joint pain, thrombocytopenia

Chronic overdose (Iodism): unpleasant brassy (metallic) taste, inflammation of mucous membranes, burning sensation in mouth, salivation, rhinorrhea, sneezing, headache; long term use of high doses can cause hypothyroidism and goiter.

Use in pregnancy avoided – fetal goiter.

Question 19

Radioactive iodine therapeuric effects depends on?

Answer 19

on emission of beta rays – destroy the thyroid gland (undergo pyknosis and necrosis followed by fibrosis, without damage to neighboring tissues)

Question 20

Radioactive iodine contraindicated in?

Answer 20

Pregnancy - cretinism (hypothyroid)

Question 21

The advantage of radioactive iodine vs surgery

Answer 21

NON-surgical ablation of hyperactive thyroid gland mass (Grave’s disease or toxic nodular goiter) without** damage to surrounding tissue

Question 22

Why are anion inhibitors no longer used

Answer 22

cause fatal aplastic anemia

Question 23

Thyroid storm management supportive measures

Answer 23

Supportive measures (IV fluids, antipyretics, cooling blankets, and sedation)

Propylthiouracil (preferred over methimazole** ?????)- through nasogastric tube or rectally

Iodides- orally or IV

Ipodate – ipodate inhibits hormone release and also blocks the T4 to T3 conversion

Propranolol (β-blocker)- used to control tachyarrhythmias and overall sympathetic stimulation**
Given oral 80 mg Q 4 H or IV (upto 10 mg)

Hydrocortisone (IV) – supportive therapy for possible relative adrenal insufficiency, also blocks the T4 to T3 conversion.

Question 24

Which 3 drugs inhibit the 5’-deiodinase activitity

Answer 24

β-blockers
high dose propylthiouracil and
Steroid

the 5’deiodinase is needed to convert t4->t3 so then resulting in low T3 and high rT3 concentrations.