Thyroid Flashcards
What is the treatment of choice for replacement therapy in hypothyroid patients
Levothyroxine (T4)
Long half life (7 days) and permits once daily to weekly administration
What is a synthetic slat of T3
Liothyronine (T3) has shorter half life (24 H) requiring multiple daily doses, may have greater risk of cardiotoxicity** and more difficult to monitor
Therapeutic uses of TH
- Cretinism
- Adult hypothyoidism
- Myxedema coma
- Nontoxic goiter
What are the Rx pharmacologic measures
by inhibiting synthesis
by inhibiting uptake of iodide
medical destruction of thyroid tissue: Radioactive iodine (I131)
by inhibiting release of hormones from thyroid
Anion inhibitors
for hyperthyroidism
block uptake of iodide by thyroid
Thioamides
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
Iodide salts
blocks hormone release
Radioactive iodine
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)
Iodinated contrast media
Ipodate: inhibit peripheral conversion of T4 into T3; inhibit hormone release
Used as adjunctive therapy in the treatment of thyroid storm
Beta blocker
blocks adrenergic symptoms and prevents fconversion of T4-T3
Which thoamadie is more potent
Which is safer in pregnancy
which inhibits peripheral deiodination
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).
Thiamide use
(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
Initial control with antithyroid drug ► ___ week gap ► radioiodine ► ___day gap ► resume antithyroid drugs ► _______ withdraw over 3 months as the response to ______ develops
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
Thioamides ADR
Common: Hypothyroidism (reversible), Nausea, Headache. Maculopapular Rash, Arthralgia, Edema,
Hepatotoxicity **** (propylthiouracil) Cholestatic jaundice (methimazole)
Agranulocytosis (less common, but serious)
{STOP THE DRUGS}
Wolff-Chaikoff effect
In high intracellular concentration, iodide inhibits several steps in thyroid hormone biosynthesis, including iodide transport and organification (Wolff-Chaikoff effect), also inhibits hormone release
Thyroid constipation
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
Iodine/Iodides uses
- 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)
- Thyroid storm:
- Given IV or orally to stop any further release of T3/T4 from the thyroid
Iodine/Iodides ADR - acute and chronic
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.
Radioactive iodine therapeuric effects depends on?
on emission of beta rays – destroy the thyroid gland (undergo pyknosis and necrosis followed by fibrosis, without damage to neighboring tissues)
Radioactive iodine contraindicated in?
Pregnancy - cretinism (hypothyroid)
The advantage of radioactive iodine vs surgery
NON-surgical ablation of hyperactive thyroid gland mass (Grave’s disease or toxic nodular goiter) without** damage to surrounding tissue
Why are anion inhibitors no longer used
cause fatal aplastic anemia
Thyroid storm management supportive measures
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.
Which 3 drugs inhibit the 5’-deiodinase activitity
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.
