Pharmacology of Thyroid Hormone Flashcards
Iodide uptake from circulation occurs via
Sodium-Iodide symporter
Iodide is extruded from the thyroid follicle by…
Pendrin
Oxidation of iodide is catalyzed by…
Thyroid Peroxidase
Coupling of mono and di-iodotyrosyl residues is catalyzed by…
Thyroid Peroxidase
T4–>T3 peripheral conversion is mediated by…
Types I II and III 5’ deiodinases
Some drugs that decrease binding of thyroxine to TBG
Glucocorticoids Androgens Salicylates Anti-seizure meds (phenytoin, carbamazeine) Furosemide
Effect of severe myxedema on thyroid absorption
Severely hampered
Administer via IV
Important of Thyroid binding proteins. When are they high? Low?
They have a major effect on the rate of the degradation of thyroid hormone.
High – Pregnancy
Low – Nephrosis, Cirrhosis
Thyroid hormone is excreted as
bile –> stool
Important thyroid preparations
Levothyroxine Sodium (synthetic T4) Liothyronine Sodium (T3) Liotrix (Mix of the above two, 4:1 respectively)
Effects of soy/bran/coffee on thyroid hormone absorption
Attenuate it, take 30-60 minutes before meals
Why would you use Liothyronine Sodium instead of levothyroxine
Recent hypothyroidism, overtreatment with anti-thyroid drugs
After radioiodide treatment, post htyroidectomy
Details of treatmnet of simple goiter
Replacement therapy to drop TSH levels and decrease size of the goiter.
In thyroid patients contraindicated for betablockers (asthma) treat with….to control tachycardia
Diltiazem
______ disease may be associated with nodular thyroid tumors
Plummer’s
Six categories of major anti-thyroid drugs
- Blockers of Thyroid Hormone synthesis
- Ionic inhibitors that block iodide transport
- Iodide (blocks thyroid hor. synthesis at high conc)
- Iodinated Contrast (blocks T3-4 conversion and synth)
- Radioactive Iodine (destroys gland with ionizing radiation
- Lithium (suppresses synthesis and release)
Drugs that block thyroid hormone synthesis
1, Thioamides (Methimazole, PTU, Carbimazole)
- Aniline Derivatives (Sulfathiazole)
- Polyhydric Phenols (Resorcinol)
How do thioamides work?
Block Thyroid Peroxidase
(no oxidation, organification)
PTU also blocks peripheral T3–>T4
Important details about thioamide absorptiona dn degradation
PTU bioabailability is 50-80%. survives first liver pass.
Methimazole is completely absorbed, but slowly.
Both accumulate in thyroid and are excreted mostly in glucuronidated conjugates in urine.
Difference between Methimazole and PTU
Meth. is about 10x as potent
PTU is for people who can’t meth and preggers
Important bad side effect from thioamide treatment
Agranulocytosis
PTU - Hep
Meth – Jaundice
What is the Wolf-Chaikoff effect
Iodide inhibits the synthesis of iodotyrosine and iodothhyronine
Most important clinical effect of iodide
Inhibits the release of thyroid hormone
Common adverse effects of iodide
Rash, Swollen Salivary Glands, Metallic Taste, COnjunctivitis
