Thyroid Drugs Flashcards
The peroxidase enzyme mediates what process? Where does this process occur?
Mediates the incorporation of iodide into thyrosine residues of the thyroglobulin (TG) protein. The peroxidase then mediates the coupling of iodinated thyrosines to form T3 and T4.
Thyroid gland
Where are T3 and T4 stored?
Thyroid follicle cells
What process must occur before T3 and T4 can be released into the blood?
Proteolysis of the thyroglobulin molecule
Which thyroid hormone is the active hormone which is the inactive?
T3- active
T4- inactive
What are the Drugs used in Hypothyroidism?
L-thyroxine (T4)
Triiodothyronine (T3)
Which drug is the preferred drug in Hypothyroidism and why?
T4 is preferred over T3 due to its longer half-life, affordability, easier to monitor and does not have the immediate cardiovascular effects that T3 does.
How is T3 given?
IV
What can the physiologic doses of the drugs for hypothyroidism mimic? What are these symptoms?
Hyperthyroidism
CA effects, weight loss, osteoporosis
What is the most common form of hyperthyroidism?
Graves Disease
What is the rationale behind treating hyperthyroidism?
To destroy hyperactive cells or directly inhibit thyroid hormone synthesis or release
Which disease is more difficult to treat, Hyperthyroidism or Hypothyroidism?
Hyperthyroidism
What are the drugs used to treat hyperthyroidism?
Thioamide drugs (Methimazole and Propylthiouracil(PTU)) Radioactive iodine (131 I) Potassium Iodide (KI) Propanolol Iodinated Radiocontrast Media (Ipodate)
What are the thioamide drugs? Where do they target?
Methimazole and Propylthiouracil (PTU)
They both directly inhibit the peroxidase enzyme (Step 2) in T4 and T3 biosynthesis. PTU also inhibits deiodination of T4 to T3 in the liver (Step 4)
What does PTU inhibition of the deiodinization of T4 to T3 do?
Blood levels of T3 decline more rapidly than T4
When administering a thioamide drug how long should you expect the onset to be?
They are slow onset drugs, 2-4 weeks to become euthyroid, due to continued release of preformed T4 and T3
What is the toxicity of the thioamide drugs?
Both drugs are well tolerated; skin rash is sometimes seen
What is significant about using these drugs with Graves Disease?
High relapse rate due to continued auto-antibody presence/production
What is the mechanism of Radioactive Iodine?
Active uptake exclusively into the thyroid follicle cells; localized tissue destruction
Why is radioactive iodine considered a safe drug?
It specifically targets thyroid follicle cells which are essentially the only storage and receptor sites for iodine in the body. If there were more cells that took up iodine than the radioactive form would destroy those cells too.
What are the contraindications of radioactive iodine?
Children, older patients and pregnant women (it can cross the placenta and kill the fetus)
What are the complications of radioactive iodine?
Transient hyperthyroidism
permanent hypothyroidism
Why is the permanent hypothyroidism complication preferred to hyperthyroidism?
It is easier to maintain and can be given T4 and monitored on this drug for life
What is the mechanism of Potassium Iodide?
The “paradoxical” inhibition of iodine uptake (step 1), the peroxidase enzyme (step 2) and the proteolytic release of T3 and T4 (Step 3)
Essentially it inhibits all the processes within the thyroid gland itself
KI is the only agent to inhibit which process?
The proteolytic release of T3 and T4
What is onset and duration of KI?
Short term drug with only a week long effect
Which drug is KI usually used in combination with in the treatment of Hyperthyroidism? Why?
KI and a Thioamide Drug are usually used in combination because of their onsets. KI can act quickly with a fast onset and when its effect wares off the Thioamides effect will be just getting started since it has a slow onset.
When would you use propranolol in the treatment of hyperthyroidism?
It is used as a SYMPTOMATIC CONTROL of B-adrenergic action. It also inhibits the deionization of T4 to T3 in the peripheral tissues at high doses.
What does Ipodate do?
Inhibits T4 deiodinization (Step 4) therefore rapidly decreasing T3 concentrations.
When is Ipodate used?
Only if no response to other drugs
T/F: Some drugs can alter the binding of T4 to thyroxine-binding globulin (TBG)
True; these drugs or hormones can mimic hyper- and hypothyroidism
Draw out the thyroid gland and the process of synthesizing T3 from iodine. Also write out where each of the drugs discussed has its mechanism of action.
Do not just click to see this actually draw it out lazy
