Thyroid

Question 1

T3 vs T4

Answer 1

NON PEPTIDE HORMONES(THReceptor=Nuclear Transcription Factor)

T4 more prevalent

T4 more bound in plasma

T4 has longer halflife

T3 is 5-10x more potent!

HOLDS TRUE FOR DRUG FORMS TOO

BOTH HORMONES TARGET NEARLY ALL TISSUES

LONGTERM EFFECTS

Question 2

Liothyronine

Answer 2

• Pure T3
• Rapid Onset, Short Duration
• 4x more potent than Levo
• Rarely used in chronic therapy
• Used some presurgery or while waiting for Levo to take effect
  *

Question 3

Levothyroxine

Answer 3

• Pure T4
• Slow Onset, Long Duration
• Converted to T3
• Typical Dose=100ug per day
• Less potent than Liothyonine, More protein bound, Longer half life
• Converted to T3 peripherally
• Primary Drug Used b/c Long Duration, more predictable effects
  
  • ​USED EVEN IN MYXEDEMA COMA
• Side effects- due to Over Use

Drug Interactions are very common, stress can all alter TH action

• USED FOR SUPPRESSIVE THERAPY IN SOME THYROID CANCER

​

Question 4

Thyroid Hormone Therapeutic Considerations

Answer 4

Slow Onset, Days-Weeks

Long Duration of Effects(Slow reversibility)

For Old pts- Give small doses initially and gradually increase while observing Cardiac Function

**Continue to Use during Pregnancy–>health of mother, fetus **

-TH needs will increase throughout pregnancy

-Myxedema coma=Levothyroxine IV BOLUS

Question 5

Propanolol

Answer 5

• Beta Blocker
• Provides Symptomatic relief of HYPERthyroidism

Question 6

Methimazole

Answer 6

• THIOAMIDE
• Used to inhibit synthesis or release of TH
• First line Therapy for NON DESTRUCTIVE–> Effects take a while to be seen b/c long duration of Methimazole
• More Potent than PTU, Has longer Half life (VERY IMPORTANT
• no liver toxicity like PTU
• Doesnt affect peripheral conversion like PTU does
• DOES HAVE FETAL TOXICITY not seen in PTU

Question 7

Propylthiouracil

Answer 7

• THIOAMIDE
• Rapid control of TH production
• **Short Half Life **
• Therapy last 1 year
• Prefered therapy during PREGNANCY
• Adverse Effect:PTU and Methimazole cause agranulocytosis
  
  • ​first few months of therapy
  • Sore throat/fever
  • Use Abs to treat infection
• Other Adverse: skin rash, Drug fever, arthralgia, myalgia, Can cause Hypothyroidism which is reversible

Question 8

Potassium Iodide

Answer 8

• Decrease Size and vascularity of Thyroid gland
• Mech: Block synthesis and RELEASE of TH
  
  • Doesnt effect peripheral conversion
• Rapid effects but Short Duration
• Use: Pre-op 10 days before thyroidectomy, Also used during Thyroid Storm to prevent release of more TH
• Used to block Iodine uptake during radioactive exposure crisis
• Adverse=Sore throat, Rash, Diarrhea

Question 9

Radioactive Iodine

Answer 9

I131 is isotope

• Used for local destruction, 1-2 mm penetration
• USE THIOAMIDES prior to scheduled radio-iodine
• Easy, effective, cheap, painless with localized effect
• Transient or Permanent Hypothyroidism

-DEFINITIVE THERAPY-safer than surgery

-Use surg when cancer is present,

Question 10

Thyroidectomy Drug Regiment

Answer 10

1. Thioamides(Methimazole/PTU) 5-6 wks
2. Potassium Iodides- 2 weeks before -decrease size and blood flow
3. Levothyroxine after surg- for potential hypothyroidism
   4.

Question 11

Choice of Treatment for Hyperthyroidism

1. Young
2. Old
3. Pregnant
   4.

Answer 11

1. Methamizole
2. Radioactive Iodine
3. **PTU or Surg, avoid radioactive **

Question 12

Thyroid Storm

Answer 12

1. PTU- decrease T4-T3 conversion
2. Iodides- decrease TH release
3. Glucocorticoids-prevent shock
4. Propanolol- decrease symptathetic effects
   5.