Hypothyroidism & Disorders

Question 1

Common causation of primary hypothyroidism?

Answer 1

Autoimmune damage to the thyroid gland

Question 2

Common presentation on primary hypothyroidism inside the body?

Answer 2

Thyroxine (T4) = LOW levels

TSH = HIGH levels

Question 3

Symptoms of primary hypothyroidism?

Answer 3

EVERYTHING SLOWS DOWN!

x Deepening voice
x Bradycardia
x Cold intolerance
x Weight gain
x Reduced appetite
x Constipation
x Depression & tiredness
x Eventual myxoedema coma

Question 4

Which is more active, T4 (thyroxine) or T3 (tri-iodothyronine)

Answer 4

T3!

T4 (pro-hormone) is converted to T3 via. deiodinase enzyme

Question 5

How does T3 carry out its affects?

Answer 5

1. T3/4 enter the nucelus (T4 converted to T3)
2. T3 binds to a hetrodimer of RXR & TR (ONENOTE!!)
3. Binds to a part of a DNA called the TRE (thyroid response element) = effects

Question 6

Main treatment for hypothyroidism?

Answer 6

Thyroid Hormone Replacement Therapy

Question 7

2 types of Thyroid HRT?

Answer 7

T4 (levothyroxine sodium)
OR
T3 (liothyonine sodium)

Question 8

In which scenarios is levothyroxine sodium normally used?

Answer 8

1. Autoimmune primary hypothyroidism
2. Iatrogenic Primary hypothyroidism
3. Secondary hypothyroidism

Question 9

How is levothyroxine given in autoimmune/iatrogenic primary hypothyroidism?

Answer 9

Oral

Question 10

How is levothyroxine given in autoimmune/iatrogenic secondary hypothyroidism?

Answer 10

Oral

Question 11

How is the levothyroxine sodium dose determined in secondary hypothyroidism?

Answer 11

TSH is low due to anterior P.G failure - so CANNOT use TSH as a guide

Therefore, aim to move fT4 (free T4) to the middle of the reference range

Question 12

How is the levothyroxine sodium dose determined in primary hypothyroidism?

Answer 12

TSH used as a guidance for thyroxine dosage - aim is to suppress TSH into the reference range

(so given until TSH levels falls) - point at which it happens is the set dosage point for the patient)

Question 13

In which scenarios is liothyronine sodium normally used?

Answer 13

Myxoedema coma - given when want rapid affect!

Question 14

How is liothyronine sodium normally given?

Answer 14

Intravenously - as onset of action faster than T4 & oral

Question 15

How does Combined Thyroid HRT work?

Answer 15

Combination of T4/T3 given (supressess TSH)

Question 16

What is an issue with Combined Thyroid HRT?

Answer 16

T3 is so potent that can offten get effects of excess hormones - ‘toxicity’

Includes, palpitations, termor, anxiety (due to low TSH)

Question 17

Pharmokinetics of the 2 drug types?

Answer 17

1. Active orally
2. Long half-life
   - Levothyroxine - 6 days
   - Liothyonine - 2.5 days
3. 99.97% of levothyroxine and 99.7% of liothyonine are PPB (mainly to TBG)

Question 18

When does PPB increase?

Answer 18

x pregnancy

x on prolonged treatment with oestrogens and phenothiazines

Question 19

When does TBG levels fall?

Answer 19

x malnutrition

x liver disease

Question 20

When can their be competition with PPB?

Answer 20

With certain co-administered drugs e.g. phenytoin