Hypothyroidism & Disorders Flashcards
Common causation of primary hypothyroidism?
Autoimmune damage to the thyroid gland
Common presentation on primary hypothyroidism inside the body?
Thyroxine (T4) = LOW levels
TSH = HIGH levels
Symptoms of primary hypothyroidism?
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
Which is more active, T4 (thyroxine) or T3 (tri-iodothyronine)
T3!
T4 (pro-hormone) is converted to T3 via. deiodinase enzyme
How does T3 carry out its affects?
- T3/4 enter the nucelus (T4 converted to T3)
- T3 binds to a hetrodimer of RXR & TR (ONENOTE!!)
- Binds to a part of a DNA called the TRE (thyroid response element) = effects
Main treatment for hypothyroidism?
Thyroid Hormone Replacement Therapy
2 types of Thyroid HRT?
T4 (levothyroxine sodium)
OR
T3 (liothyonine sodium)
In which scenarios is levothyroxine sodium normally used?
- Autoimmune primary hypothyroidism
- Iatrogenic Primary hypothyroidism
- Secondary hypothyroidism
How is levothyroxine given in autoimmune/iatrogenic primary hypothyroidism?
Oral
How is levothyroxine given in autoimmune/iatrogenic secondary hypothyroidism?
Oral
How is the levothyroxine sodium dose determined in secondary hypothyroidism?
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
How is the levothyroxine sodium dose determined in primary hypothyroidism?
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)
In which scenarios is liothyronine sodium normally used?
Myxoedema coma - given when want rapid affect!
How is liothyronine sodium normally given?
Intravenously - as onset of action faster than T4 & oral
How does Combined Thyroid HRT work?
Combination of T4/T3 given (supressess TSH)
What is an issue with Combined Thyroid HRT?
T3 is so potent that can offten get effects of excess hormones - ‘toxicity’
Includes, palpitations, termor, anxiety (due to low TSH)
Pharmokinetics of the 2 drug types?
- Active orally
- Long half-life
- Levothyroxine - 6 days
- Liothyonine - 2.5 days - 99.97% of levothyroxine and 99.7% of liothyonine are PPB (mainly to TBG)
When does PPB increase?
x pregnancy
x on prolonged treatment with oestrogens and phenothiazines
When does TBG levels fall?
x malnutrition
x liver disease
When can their be competition with PPB?
With certain co-administered drugs e.g. phenytoin
