hypothyroidism

Question 1

how is hypothyroidism treated

Answer 1

Levothyroxine: synthetic form of T4
Peripherally converted to T3

Liothyronine: synthetic form of T3

Question 2

what drugs reduce levothyroxine absorption

Answer 2

PPIs, calcium salts, ferrous sulfate, and bile acid sequestrants.

Question 3

what is the most common cause of hypothyroidism

Answer 3

Hashimoto thyroiditis

Question 4

how do you diagnose hypothyroidism

Answer 4

obtain TSH level

Question 5

what drugs cause hypothyroidism

Answer 5

radioactive iodine, amiodarone, lithium, carbimazole, propythioruacil

Question 6

how does radioactive iodine cause hypothyroidism

Answer 6

breaks down thyroid tissue
and induces a hypothyroid state, which can then be treated with levothyroxine.

Question 7

how does amiodarone cause hypothyroidism

Answer 7

Amiodarone is an anti-arrhythmia drug which is rich in iodine and can induce thyroid gland
dysfunction.

Question 8

what tests need to be taken before commencing amiodarone

Answer 8

thyroid
function test 3 to 4 months before taking amiodarone.

Question 9

how does lithium cause hypothyroidism

Answer 9

Lithium inhibits the synthesis of both T3 and T4 as well as also inhibiting the release of T3
and T4 from the thyroid gland.

Question 10

what tests should be taken on lithium

Answer 10

when a patient is
starting lithium therapy a TFT (thyroid function test) should take place and they should have
a TFT every 6 to 12 months

Question 11

what can carbimazole cause?

Answer 11

immunosuppressant effect which underlies their most dangerous ADR
which is bone marrow suppression (although this ADR is rare), given the potential
seriousness of this ADR it is important to warn the patient to report any sudden or severe
sore throat associated with fever which is a common sign of bone marrow suppression

Question 12

how do you diagnose hypothyroidism

Answer 12

TSH in the blood
Free T3 in the blood
Free T4 in the blood

Question 13

why do we measure only free levels of t3 and t4

Answer 13

two types of thyroid hormone
circulating our body, the ones that are bound to proteins in our body and the free flowing thyroid
hormone that is present and the free hormone which is the hormone which has a pharmacological
response

Question 14

what is the most important thyroid function test

Answer 14

The most important test is the TSH test as it is more sensitive than T3 and T4, because there is no
protein bound reservoir of TSH as opposed to T3 and T4.

Question 15

how is hypothyroidism treated?

Answer 15

Levothyroxine (T4) or liothyronine(T3)
Liothyronine = rapid onset of action, metabolised quickly, used for acute hypothyroid states.

Question 16

what are the adr for levothyroxine

Answer 16

• Diarrhea (increase basal metabolic rate and the transit time of your GI, lower dose to
  overcome this)
• Angina, palpitations and tachycardia (because thyroid hormones will increase heart rate )
• Weight loss (basal metabolic rate increases so you’re going to burn more fat)

Question 17

what are the drug interactions between ferrous sulphate and levothyroxine

Answer 17

FS will affect the absorption of T4 from the GIT leading to a decrease in the amount of T4 absorbed,
and therefore a reduced level of T4 in the blood. Lower levels of T4 means the body will increase
more TSH to counteract the low levels of T4. To overcome this we have to keep at least a 2 hour gap
between ferrous sulphate and levothyroxine.

Question 18

what is the interaction between phenytoin and levothyroxine

Answer 18

Phenytoin is an enzyme inducer causing the rate at which T4 is metabolised in the liver to be
increased leading to a lower level of T4 present in the blood. This can be worked around by simply
increasing the amount of levothyroxine present in the blood.

Question 19

what is the interaction between levothyroxine and warfarin

Answer 19

Levothyroxine will enhance the anticoagulant effects of warfarin as LT will increase the metabolism of
clotting factors which means there is less clotting going on increasing the risk of bleeding. monitor INR

Question 20

how is levothyroxine prescribed

Answer 20

• take it in the morning
  Want to avoid taking levothyroxine with food, so take it ONE hour before food so it is given time to
  be absorbed.

IF taken alongside food then it will result in erratic absorption of levothyroxine and
unstable blood levels of thyroid hormone

Question 21

how long does it take levothyroxine to start working

Answer 21

it takes a few weeks to work, as most symptoms will take time to work. Levothyroxine is extensively
protein bound s