hypothyroidism Flashcards
how is hypothyroidism treated
Levothyroxine: synthetic form of T4
Peripherally converted to T3
Liothyronine: synthetic form of T3
what drugs reduce levothyroxine absorption
PPIs, calcium salts, ferrous sulfate, and bile acid sequestrants.
what is the most common cause of hypothyroidism
Hashimoto thyroiditis
how do you diagnose hypothyroidism
obtain TSH level
what drugs cause hypothyroidism
radioactive iodine, amiodarone, lithium, carbimazole, propythioruacil
how does radioactive iodine cause hypothyroidism
breaks down thyroid tissue
and induces a hypothyroid state, which can then be treated with levothyroxine.
how does amiodarone cause hypothyroidism
Amiodarone is an anti-arrhythmia drug which is rich in iodine and can induce thyroid gland
dysfunction.
what tests need to be taken before commencing amiodarone
thyroid
function test 3 to 4 months before taking amiodarone.
how does lithium cause hypothyroidism
Lithium inhibits the synthesis of both T3 and T4 as well as also inhibiting the release of T3
and T4 from the thyroid gland.
what tests should be taken on lithium
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
what can carbimazole cause?
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
how do you diagnose hypothyroidism
TSH in the blood
Free T3 in the blood
Free T4 in the blood
why do we measure only free levels of t3 and t4
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
what is the most important thyroid function test
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.
how is hypothyroidism treated?
Levothyroxine (T4) or liothyronine(T3)
Liothyronine = rapid onset of action, metabolised quickly, used for acute hypothyroid states.
what are the adr for levothyroxine
- 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)
what are the drug interactions between ferrous sulphate and levothyroxine
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.
what is the interaction between phenytoin and levothyroxine
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.
what is the interaction between levothyroxine and warfarin
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
how is levothyroxine prescribed
- 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
how long does it take levothyroxine to start working
it takes a few weeks to work, as most symptoms will take time to work. Levothyroxine is extensively
protein bound s
