thyroid drugs in practice

Question 1

what does the thyroid gland produce?

Answer 1

T3 and T4
T3= tri0iodothyronine
T4= thyroxine- converted to the more biologically active T3 in peripheral tissues

Question 2

what is the production of T3 and T4 essential for?

Answer 2

essential for normal growth, development and metabolism

Question 3

how are the thyroid hormones controlled?

Answer 3

negative feedback:
the hypothalamus signals to the anterior pituitary via THS
Anterior pituitary signals to thyroid for production via THS

Question 4

what are the types of thyroid disorders?

Answer 4

hypothyroidism- overt or subclinical
hyperthyroidism- overt of subclinical
goitre
thyroid cancer

Question 5

why does thyroid disfunction in pregnancy need to be well controlled?

Answer 5

as there is trimester-specific reference ranges and differing clinical priorities needed careful management

Question 6

what is usually done if a person who is pregnant is already taking levothyroxine?

Answer 6

a dose increase is usually needed

Question 7

give an example of a drug induced thyroid disorder?

Answer 7

amiodarone- class 3 arrhythmic used to treat superventricular and ventricular tachyarrhythmias

Question 8

how does amiodarone work to cause thyroid disorders?

Answer 8

hypothyroidism- block conversion of T4 to T3- compensatory increase in thyroid stimulating hormone
hyperthyroidism- due to iodine content of the drug
durg may mask clinical features of hyperthyroidism

Question 9

what monitoring should be done with amiodarone?

Answer 9

TFT monitoring before- TSH, T3,T4, thyroid antibodies
and during treatment- TSH, T3, T4
and for a year after stopping- due to a long t 1/2

Question 10

what happens if hypothyroidism occurs when taking amiodarone?

Answer 10

usually cautiously add in levothyroxine and continue amiodarone

Question 11

how can lithium cause a thyroid disorder?

Answer 11

hypothyroidism- inhibits iodine uptake and thyroid hormone release- treat with levothyroxine replacement
hyperthroidism- paradoxical effect, mechanism unknown

Question 12

what monitoring should be done with lithium?

Answer 12

TFT monitoring before and during treatment

Question 13

what should TFTs be requested?

Answer 13

• clinical suspicion of thyroid disorder dur to presenting signs/ symptoms
• to rule out as part of a screening process e.g. osteoporosis, AF, subfertility, lithium, diabetes, autoimmune diseases

Question 14

what happens in a TFT?

Answer 14

usually test TSH - and free T4
further testing - T3 and thyroid antibodies
other- biopsy, scans etc

Question 15

how do you interperte TFT readings?

Answer 15

high TSH and low T4- hypothyroidism
low TSH and high T4= hyperthyroidism
high TSH and same T4= subclinical hypothyroidism
low TSH and same T4= subclinical hyperthyroidism

Question 16

what is primary hypothyroidism?

Answer 16

primary- 95%
failure of the thyroid gland to produce thyroid hormones
-iodine def
autoimune thyroiditis
destruction of thyroid gland
drugs
congenital hypothyroidism

Question 17

what is secondary hypothyroidism?

Answer 17

aprox 5%
under production of TSH by pituitary gland
-pituitary or hypothalamic dysfunction
tumors, surgery, trauma, radiotherapy

Question 18

what is overt hypothyroidism?

Answer 18

may of may not be symptomatic

it is a decrease in T4 and an increase in TSH

Question 19

what is subclinical hypothyrodism?

Answer 19

usually asymptomatic
many people do not need treatment- interval screenings of TFTS
if symptoms- trial of levothyroxine
same T4 and inc TSH

Question 20

what are the clinical features of hypothyrodism?

Answer 20

fatigue
cold intolerance
weight gain
non-specific weakeness arthrahia
myalgia
constipation
menstrual irregularities
depression
impaired concentration and memory
dry skin and reduced body and scalp hair
thyroid pain

Question 21

what are the signs of hypothyroidism?

Answer 21

changes to appearance- coarse dry hair and skin and hair loss
oedema
vocal changes- hoarsness or deepening of the voice
goitre
bradycardia
diastolic hpt
delayed releaction of deep tendon reflexes
paraesthesia

Question 22

what are the complications of hypothyroidism?

Answer 22

CV complications- dyslipidaemia, CHD, HF
reproductive- fertility, complications in pregnancy
neurological- deafness, concentration, memory, language perception
myxoedema coma- medical emergency

Question 23

how do you manage overt hypothyrodism?

Answer 23

often managed in primary care
1st line- levothyroxine - aim to resolve signs/ symptoms, normalise TSH
liothyronine- rarely used- endocrinologist

Question 24

what dose of levothroxine should be given?

Answer 24

dose is adjusted based on clinical signs and symptoms of a biochemical response
1.6 mcg/kg/day- rounded to nearest 25 mcg for adults< 65
-higher starting dose- more rapid improvememys than lower followed by titration
inc 25-50 mcg increments every 3-4 weeks
usual maintenance 100-200 mcg increments every 3-4 weeks

Question 25

when would you give a lower starting dose of levothyroxine?

Answer 25

if ischaemic heart disease or >60-65 years | 25-50mcg adjusted in 25 mcg increments

Question 26

what should you monitor for levothyroxine?

Answer 26

TSH and patients symptoms; adjust/ titrate dose | TFTs at least 3 montly until stable TSH reached then annually

Question 27

what are the s/e of levothyroxine- usually associated with excess dosing?

Answer 27

``` GI disturbances CV arrhythmias, tachycardia flushing, fever, heat intolerence weight loss hypersensitivity rxn- rash, oedema muscle cramps, weakness anxiety, tremor, restlessness, insomnia mania menstrual irregularities headache ```

Question 28

what does levothyroxine interact with?

Answer 28

calcium/ antacids/ iron salts | therefore take 4 hours apart

Question 29

when should levothyroxine be taken?

Answer 29

ideally should be taken at least 30 min before brekfast, caffine containing liquids or other drugs

Question 30

what is hyperthyroidsim?

Answer 30

excess of circulating thyroid hormones :dec TSH and inc T4

Question 31

what is primary hyperthyroidism?

Answer 31

most commonly is graves disease- autoimmune -antibodies stimulate and increase secretion of thyroid hormones confirmed by testing for TSH receptor antibodies- secondary care other causes- toxic multinodular goitre, toxic thyroid nodule, drugs eg- amiodarone/ lithium

Question 32

what causes secondary HYperthyroidism?

Answer 32

TSH secreting pituitary tumour

Question 33

what are some of the complications of hyperthyroidism?

Answer 33

cardiovascular- including arterial fibrillation and associated increased stroke risk osteoproosis eye disease- vision loss thyroid storm- release of large am of thyroid hormone- worsening of symptoms

Question 34

what are some of the clinical symptoms of hyperthyroidism?

Answer 34

Breathlessness, dysphagia, neck pressure (may be caused by a toxic multinodular goitre).Hyperactivity Emotional lability Insomnia, irritability, anxiety Palpitations Exercise intolerance Fatigue, muscle weakness Heat intolerance Increased appetite with weight loss Diarrhoea Infertility, oligomenorrhoea, amenorrhoea. Polyuria Generalized itch Reduced libido, gynaecomastia in men. Deterioration in blood glucose control and hyperglycaemia in people with diabetes mellitus

Question 35

what are some of the signs of hyperthyroidism?

Answer 35

Agitation, fine tremor, warm moist skin, palmar erythema. Sinus tachycardia, atrial fibrillation, heart failure, dependent oedema. Eye signs. Goitre Gynaecomastia in men Splenomegaly Muscle wasting

Question 36

how do you manage hyperthyroidism?

Answer 36

* Refer to specialist and consider following options: * Surgery * Radioiodine treatment * Antithyroid drugs – carbimazole, propylthiouracil–Short-term while waiting for specialist review–Short-term in prep for radioiodine treatment or surgery–Medium-term in inducing remission of Grave’s disease–Long-term where radioiodine treatment or surgery is contraindicated or declined * Consider prescribing a beta-blocker and titrating the dose depending on clinical response, to provide relief of adrenergic symptoms

Question 37

what is radioiodine treatment?

Answer 37

* Induces damage of DNA leading to death of thyroid cells. | * Radioprotection measures after treatmen

Question 38

who is radioiodine treatment not recommended for?

Answer 38

Not recommended for people with active thyroid eye disease as it may worsen this •Contraindicated in pregnancy and in women who are breastfeeding.–Women should be advised to avoid becoming pregnant for at least six months after radioiodine treatment.–Men should be advised not to father children for at least four months after radioiodine treatment.

Question 39

what happens to people with graves disease?

Answer 39

they become euthyroid and then hypothyrodi within 6 weeks to 6 months after completing radioiodine treatment

Question 40

what are some anti-thyroid drugs? how do they work?

Answer 40

carbimazole and propylthyiouracil •Decrease thyroid hormone synthesis, by acting as a preferred substrate for iodination by thyroid peroxidase, the key enzyme in thyroid hormone synthesis. •Check FBC and LFT first. carbimazole perfered

Question 41

what risk does propylthiouracil pose?

Answer 41

Propylthiouracil has a small risk of severe liver injury (about 1 in 10,000)

Question 42

what happens to people with graves disease who who have been taking carbimazole?

Answer 42

they can become euthroid after 4-8 weeks of treatment

Question 43

how is the length of treatment adjusted with people with severe hyperthroidism , a large goitre or recent exposure to iodide?

Answer 43

may need a longer duration of treatment

Question 44

how are anti-thyroid drugs given?

Answer 44

high dose usually carbmizole is given initially, the following repeat TFT, if things are improving, adjustment of medication by either: -titration block regime- 40% -dose adj every 4-6 week/ if T4 falls too low or low-normal levels indicating hypothyroidism block and replace regime-60%- the anti-thyroid drug is used to block the synthesis of thyroid hormone. T4 is monitored and levtthyroxine is added. adjustment to levothyroxine to maintain T4 levels in the range remission rate about 50% if treatment is continued for 6-18 months and then stopped

Question 45

what are the adverse effects of carbimazole?

Answer 45

nausea/ taste disturbances/ headache/ fever/ malaise/ arthralgia itch and rahs- can usually be treated with antihistamines without the need to stop drug treatment bone marrow suppression hepatobiliary disorders

Question 46

how should carbimazole be given?

Answer 46

15-40mg daily reduced to maintenance dose of 5-15mg usually for 12-18 months or if using as part of a block and replace regime 40-60mg daily

Question 47

what are the signs and symptoms of bone marrow suppression with carbimazole?

Answer 47

infection especially sore throat and fever wbc count perferomed and drug stopped

Question 48

what are the s/e of propylthiouracil?

Answer 48

leucopenia hepatic disorders •Rarely, cutaneous vasculitis, thrombocytopenia, pancytopenia, aplastic anaemia, agranulocytosis, hypoprothrombinaemia, nephritis, lupus erythematous-like syndromes.

Question 49

what dose of propylthiouracil should be given?

Answer 49

* 200 to 400mg daily in divided doses in adults * Maintained until the patient becomes euthyroid; the dose may then be gradually reduced to a maintenance dose of 50 to 150mg daily in divided doses. * Dose adjustments in renal impairment