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PHA 332 > thyroid drugs in practice > Flashcards

thyroid drugs in practice Flashcards

1
Q

what does the thyroid gland produce?

A

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

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2
Q

what is the production of T3 and T4 essential for?

A

essential for normal growth, development and metabolism

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3
Q

how are the thyroid hormones controlled?

A

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

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4
Q

what are the types of thyroid disorders?

A

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

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5
Q

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

A

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

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6
Q

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

A

a dose increase is usually needed

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7
Q

give an example of a drug induced thyroid disorder?

A

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

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8
Q

how does amiodarone work to cause thyroid disorders?

A

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

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9
Q

what monitoring should be done with amiodarone?

A

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

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10
Q

what happens if hypothyroidism occurs when taking amiodarone?

A

usually cautiously add in levothyroxine and continue amiodarone

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11
Q

how can lithium cause a thyroid disorder?

A

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

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12
Q

what monitoring should be done with lithium?

A

TFT monitoring before and during treatment

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13
Q

what should TFTs be requested?

A
  • 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
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14
Q

what happens in a TFT?

A

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

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15
Q

how do you interperte TFT readings?

A

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

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16
Q

what is primary hypothyroidism?

A 
primary- 95%
failure of the thyroid gland to produce thyroid hormones
-iodine def
autoimune thyroiditis
destruction of thyroid gland
drugs
congenital hypothyroidism
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17
Q

what is secondary hypothyroidism?

A

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

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18
Q

what is overt hypothyroidism?

A

may of may not be symptomatic

it is a decrease in T4 and an increase in TSH

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19
Q

what is subclinical hypothyrodism?

A

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

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20
Q

what are the clinical features of hypothyrodism?

A 
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
21
Q

what are the signs of hypothyroidism?

A

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

22
Q

what are the complications of hypothyroidism?

A

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

23
Q

how do you manage overt hypothyrodism?

A

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

24
Q

what dose of levothroxine should be given?

A

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

25
Q

when would you give a lower starting dose of levothyroxine?

A

if ischaemic heart disease or >60-65 years

25-50mcg adjusted in 25 mcg increments

26
Q

what should you monitor for levothyroxine?

A

TSH and patients symptoms; adjust/ titrate dose

TFTs at least 3 montly until stable TSH reached then annually

27
Q

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

A 
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
28
Q

what does levothyroxine interact with?

A

calcium/ antacids/ iron salts

therefore take 4 hours apart

29
Q

when should levothyroxine be taken?

A

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

30
Q

what is hyperthyroidsim?

A

excess of circulating thyroid hormones :dec TSH and inc T4

31
Q

what is primary hyperthyroidism?

A

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

32
Q

what causes secondary HYperthyroidism?

A

TSH secreting pituitary tumour

33
Q

what are some of the complications of hyperthyroidism?

A

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

34
Q

what are some of the clinical symptoms of hyperthyroidism?

A

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

35
Q

what are some of the signs of hyperthyroidism?

A

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

36
Q

how do you manage hyperthyroidism?

A
  • 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
37
Q

what is radioiodine treatment?

A
  • Induces damage of DNA leading to death of thyroid cells.

* Radioprotection measures after treatmen

38
Q

who is radioiodine treatment not recommended for?

A

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.

39
Q

what happens to people with graves disease?

A

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

40
Q

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

A

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

41
Q

what risk does propylthiouracil pose?

A

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

42
Q

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

A

they can become euthroid after 4-8 weeks of treatment

43
Q

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

A

may need a longer duration of treatment

44
Q

how are anti-thyroid drugs given?

A

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

45
Q

what are the adverse effects of carbimazole?

A

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

46
Q

how should carbimazole be given?

A

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

47
Q

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

A

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

48
Q

what are the s/e of propylthiouracil?

A

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

49
Q

what dose of propylthiouracil should be given?

A
  • 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

PHA 332 (42 decks)

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