Lecture 33: Drugs and the Thyroid

Question 1

what are the pharmacological options for treatment of hyperthyroidism

Answer 1

• block
• block and replace
• radioactive iodine
• surgery
• symptomatic control

Question 2

what class of drugs are used for the block regimen for hyperthyroidism treatment

Answer 2

thioureylenes

e. g.
- carbimazole
- propylthiouracil

Question 3

MoA of thioureylenes

Answer 3

• inhibits iodination of Tyr residues in thyroglobulin
• (inhibits thyroperoxidase?)
• 6-15 hr half life
• 90% inhibition of iodination of TG within 12 hrs
• gradual reduction in signs and symptoms of hyperthyroidism (4 weeks)

Question 4

outline some adverse effects of thioureylenes

Answer 4

common:

• rash
• pruritus
• nausea
• less hyper

rare:
- agaranulocytosis
(Px should report any signs of infection)

pregnancy: (given lowest effective dose)
- carbimazole may cause goitre/hypoT4 of foetus as it crosses placenta

Question 5

give an example of symptomatic Rx in hyperthyroidism and how it works

Answer 5

• propanolol (non-selective B blocker)
• rapid relief of thyrotoxic symptoms
• inhibits T4 to T3 conversion in peripheral tissues
• improves palpitations/arrhytmias/tremor/agitation

Question 6

explain the use of block and replace regimens

Answer 6

• less TSH so less goitre
• carbimazole + levothyroxine
• given for 18 months
• nor suitable for pregnant women

Question 7

outline the use of radioactive iodine

Answer 7

• given orally as one dose
• rapidly and selectively taken up in the thyroid
• emits short range B particle radiation damaging only thyroid follicle cells
• 8 day half life, gone in 2 months
• leads to iatrogenic hypo after 4 months
• patient will need lifelong T4 Rx

CAUTION
limit contact with infants

Question 8

what is the main drug for hypothyroid Rx

Answer 8

levothyroxine

Question 9

how is levothyroxine given to Px

Answer 9

• adjusted to symptoms and biochemistry
• introduced slowly then increased every 4 weeks esp. in elderly
• side effects only if in excess

Question 10

list some drugs that affect thyroid hormone synthesis

Answer 10

• thioureylenes
• iodides
• -> lugols iodine
• -> amiodarone
• -> iodinated contrast media
• lithium

Question 11

why might lugols iodine be used

Answer 11

• short term control of thyrotoxicosis pre op

- advantage of reducing vascularity and fragility of thyroid gland