Hypothyroidism

Question 1

Clinical use of Levothyroxine sodium (synthetic thyroxine)

Answer 1

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Question 2

Levothyroxine sodium for primary hypothyroidism

Answer 2

• used clinically for primary hypothyroidism (eg: autoimmune, iatrogenic post-thyroidectomy, post-radioactive iodine)
• oral administration
• use TSH as guidance for dose fo thyroxine (aim to suppress TSH into reference range)

Question 3

Levothyroxine sodium for secondary hypothyroidism

Answer 3

• oral administration
• used clinically for secondary hypothyroidism (eg: pituitary tumour, post-pituitary surgery or radiotherapy)
• low TSH due to anterior pituitary failure, so TSH not used as guide to dose
• aim for free T4 to be in middle of reference range

Question 4

Clinical use of Liothyronine (synthetic trio-iodothyronine)

Answer 4

• used clinically for myxoedema coma (very rare complication of hypothyroidism)
• initially intravenous administration as onset of action faster than T4
• oral administration when possible after intravenous administration

Question 5

Combined thyroid hormone replacement

Answer 5

• T4 and T3
• Some reported well-being improvement when using combination treatment
• Complicated by symptoms of ‘toxicity’-> palpitation, tremor, anxiety

Question 6

Thyroid hormones

Answer 6

Healthy adult thyroid gland secretes T4 and T3

Question 7

T4

Answer 7

• otherwise known as Thyroxine or Tetraiodothyronine
• prohormone
• T4 converted by deiodinase enzyme into the more active metabolite triiodothyronine (T3)

Question 8

T3

Answer 8

• otherwise known as triiodothyronine
• 80% of circulating T3 from deiodination of T4
• 20% of circulating T3 from direct thyroidal secretion
• T3 provides almost all thyroid hormone activity in target cells

Question 9

Thyroid hormone replacement therapy

Answer 9

1) Levothyroxine sodium

2) Liothyronine sodium