Thyroid hormones - Levothyroxine

Question 1

Thyroid hormones T3 and T4 are secreted from the thyroid. Primary hypothyroidism is when the thyroid is not secreting sufficient thyroid hormones. What is the name of the 1st line medication to treat this?

1 - Levothyroxine
2 - Carbimazole
3 - Teriparatide
4 - Cholecalciferol

Answer 1

1 - Levothyroxine

Question 2

Levothyroxine is the 1st line medication for hypothyroidism that is a synthetic form of thyroxine (T4) that acts the same way as normal T4. Which 2 of the following is Levothyroxine indicated in the use of?

1 - primary hypothyroidism
2 - tertiary hypothyroidism
3 - secondary hypothyroidism
4 - hypothyroidism secondary to hypopituitarism

Answer 2

1 - primary hypothyroidism

4 - hypothyroidism secondary to hypopituitarism

Question 3

The adverse effects of Levothyroxine are generally due to larger doses. Which of the following is NOT a common adverse event of Levothyroxine?

1 - weight gain
2 - GI upset
3 - palpitations/arrhythmias
4 - tremors/restlessness
5 - insomnia

Answer 3

1 - weight gain
- typically weight loss
- effects are what we could see in hyperthyroidism

Question 4

In a patient with coronary artery disease, why does Levothyroxine need to be prescribed at a lower dose and slowly titrated up with monitoring?

1 - increases palpitations
2 - increases cardiac workload
3 - increases risk of ischaemia
4 - all of the above

Answer 4

4 - all of the above

Question 5

In a patient with hypopituitarism what drug class should be started in patients prior to commencing Levothyroxine?

1 - ACE-I
2 - glucocorticoids
3 - mineralcorticoids
4 - loop diuretics

Answer 5

2 - glucocorticoids
- thyroid hormones increase hepatic metabolism of glucocorticoids
- adrenal insufficiency = glucocorticoids
- increases metabolism of glucocorticoids could therefore lower levels further and cause adrenal crisis (Addisons crisis

Question 6

Which of the following medications/supplements should be avoided in patients taking Levothyroxine?

1 - calcium supplements
2 - antacids
3 - iron supplements
4 - all of the above

Answer 6

4 - all of the above

• all inhibit the absorption of Levothyroxine
• need a 4 hour gap between these and Levothyroxine OR a higher dose of Levothyroxine

Question 7

Why must we be careful if a patient is taking any of the following when prescribing Levothyroxine?

• carbamazapine
• rifampin
• alcohol
• phenytoin
• griseofulvin
• phenobarbital
• sulphonylureas

1 - can increase toxicity and induce liver failure
2 - can induce acute kidney damage
3 - increased metabolism and less efficacy
4 - decreased metabolism and increased efficacy and risk of adverse events

Answer 7

3 - increased metabolism and less efficacy

• all drugs are cytochrome P450 inducers, so may need larger Levothyroxine dose
• CRAP GPS is the mnemonic

Question 8

Can Levothyroxine improve or worsen glycemic control?

Answer 8

• can increase secretion of insulin and glucagon
• can lead to worse glycemic control

Question 9

How is the dose of Levothyroxine typically calculated?

1 - 1.6 micrograms per kg if < 65
2 - 3 micrograms per kg if < 65
3 - 6 micrograms per kg if < 65
4 - 10 micrograms per kg if < 65

Answer 9

1 - 1.6 micrograms per kg if < 65

Question 10

What is a typical starting dose of Levothyroxine?

1 - 5-10micrograms OD PO
2 - 20-30micrograms OD PO
3 - 50-100micrograms OD PO
4 - 500-1000micrograms OD PO

Answer 10

3 - 50-100micrograms OD PO

• taken orally

Question 11

The typical starting dose of Levothyroxine is 50-100micrograms OD PO. However what should be the starting dose in an older patient or one with cardiac disease?

1 - 5-10micrograms OD PO
2 - 25-50micrograms OD PO
3 - 50-100micrograms OD PO
4 - 500-1000micrograms OD PO

Answer 11

2 - 25-50micrograms OD PO

• taken orally

Question 12

To monitor the effects of Levothyroxine, which of the following should be measured?

1 - thyroxine (T4)
2 - triiodothyronine (T3)
3 - thyroid stimulating hormone (TSH)
4 - T3 resin uptake (T3RU)
5 - all of the above

Answer 12

5 - all of the above
- part of normal thyroid panel in hospital

• T3RU is a measure of proteins that carry T4 in blood

Question 13

How often are adults taking Levothyroxine monitored for their thyroid hormones once TSH is stable?

1 - 3 monthly
2 - 6 monthly
3 - annually
4 - every 2 years

Answer 13

3 - annually

Children > 2 years: once TSH stabilised every 4-6 months until puberty then annually
Children < 2 years: once TSH stabilised every 2-3 months in 1st year, 3-4 months in 2nd year

Question 14

Do patients thyroid requirements go up or down during pregnancy?

Answer 14

• up
• human chorionic gonadotropin (hCG) and estrogen increase thyroid hormone levels in the blood
• baby needs iodine, which is what thyroid hormones contain

Question 15

Do the blood results attached indicate hypo or hyperthyroidism?

Answer 15

• hypothyroidism
• high TSH, BUT low T3 and T4
• indicates primary hypothyroidism