Thyroxine

Question 1

What is the generic and brand name of thyroxine?

Answer 1

• Levothyroxine (Eltroxin)

Question 2

What is the method of action of thyroxine?

Answer 2

T4 (inactive) → T3 (active)
• = regulates metabolism and growth
• Drug is a synthetic replacement of T4

Question 3

What are the indications for thyroxine?

Answer 3

• Primary hypothyroidism

* Hypothyroidism secondary to hypopituitarism

Question 4

What are the contraindications for thyroxine?

Answer 4

• Coronary artery disease – start on low dose and monitor
• Hypopituitarism – corticosteroid therapy must be initiated before thyroid hormone to avoid precipitating an Addisonian crisis

Question 5

What are the side effects of thyroxine?

Answer 5

• GI upset
• Weight loss
• Palpitations
• Arrhythmias
• Angina
• Tremor
• Restlessness
• Insomnia

Question 6

What organ eliminates thyroxine?

Answer 6

Kidney

Question 7

What information should be given to a patient taking thyroxine?

Answer 7

• May take time to work
• Do not stop taking the medication
• Leave 4 hours gap between calcium or iron replacements

Question 8

What drugs interact with thyroxine?

Answer 8

• Antacids - ↓ GI absorption so drugs need to be separated from each other by about 4 hours
• Calcium salts - ↓ GI absorption so drugs need to be separated from each other by about 4 hours
• Iron salts - ↓ GI absorption so drugs need to be separated from each other by about 4 hours
• Cytochrome P450 inducers e.g. phenytoin, carbamazepine – dose may need to be ↑
• Insulin - ↑ requirement
• Hypoglycaemic drugs - ↑ requirement
• Warfarin – enhances affects