Thyroxine

Question 1

Patient communication - what is hypothyroidism and how will levothyroxine help me?

Answer 1

The thyroid gland in your neck makes a hormone called thyroxine. Thyroxine controls how much energy your body uses (the metabolic rate). It’s also involved in digestion, how your heart and muscles work, brain development and bone health.

When the thyroid gland does not make enough thyroxine (called hypothyroidism), many of the body’s functions slow down. Some of the most common symptoms of an underactive thyroid gland are:

• tiredness
• feeling cold
• difficulty concentrating
• weight gain
• feeling depressed

Levothyroxine is a synthetic version of thyroxine. You take levothyroxine tablets to replace the thyroxine that your thyroid gland cannot produce and prevent the symptoms of hypothyroidism.

Question 2

Levothyroxine - indication

Answer 2

1. Primary Hypothyroidism (high TSH, low T4)

2. Hypothyroidism secondary to hypopituitarism (low TSH, low T4)

Question 3

Which patients usually require a lower starting dosage of levothyroxine?

Answer 3

1. anyone over 65 years old basically

2. 50 or over with CVD

Question 4

Levothyroxine - monitoring

Answer 4

• Repeat TFTs after 8-12 weeks
• TSH levels are more sensitive than T4 levels for monitoring patients with existing thyroid problems and are often used to guide treatment

once effective dose is achieved this is maintained.

Question 5

A woman with hypothyroidism comes in asking for advise as she is planning on getting pregnant - what do you need to advise her regarding her medication?

Answer 5

• Women with known hypothyroidism should be euthyroid before becoming pregnant.

Question 6

Levothyroxine - side effects

Answer 6

1. Symptoms of Hyperthyroidism :

Diarrhoea

Nausea

Vomiting

Weight loss

2. Cardiac: palpitations, angina
3. Bone : Osteoporosis if overuse
4. Neuro: tremor

Question 7

How can levothyroxine result in osteoporosis?

Answer 7

This is because thyroid hormones lead to increased activity of osteoclasts and bone resorption = osteoporosis

Question 8

Levothyroxine - interactions and patient advice

Answer 8

1. Iron AND Calcium carbonate - reduce absorption of levothyroxine, give at least 4 hours apart.
2. Levothyroxine must be taken 30 minutes before food as it’s absorption may be affected by food, caffeine or other medications.

Other interactions:

• carbamazepine
• insulin
• warfarin

Question 9

Patient communication on administration of levothyroxine

Answer 9

Take levothyroxine once a day in the morning, ideally at least 30 minutes before having breakfast.

Food and caffeinated drinks can both stop your body taking in levothyroxine properly so it does not work as well.

Question 10

Levothyroxine - Cautions (2)

Answer 10

1) CAD: start at lower dose

2) Hypopituitarism: steroid therapy prior to thyroid hormone replacement

Question 11

Levothyroxine - MOA

Answer 11

Usually the thyroid gland produces T4 (thyroxine) which acts to regulate metabolism and growth.

Levothyroxine is a synthetic form of thyroxine (T4) and therefore replaces the deficiency.

Question 12

When is liothyronine (T3) used over levothyroxine (T4)?

Answer 12

During acute episode sof hypothyroidism

Why? Liothyronine has a shorter half-life and quicker onset - therefore it is reserved for emergencies