Thyroid Hormones Flashcards
Give an example of a thyroid hormone?
Levothyroxine
What is the mechanism of action of levothyroxine?
Replaces low level of thyroxine in patients with underachieve thyroid glands, which in turn suppresses high TSH by negative feedback
What are the symptoms of hypothyroidism?
- Lethargy
- Tiredness
- Weight gain
- Thinning of skin and hair
What is an over-replacement of thyroxine characterised by?
Normal thyroxine level with a low TSH level
What is the route of delivery of levothyroxine?
PO
What are the indications for thyroxine?
- Primary hypothyroidism
- As ‘replace’ element of ‘block and replace’ regimen for hyperthyroidism
- Goitre
- Hashimoto’s thyroiditis
- Thyroid carcinoma
- Hypopituitarism
- Pregnancy-related hypothyroidism
What are the contraindications to thyroxine?
Thyrotoxicosis
When should thyroxine be used with caution?
- Long-standing hypothyroidism
- Adrenal insufficiency
- Angina and cardiovascular disorders
What monitoring is required with thyroxine?
- Baseline ECG when starting drug
- TFTs
Why should a baseline ECG be done when starting thyroxine?
For comparison with future ECGs taken if patients develop cardiovascular side-effects from the thyroid hormone replacement
When should TFTs be done with thyroxine?
3 months after starting treatment or changing dose, and annual once stable
When should maternal thyroid function be assessed?
- Before conception
- Diagnosis of pregnancy
- During 2nd and 3rd trimester
- After delivery
What might need to happen to levothyroxine dose during pregnancy?
May need to be increased
What needs to be done if thyroxine dose is changed during pregnancy?
Increased monitoring of thyroid function
What should be considered with long-term treatment with thyroxine?
Consider supplementation with vitamin D
What might thyroxine interact with?
- Warfarin
- Antacids
- Calcium
- Iron salts
- CYP450 inducers
What might happen if warfarin is given with thyroxine?
Enhanced anticoagulant effect
How should you avoid concurrent use of thyroxine and antacids, calcium, and iron salts?
Maintaining 4 hour gap
What pneumonic can be used to remember CYP450 inducers?
PC BRAS
Phenytoin Carbamazepine Barbiturates Rifampicin Alcohol Sulphonylureas
What are the common side effects of thyroxine?
- GI upset
- Palpitations
- Tremor
- Angina
- Goitre
- Restlessness
- Flushing
- Headache
What are the less common side effects of thyroxine?
- Angina
- Muscular weakness
- Weight changes
- Insomnia
- Mood changes
What patient counselling is required with thyroxine?
- Mode of action
- How to take
- Duration of treatment and monitoring
- Dosing
- Compliance
- Signs of thyrotoxicosis
What should the patient be told about the mode of action of thyroxine?
Explain this medication contains a hormone that the patients body is not producing to an adequate level and as a result the patient is experiencing symptoms
What should the patient be told regarding how to take thyroxine?
Preferred to take levothyroxine in the morning 30 minutes to 1 hour before having breakfast or taking other medications
What should the patient told regarding duration of treatment with thyroxine?
Inform the patient that treatment is likely to be lifelong and that regular blood tests will be required to monitor thyroid function
What should the patient be told regarding dosing of thyroxine?
Thyroid hormone replacement is normally taken once daily. The patient will be started on the minimum dose, and the dose will be titrated up if required
What should the patient be told regarding compliance with thyroxine?
It is important the patient takes the drug as directed and that the patient does not stop taking the drug on their own initiative
What are the signs of thyrotoxicosis?
- Palpitations
- Arrhythmias
- Angina
- Tremor
- Diarrhoea
