Endocrine
Fludrocortisone
A mineralocorticoid — Replaces the salt-retaining hormone in adrenal insufficiency and helps some low blood pressure.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
Quick answer
What is Fludrocortisone?
Fludrocortisone replaces the mineralocorticoid hormone (aldosterone) that controls salt, water and potassium balance. It is used mainly in primary adrenal insufficiency alongside steroid replacement, and sometimes for low blood pressure on standing.
- How it works: It acts like aldosterone, telling the kidneys to hold on to sodium (and water) and to excrete potassium.
- In practice: In practice fludrocortisone supplies the salt-and-water-retaining (mineralocorticoid) hormone that the adrenal glands fail to make in primary adrenal insufficiency (Addison's disease), where it is given alongside a steroid such as hydrocortisone.
What it is
Fludrocortisone replaces the mineralocorticoid hormone (aldosterone) that controls salt, water and potassium balance. It is used mainly in primary adrenal insufficiency alongside steroid replacement, and sometimes for low blood pressure on standing.
How it works
It acts like aldosterone, telling the kidneys to hold on to sodium (and water) and to excrete potassium. This restores normal salt and fluid balance and supports blood pressure in people who cannot make enough of their own.
In practice
In practice fludrocortisone supplies the salt-and-water-retaining (mineralocorticoid) hormone that the adrenal glands fail to make in primary adrenal insufficiency (Addison's disease), where it is given alongside a steroid such as hydrocortisone. It is also used in some causes of low blood pressure on standing. Its effects are essentially an extension of its job: it raises blood pressure and can cause fluid retention, swelling and a fall in potassium, so blood pressure, fluid status and potassium are monitored, and the dose is adjusted using these together with how the patient feels. People on adrenal replacement also need the usual "sick-day" steroid rules and an emergency plan, and should carry a steroid alert card — fludrocortisone does not replace the steroid component or the need to increase steroid cover in illness.
Examples
Practical use
How to take it & use it well
- Take fludrocortisone as prescribed, usually once daily, and at the same time each day to keep levels steady.
- In Addison's disease it is taken alongside a steroid such as hydrocortisone - it does not replace that steroid, so keep taking both as directed.
- Carry a steroid alert card and follow your sick-day rules for the steroid part of your treatment during illness, injury or surgery.
- If you miss a dose, take it when you remember unless it is nearly time for the next one; do not double up, and ask your clinician if unsure.
- Attend reviews so your blood pressure, fluid balance and potassium can be monitored, and do not stop it suddenly without advice.
Common uses
- Primary adrenal insufficiency / Addison's disease (with a steroid)
- Some forms of postural (orthostatic) hypotension
- Salt-losing congenital adrenal hyperplasia (specialist)
Monitoring
- Blood pressure, fluid status (swelling/weight) and potassium
- Symptoms of under- or over-replacement
- Adjustment alongside the steroid component
Weighing it up
Advantages & disadvantages
Advantages
- It replaces the salt-regulating hormone the body lacks in Addison's disease, helping maintain blood pressure and fluid balance.
- It can help some people with low blood pressure on standing (postural hypotension).
- It is taken once daily, which is simple to fit into a routine.
- Used correctly with steroid replacement, it supports stable everyday wellbeing.
Disadvantages
- It can cause fluid retention, raised blood pressure and low potassium, which need monitoring.
- It does not provide the steroid (glucocorticoid) cover needed in illness, so sick-day rules and extra steroid are still essential.
- Stopping it abruptly or skipping doses can upset salt and fluid balance.
- It needs ongoing blood pressure and blood-test checks to stay correctly dosed.
Key safety principles
What to watch for
- Can cause fluid retention, raised blood pressure, swelling and low potassium — monitor these.
- Does not replace glucocorticoid (steroid) cover — sick-day rules and dose increases in illness still apply.
- Carry a steroid alert card and have an emergency plan for adrenal crisis.
Key interactions
What to avoid or check alongside
- Water tablets (diuretics) and other medicines that lower potassium can worsen low potassium when combined with fludrocortisone.
- Medicines for high blood pressure may be less effective because fludrocortisone can raise blood pressure and cause fluid retention.
- NSAID pain relievers can add to fluid retention and raised blood pressure.
- Low potassium can increase the risk of toxicity from heart medicines such as digoxin, so levels are monitored.
Patient & carer advice
- This is one part of your replacement — keep taking your steroid too, and increase it when ill as advised
- Carry your steroid card and know your emergency injection plan
- Report swelling, breathlessness or muscle weakness
Use with
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Answers
Fludrocortisone: frequently asked questions
Does fludrocortisone replace my hydrocortisone?
No. Fludrocortisone replaces the salt-regulating hormone, while hydrocortisone provides the steroid your body needs. In Addison's disease you usually need both, and must keep taking each as prescribed.
Do sick-day rules apply to fludrocortisone?
Sick-day rules mainly mean increasing your steroid (such as hydrocortisone) during illness, not the fludrocortisone. Follow the plan your clinician gave you and seek help if you are very unwell.
Why do I need blood tests on this medicine?
Fludrocortisone can raise blood pressure and lower potassium and cause fluid retention. Regular checks of blood pressure and potassium help keep your dose right and safe.
Why do I need a steroid alert card?
It tells healthcare staff that you depend on steroid replacement, which is vital in an emergency, illness or surgery. Carry it at all times alongside your treatment.
Can I stop fludrocortisone if I feel well?
No - do not stop it suddenly. Your body relies on it for salt and fluid balance, so any changes should only be made on your clinician's advice.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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