Spironolactone: NHS information, uses and monitoring

Spironolactone is an aldosterone antagonist. It is also called a potassium-sparing diuretic. It blocks aldosterone, a hormone from the adrenal glands.

Aldosterone tells kidneys to keep salt and water, and to release potassium. Spironolactone blocks aldosterone receptors in the kidney. This helps the body remove extra salt and fluid.

It also holds on to potassium. This is the opposite of loop diuretics like furosemide, or thiazides like bendroflumethiazide.

Aldosterone does more than control fluid. In heart failure, high aldosterone levels can scar and stiffen the heart muscle and blood vessels. Spironolactone blocks this effect.

This is one reason it improves survival in heart failure. This benefit is beyond its mild diuretic action.

Spironolactone also has anti-androgenic effects. It partly blocks receptors for male-type hormones (androgens). It also reduces their production. Some patients do not want this effect.

However, dermatologists and GPs use it off-label for hormonal acne and excess hair growth in women. This is precisely because of this property.

In the UK, spironolactone is a prescription-only medicine (POM). It comes as 25 mg, 50 mg, and 100 mg tablets. An oral suspension is also available.

The original brand name, Aldactone, is still sometimes used. However, most NHS prescriptions are for generic spironolactone. It is usually taken once daily with food. This helps reduce stomach upset.

It is often combined with other heart or blood pressure medicines. This requires careful monitoring.

Spironolactone has several established NHS uses. It also has widely accepted off-label uses:

• Heart failure with reduced ejection fraction. Low-dose spironolactone is added to standard treatment. It reduces hospital admissions and improves survival. NICE guidance strongly recommends it for moderate to severe heart failure.
• Resistant hypertension. Blood pressure may stay high despite three medicines. These are usually an ACE inhibitor or ARB, a calcium channel blocker, and a thiazide-like diuretic. NICE recommends low-dose spironolactone as the usual fourth-line option. This is if blood potassium is not already high.
• Oedema and ascites in liver cirrhosis. Spironolactone counters the high aldosterone levels common in cirrhosis. It is the first-choice diuretic for ascites. Sometimes, high doses are used under specialist care.
• Nephrotic syndrome and other oedema. This is when excess aldosterone plays a role.
• Primary hyperaldosteronism (Conn's syndrome). It is used both before surgery and as long-term treatment if surgery is not suitable.

Off-label, spironolactone is often prescribed for hormonal acne, hirsutism (excess hair growth), and polycystic ovary syndrome symptoms in women. Doses are usually 50-100 mg daily.

"Off-label" means the use is not on the official licence. However, clinical experience and specialist guidance support it. Your prescriber should explain this when you start treatment.

It is not used for these purposes in men. This is due to its feminising side effects.

Doses vary greatly depending on the condition. Typical adult regimens in the BNF include:

• heart failure: 25 mg once daily. This may increase to 50 mg or reduce to 25 mg on alternate days. This depends on response and blood test results.
• resistant hypertension: 25 mg once daily (off-label at this dose).
• ascites in cirrhosis: starts at 100 mg daily. It can be increased up to 400 mg in specialist care.
• acne or hirsutism (off-label): usually 50-100 mg daily.

Spironolactone needs regular blood tests. This makes it different from many other tablets. It can cause potassium retention and affect kidney function.

UK practice is to check urea and electrolytes (U&Es).

• before starting treatment.
• about 1 week after starting or after any dose change.
• monthly for the first three months.
• then every three months for a year.
• and at least every six months long term, or more often if you are unwell.

Your GP surgery will usually call you for these tests. Do not skip them. A dangerously high potassium level often causes no symptoms. It may only affect heart rhythm later.

Take the tablets with food, preferably in the morning. This way, the diuretic effect does not disturb your sleep. If you become acutely unwell with vomiting, diarrhoea, or dehydration, seek guidance.

NHS "sick day" advice is to temporarily pause spironolactone. Dehydration sharply increases the risk of kidney injury and high potassium.

The main risk with spironolactone is hyperkalaemia. This is a high blood potassium level. Potassium is vital for a normal heart rhythm. However, too much can cause dangerous arrhythmias.

In severe cases, it can lead to cardiac arrest. Hyperkalaemia often develops without symptoms. This is why blood test monitoring is essential.

Possible warning symptoms include muscle weakness, an irregular or slow heartbeat, tingling, and extreme tiredness. Seek urgent medical advice if these occur.

The risk of hyperkalaemia is higher if you:

• have chronic kidney disease or worsening kidney function.
• also take an ACE inhibitor (like ramipril) or an ARB (like candesartan or losartan). This is a common and usually planned combination in heart failure. However, it needs closer monitoring.
• take potassium supplements or use potassium-containing salt substitutes like LoSalt. These should generally be avoided.
• are older, diabetic, or dehydrated.
• take NSAIDs like ibuprofen regularly. These can further harm kidney function.

Spironolactone should not be used if you have severe kidney failure, Addison's disease, or an existing high potassium level. Caution and specialist advice are needed for significant liver disease.

However, cirrhosis with ascites is a key reason for its use.

In pregnancy, spironolactone is generally avoided. Its anti-androgenic action could theoretically affect a male foetus. Women taking it for acne or hirsutism should use reliable contraception.

They should tell their doctor promptly if they become pregnant. Trimethoprim, a common antibiotic for urine infections, can also raise potassium.

It is best avoided or used with extra monitoring during spironolactone treatment.

Beyond hyperkalaemia, the best-known side effect of spironolactone is gynaecomastia. This is breast tissue enlargement or tenderness in men. It depends on the dose. It is uncommon at 25 mg daily.

However, it affects many men on higher long-term doses. It usually improves after stopping the medicine. This can take months.

If gynaecomastia is a problem in heart failure treatment, doctors can often switch. They may use eplerenone, a similar aldosterone antagonist. It has much less effect on hormone receptors.

In women, hormonal effects can include breast tenderness and irregular periods. This means spotting or changes in cycle length.

This is important for women taking spironolactone off-label for acne. Combining it with a combined oral contraceptive often stabilises periods.

It also provides the contraception advised during treatment.

Other known side effects include:

• dizziness or light-headedness, especially when standing. This is due to lower blood pressure or mild dehydration.
• increased urination, particularly when starting treatment.
• nausea or stomach upset. Taking tablets with food helps.
• headache, drowsiness, and leg cramps.
• raised creatinine or sodium disturbance on blood tests.
• rarely, rash or, very rarely, severe skin reactions.

Most side effects are mild. They settle as your body adjusts. Contact your GP if dizziness causes falls or near-fainting.

Also, if you notice worrying breast changes, or develop muscle weakness or palpitations. Do not stop spironolactone suddenly if you take it for heart failure or cirrhosis.

This is unless a doctor advises it. Your underlying condition can quickly worsen.

Spironolactone is a prescription-only medicine (POM) in the UK. GPs and hospital specialists prescribe it.

It cannot be sold over the counter or by online sellers without a prescriber's assessment. In England, the standard NHS prescription charge applies. This is unless you qualify for an exemption.

A prescription prepayment certificate (PPC) can lower costs. This is if you take several regular medicines. Prescriptions are free in Scotland, Wales, and Northern Ireland.

Before you start, your prescriber should:

• check baseline U&Es and kidney function.
• review all your medicines for interaction risks. These include ACE inhibitors, ARBs, NSAIDs, trimethoprim, potassium supplements, digoxin, and lithium. Spironolactone can affect their levels.
• explain the monitoring schedule. They should also explain what symptoms need urgent review.
• discuss contraception if spironolactone is used off-label for acne or hirsutism.

Tell every clinician who treats you that you take spironolactone. This includes dentists and pharmacists. Avoid buying potassium-containing salt substitutes or high-dose supplements without advice.

Report suspected side effects via the MHRA Yellow Card scheme.

For reliable further reading, the NHS website has patient-friendly information on spironolactone. The BNF by NICE outlines dosing and monitoring for UK prescribers.

The electronic medicines compendium (EMC) at medicines.org.uk hosts the official Patient Information Leaflet and Summary of Product Characteristics for each licensed spironolactone product.

Your community pharmacist can also answer daily questions about taking it safely.