Eplerenone: heart failure medicine, monitoring and cautions

Eplerenone is a type of medicine known as an aldosterone-blocking agent. Aldosterone is a hormone that makes the body retain salt and water; by blocking its effects eplerenone helps the heart work better and helps to prevent heart failure getting worse.

The NHS describes it as a treatment for heart failure that is probably needed for the rest of your life. Because the benefit is in slowing progression, you should keep taking it even if you do not notice a change in symptoms.

The NHS says the usual starting dose is 25mg once a day, and a doctor may increase it to 50mg once a day depending on your blood potassium. Take it at the same time each day, with or without food.

If you forget a tablet, take it that same day when you remember. If you miss the entire day, skip it and carry on the next day, and never take two at once. An overdose can cause nausea, vomiting, dizziness, confusion, tingling, cramps and a fast or irregular heartbeat. Call 111 for any overdose, and 999 or A&E for chest pain or an irregular or fast heartbeat.

Most adults aged 18 and over can take eplerenone. It is unsuitable if you have had an allergic reaction to it, or if you have liver or kidney disease, type 2 diabetes or raised potassium in the blood. A blood test is needed before you start.

The prescriber will check your kidney function and potassium and decide whether it is safe for you. Report all your conditions and medicines.

Common effects, affecting more than 1 in 100 people, include dizziness, headaches, difficulty sleeping, coughing, and nausea or vomiting. If you feel dizzy, stop what you are doing and sit or lie down until it passes, and do not drive, ride a bike or use machinery.

Less often it can disturb the body's salts. Contact your doctor or NHS 111 for muscle cramps, diarrhoea, weakness or nausea that may point to high potassium, for reduced urine, dark urine, thirst or dizziness suggesting dehydration, and for symptoms that could mean kidney trouble. Call 999 for an irregular or fast heartbeat, chest pain, or signs of a serious allergic reaction.

The NHS lists many medicines that interact, among them ramipril, enalapril, losartan and candesartan; tacrolimus and ciclosporin; trimethoprim, clarithromycin, erythromycin and rifampicin; HIV medicines; digoxin and amiodarone; lithium; diclofenac, ibuprofen, naproxen and aspirin; itraconazole and fluconazole; phenytoin, carbamazepine and phenobarbital; spironolactone and amiloride; and warfarin.

Potassium supplements are strictly to be avoided, as are salt substitute tablets and multivitamins containing potassium. St John's wort can affect how eplerenone works. The NHS says there is not enough information to confirm other herbal remedies are safe.

Avoid alcohol at first and after a dose increase, as it adds to the blood-pressure-lowering effect and may cause dizziness. Eplerenone is occasionally prescribed in pregnancy for some medical conditions, so discuss risks and benefits with your doctor. If your baby is healthy it can be used while breastfeeding, though other medicines might be better. There is no evidence it affects fertility.

Do not stop without medical advice, as heart failure may get worse. Regular blood tests check your mineral balance and especially potassium. The only similar medicine, the NHS says, is spironolactone, which carries a higher side-effect risk because it blocks other hormones too.