ACE inhibitors, potassium-raising diuretics and high potassium (hyperkalaemia)

Potassium is a mineral the body needs for nerves, muscles and the rhythm of the heart. The kidneys keep the level in a narrow range by removing any excess in urine. Both too little and too much can cause trouble, and a high level in particular can interfere with the electrical activity of the heart.

The NHS spironolactone page explains that the medicine can sometimes raise potassium levels and cause hyperkalaemia, and lists symptoms including muscle weakness, tiredness, numbness and an irregular heartbeat. Often there are no symptoms until the level is quite high, which is why blood tests are part of routine monitoring.

ACE inhibitors such as ramipril and lisinopril can themselves raise potassium. The BNF entry for ramipril lists a group of medicines that can increase the risk of hyperkalaemia when combined with it: amiloride, eplerenone, potassium chloride, spironolactone, triamterene and trimethoprim. It adds that hyperkalaemia is particularly notable when ACE inhibitors or angiotensin-II receptor antagonists are given with spironolactone or eplerenone.

The NHS ramipril page gives the patient version: tell your doctor if you take medicines that can increase the amount of potassium in your blood, such as spironolactone, triamterene, amiloride and potassium. The NHS lisinopril page lists diuretics such as bendroflumethiazide among medicines that may not mix well with it.

It is important to separate two types of diuretic. Potassium-sparing diuretics such as spironolactone, amiloride and triamterene tend to raise potassium. The BNF lists furosemide and bendroflumethiazide with ramipril for a risk of low blood pressure rather than as potassium-raising combinations.

The NHS spironolactone page makes a point that applies to ACE inhibitors too: eating foods like bananas and avocados, or using salt substitutes such as Lo-Salt, can raise potassium levels further. Salt substitutes are an easy thing to miss because they are marketed as a healthier option for people with high blood pressure.

• Salt substitutes and low-sodium salts, which often replace sodium with potassium.

• Potassium supplements and some multivitamin or mineral products.

• Large amounts of high-potassium foods such as bananas and avocados, if your doctor has warned you about potassium.

• Non-steroidal anti-inflammatory painkillers, which the BNF also lists as increasing the risk of hyperkalaemia with ramipril.

• The antibiotic trimethoprim, which the BNF lists as increasing the risk of hyperkalaemia with ramipril.

Mild hyperkalaemia often produces nothing you can feel. The NHS spironolactone page lists muscle weakness, tiredness, numbness and irregular heartbeat as possible features of high potassium, and advises calling NHS 111 if you think you are having serious side effects.

A pounding, very fast or irregular heartbeat, fainting or chest pain are emergencies; call 999. Do not wait for a routine blood test if you have these symptoms.

The NHS ramipril page also lists kidney problems signs, namely swollen ankles, blood in the pee or not peeing at all, as reasons to call a doctor or 111 now.

The NHS says that, to decide the right ramipril dose, your doctor will check your blood pressure and may arrange blood tests for kidney function and potassium. If you are asked to attend for a blood test, go, because the result may change what is prescribed.

When you are ill, the NHS ramipril page says to contact your doctor if you have a high temperature, sweating and shaking, vomiting or severe diarrhoea, because they may advise you to stop ramipril until you feel better and are eating and drinking normally.

Do not stop an ACE inhibitor or a diuretic on your own because of something you read. Combinations of heart and blood pressure medicines are often chosen on purpose, and abrupt changes can carry their own risks. Instead, ask your prescriber whether a potassium check is due.

If you are prescribed trimethoprim for a urine infection, or you buy a salt substitute, mention your ACE inhibitor. NHS and private pharmacists use the same BNF information and can usually answer quickly.