ACE inhibitors and potassium: why the combination needs care

ACE inhibitors, including ramipril, lisinopril and enalapril, relax and widen blood vessels. The NHS describes lisinopril as a type of medicine called an ACE inhibitor that makes blood vessels relax and widen, which lowers blood pressure and makes it easier for the heart to pump blood. They are used for high blood pressure, after a heart attack, for heart failure and for some kidney problems.

Potassium is a mineral the body needs, but the level in the blood is kept within a fairly narrow range. The kidneys do much of the work of keeping it there. Because ACE inhibitors act on blood pressure and on the kidneys, the NHS pages for these tablets repeatedly mention blood tests that check kidney function and potassium. The interaction in this guide is the situation where another medicine, supplement or dietary product also pushes potassium upwards, so that the combined effect is larger than either would have alone.

This is not a reason to be frightened of ACE inhibitors. Many people take them for years, often together with other heart and kidney medicines, under regular monitoring. The point of knowing about the interaction is that the people most affected are often those who are already being closely watched, and that small practical habits, such as mentioning an over-the-counter supplement, make the monitoring more useful.

The NHS ramipril page says there are medicines that may affect the way ramipril works, including medicines that affect your kidneys, blood pressure or how much potassium is in your blood. It asks you to tell your doctor if you are taking any of them. The table below summarises what the NHS pages for ramipril, lisinopril and spironolactone actually list.

• The list is not complete. The NHS says these are not all the medicines that may cause problems with ramipril, and points to the leaflet inside the packet for the full list.

• Herbal remedies and supplements are less well studied. The NHS says there is very little information about taking them with ramipril because they are not tested in the same way as pharmacy and prescription medicines.

High potassium does not always cause symptoms, which is one reason blood tests are used. When it does, the NHS spironolactone page describes muscle weakness, tiredness, numbness and an irregular heartbeat. On the ramipril side effects page, the NHS lists signs that can point to kidney problems: swollen ankles, blood in the pee or not peeing at all, and advises calling a doctor or 111 now if these happen.

The same page says to call 999 or go to A&E for symptoms such as a faster heart rate with chest pain and tightness, shortness of breath and wheezing, signs of stroke, or swelling of the lips, tongue and face, which may be angioedema. Angioedema is a separate rare reaction to ACE inhibitors rather than a potassium problem, but it is worth recognising because the NHS says people with black skin have a higher chance of it.

Many of these symptoms are non-specific. Tiredness and weakness have countless causes. The practical message is not to diagnose yourself but to tell a clinician that you take an ACE inhibitor, and any other medicines, when you report them.

The NHS pages do not give a risk score, so it would be wrong to quote percentages. What they do show is the groups that need more checking. Kidney function and potassium are checked before ramipril is started and when the dose changes. People who take several heart or kidney medicines together are more likely to be on one of the potassium-raising items in the list above. Spironolactone, for example, is used for heart failure, oedema and resistant high blood pressure, and the NHS states you may not be able to take it if you have ever had high potassium or have severe kidney problems.

Illness also changes things. The NHS ramipril page says that if you get diarrhoea or vomiting from a stomach bug or illness you should tell your doctor, and that you may need to stop ramipril for a while until you feel better. The NHS lisinopril page lists kidney problems, which it says are checked with blood tests, among the common side effects. Dehydration and kidney strain are therefore the situations in which the combination matters most.

In UK practice, ACE inhibitors are generally started at a low dose and increased gradually. The NHS lisinopril page says a doctor may prescribe a low dose to start with and increase it over a few days or weeks to reduce the chance of side effects, and that you may have regular blood tests or other checks. A blood test for kidney function and potassium is usually done before treatment and again after changes, as the ramipril page states.

If a result shows potassium that is higher than expected, the response depends on the number, the symptoms, kidney function and the reason the medicine was prescribed. Options a prescriber may consider include reviewing other potassium-raising medicines, advising on diet, adjusting the dose, or switching to another type of medicine. These are decisions for the prescriber, who knows the whole picture. Nothing on the pages read for this guide suggests that people should adjust treatment themselves.

Keep an up-to-date list of everything you take, including over-the-counter pain relief, supplements and salt substitutes. The NHS ramipril page asks you to tell your doctor or pharmacist about any other medicines, including herbal remedies, vitamins or supplements.

Tell the pharmacist you take an ACE inhibitor before buying anti-inflammatory painkillers. The NHS lists NSAIDs among medicines to mention, while noting that low-dose aspirin at 75mg a day is safe with ramipril. If you are unwell with sickness or diarrhoea, contact your GP surgery or pharmacist for advice about the day-to-day dose rather than carrying on regardless or stopping without advice.

If you attend A&E or an out-of-hours service, take your medicines or a current list. The NHS advises bringing all the medicines you take when you go to A&E.

Medicines reviews and blood monitoring for ACE inhibitors are usually handled by the GP surgery, sometimes with a community pharmacist or a hospital specialist for heart failure or kidney disease. Pharmacists can answer medicine questions without an appointment. Private clinics can also arrange blood tests and consultations, but the prescriber who knows your history is best placed to decide what a result means for your treatment, so results should be shared with that clinician.