ARBs and potassium: supplements, salt substitutes and high potassium

The BNF describes ARBs, together with potassium chloride and other medicines, as able to increase the risk of hyperkalaemia, a higher than normal level of potassium in the blood. The NHS signs of high potassium include muscle weakness and an abnormal heartbeat, which is why a level that is too high is taken seriously.

The NHS ramipril page, written for another medicine from the same wider family, says that doctors will carry out blood tests before starting treatment and when the dose changes to check kidney function and potassium levels. The same logic applies to ARBs.

The BNF interaction list for losartan includes an entry for potassium chloride stating that both can increase the risk of hyperkalaemia, with the note that this is particularly notable when ACE inhibitors or angiotensin-II receptor antagonists are given with spironolactone or eplerenone. The candesartan list and the potassium chloride list carry matching entries.

The NHS losartan page says there are medicines and supplements that may not mix well with losartan, naming supplements and salt substitutes containing potassium, some diuretics such as spironolactone, some NSAIDs, fluconazole, tricyclic antidepressants, antipsychotics such as quetiapine and lithium. The NHS candesartan page lists the potassium point in nearly the same way, adding heparin.

Potassium chloride tablets prescribed by a doctor are one source, and the doctor will have considered the combination. Others are easier to miss. The NHS eplerenone page notes that salt substitutes can contain potassium and that some multivitamin and mineral supplements contain potassium, so labels are worth reading.

The NHS pages for related medicines say some salt substitutes may increase potassium levels, which is why a person advised to cut down on salt may need a pharmacist's view on substitutes while taking an ARB.

• Salt substitutes and low-sodium salt products.

• Potassium supplements and some multivitamin and mineral products.

• Potassium-sparing diuretics such as spironolactone or amiloride.

• Other medicines that raise potassium, such as trimethoprim.

The NHS trimethoprim page lists muscle weakness, an abnormal heartbeat or chest pains as signs of high potassium in the blood and advises calling 999 or going to A&E and not driving yourself. The NHS eplerenone page describes muscle cramps and diarrhoea as possible effects of raised potassium with that medicine.

High potassium can cause no symptoms at first, which is why blood tests matter. If a test shows a high level the prescriber will decide what to change. Do not adjust your medicines on the basis of a single result you have read without advice.

The NHS candesartan page says you may need to take it for many weeks, months or years to manage your condition, and not to stop without talking to your doctor because your condition may get worse without the medicine. If your doctor thinks you should stop, they will help you reduce the dose gradually. The practical message is that a potassium concern is dealt with by reviewing the supplements, salt substitutes and other medicines around the ARB, with the prescriber, rather than by dropping the ARB.

Both NHS pages also remind readers that their lists are not the full list of medicines that may not mix well, so the pharmacist's check of a new product is worth having each time.

GP practices and community pharmacists can review supplements and salt substitutes alongside your blood pressure medicine, and a potassium blood test can be arranged through the GP. This site has a separate guide to the potassium blood test. Private services use the same references, so give them the full list.