The diuretic spironolactone can cause dangerous hyperkalaemia in patients who are also taking angiotensin converting enzyme (ACE) inhibitors, another drug that, like spironolactone, is used to treat congestive heart failure.

After the publication of a major heart study that promoted the use of spironolactone, prescribing rose, but so did cases of hyperkalaemia, according to Dr David Juurlink, a clinical pharmacologist at the University of Toronto and author of a new study that found a threefold increase in the rates of admission to hospital for high potassium levels across Ontario and a twofold increase in deaths involving high potassium levels (New England Journal of Medicine 2004;351:543-51).

The randomised aldactone evaluation study (RALES), which was reported in 1999, found …