Drinking “plenty of fluids” may cause worsening symptoms and potential fatalities for patients with reduced renal function, a BMJ case report has revealed.

Health professionals often advise patients to “drink plenty of fluids” and “keep well hydrated” when ill, but the authors of the report call for more research behind this advice.

The report, ‘When plenty is too much’, detailed the case of a patient who became severely unwell from drinking too much water while in treatment for a urinary tract infection (UTI).

The 59-year-old woman developed hyponatraemia (an unhealthily low level of sodium) from drinking too much water, based on previous medical advice, to help with a recurring UTI.

The patient was admitted to the Royal London Hospital A&E, and was prescribed antibiotics and painkillers for her infection. However, she became progressively shaky, muddled, vomited several times, and had significant speech difficulties.

Tests revealed hyponatraemia – her sodium level was 123 mmol/L (normal range 135-145) – which caused her progressively worsening symptoms.

The patient’s condition was caused by water intoxication.She revealed that throughout the day, she had consumed several litres of water based on medical advice she recalled from previous similar episodes to “flush out her system”.

The condition is a medical emergency and requires prompt recognition and action, the report said. A mortality rate of almost 30% has been reported for patients with sodium levels of less than 125 mmol/L.

The woman’s fluid intake was restricted to 1 litre over the following 24 hours, and by the following morning she felt improved, her blood tests were normal, and she was ready to be discharged.

Fatal water intoxication has also been reported in endurance exercise, use of the drug MDMA, and anecdotally during university initiation activities as well as during water-based torture rituals.

The report revealed that the incident mirrors a previous case report, in which a woman developed hyponatraemia and later died from drinking excessive amounts of water during an episode of gastroenteritis.

It is very rare to develop water intoxication with normal renal function. However, some illnesses drive up levels of antidiuretic hormones, which reduce renal excretion of water. The case report questioned whether drinking increased water should be recommended in these situations.

The case report concluded: “There is a paucity of evidence behind the advice to ‘drink plenty of fluids’ in the management of mild infective illness. This needs to be addressed, especially considering the significant morbidity and mortality of acute hyponatraemia."

How will the new pharmacy funding package impact on you? Take part in our survey and be in with a chance of winning £100 in John Lewis vouchers.