More monitoring needed for patients taking diuretics

One in five patients taking diuretics commonly prescribed for high blood pressure or heart conditions end up with reduced sodium and potassium levels, according to a study published in the January issue of the British Journal of Clinical Pharmacology.

But as few as a third of patients on the drugs have their electrolyte levels tested - despite the fact that reduced levels can lead to a wide range of health problems.

A team from The University of Nottingham and Queen's Medical Centre reviewed the records of more than 32,000 adults from six general practices in the East Midlands.

They found that almost one in eight had received at least one prescription for thiazide diuretics between 1990 and 2002, but only 32 per cent had had their sodium and potassium levels recorded electronically. The drug most commonly prescribed was bendroflumethiazide (bendrofluazide).

Some 21 per cent - one in five - of those who had been tested had levels that fell below the normal range.

"In a small number of patients reduced sodium and potassium levels - often referred to as electrolyte levels - can be severe enough to require hospital admission, especially if they are elderly," said lead author Dr Jennifer Clayton.

"In milder cases they can make people feel below par, cause general weakness and tiredness and sometimes interfere with the normal rhythm of the heart.

"Severe loss of sodium can make it difficult for people to maintain their blood pressure at a normal level, causing dizziness, confusion and an increased risk of falls in older people.

"And loss of potassium can make people more susceptible to the side effects of other drugs they are taking for heart conditions."

Other findings included:

• Low sodium levels were much more common than low potassium levels. Of the 196 patients tested with low levels, 66 per cent had low sodium levels and 40 per cent had low potassium levels. A small number of patients had both.
  
• Nine per cent of the 196 patients tested with low levels had severe electrolyte disturbances - with ages ranging from 47 to 93. Ten of these were taken off the medication, but seven - including a 90 year-old male - were not.
  
• Patients who had severe electrolyte disturbances had taken the medication for three to 90 months before their levels were checked.
  
• 72 per cent of the 130 patients with low sodium levels were mild cases, 21 per cent were moderate and seven per cent were severe. Just over 80 per cent continued taking the drug, including a third of the severe cases.
  
• Patients taking thiazide diuretics ranged from 19 to 99 years-old and nearly half were between 60 and 79.
  
• 90 per cent were receiving the currently recommended dose of 2.5mg a day, but 10 per cent were receiving a higher dose.