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LONDON (Reuters Health) – Physicians should monitor the kidney function of elderly patients taking angiotensin converting enzyme inhibitors (ACE inhibitors) and non-steroidal anti-inflammatory drugs (NSAIDs) in combination, British researchers advise.

Dr. Vedamurthy Adhiyaman Glan Clwyd District General Hospital in Rhyl, Wales and colleagues found that the two drug classes, both known to affect renal function, caused acute renal failure in 2 of 12 patients taking both types of drugs in combination with diuretics.

Reporting their findings in the October edition of the Journal of the Royal Society of Medicine the investigators warn: "This drug combination is commonly nephrotoxic in the elderly and should be avoided."

However, sometimes physicians may have little choice but to prescribe both drugs at the same time, lead researcher Dr. Adhiyaman told Reuters Health. "Often, when you talk to the patient about it, they still want the drugs," he said. "Doctors need to keep an eye on them and carry out regular renal function tests."

Dr. Adhiyaman's group studied patients aged 75 or older, already on long-term treatment with one of the drugs, who were then prescribed the second drug. To qualify, patients had to have normal renal function at the start of their dual treatment.

During follow-up appointments at 6 and 12 weeks, each patient was tested for renal function again and the use of other medications was also taken into account, especially diuretics.

Over the period of 1 year, researchers identified 12 patients who had received the drugs in combination. Two developed acute renal failure after taking diuretics along with the drug combination. One patient died and the other recovered after both drugs were discontinued.

Four other patients, who were also taking diuretics, showed deterioration in renal function between 8 and 12 weeks. The remaining six subjects had normal renal function at 6 months, although researchers noted only two of these patients had been taking diuretics at the same time.

In most of those who subsequently stopped taking either their ACE inhibitors or NSAIDs renal function returned to normal.

"NSAIDs and ACE inhibitors are the main causes of drug-induced acute renal failure in the elderly," the researchers write. "Since sodium depletion is a precipitating factor, addition of a diuretic increases the risk of renal failure."

It is believed that the renal damage is caused by the combined effect of the drugs on the glomerular filtration rate, which is partly dictated by cardiac output and extent of vasoconstriction, they add.

However, it is known that NSAID therapy can affect production of prostaglandin–which helps to open up blood vessels–and so reduces the amount of blood filtered by the kidneys.

In addition, ACE inhibitors limit the degree of constriction in blood vessels, which means the pressure at which blood is pumped into the kidneys also falls. The added effects of the diuretics–which reduce blood volume and therefore pressure–means the kidneys are left functioning at a reduced rate of efficiency.

The researchers concede that the small numbers in their study may skew the findings, but said they are still convinced the combination is potentially dangerous for some elderly patients.