06/03/2013 01:15 EDT | Updated 08/03/2013 05:12 EDT

Study suggests commonly used class of antibiotics linked to kidney damage

TORONTO - A new study says commonly used antibiotics called fluoroquinolones appear to increase a user's risk of developing kidney injuries.

The study says people taking the drugs have double the risk of developing kidney problems while they are on the medication than people who aren't taking these drugs.

The authors say that in actual numbers that means an additional case of kidney injury for every 1,529 people taking oral fluoroquinolones.

Drugs in this class include ciprofloxacin, gatifloxacin, gemifloxacin, levofloxacin, moxifloxacin and norfloxacin.

The study says this effect is not seen with other commonly used antibiotics like amoxicillin and azithromycin.

The research is published in this week's issue of the Canadian Medical Association Journal.

The researchers are from the U.S. Food and Drug Administration, the University of Florida in Gainesville, Fla., the therapeutic evaluative unit of the University of British Columbia in Vancouver, McGill University Health Centre in Montreal and the University of Washington in Seattle, Wash.

The research only looks at people taking the drugs orally; it does not include people receiving fluoroquinolones administered intravenously in hospital.

There have already been suggestions that these drugs may cause kidney problems. Renal failure is listed as an uncommon but potential side-effect on the labels of these antibiotics.

The study notes that there have been reports of tendon rupture and retinal detachment in people taking fluoroquinolones, which suggest the drugs may damage collagen and connective tissues.

The research suggests the effect is more profound for people who take these drugs while on another type of medication known as ACE-inhibitors — drugs used to treat high blood pressure, heart failure or diabetic kidney disease. For people using ACE-inhibitors and fluoroquinolones, the risk of developing kidney damage while on the antibiotics is nearly 4.5 times higher than people who aren't taking the drugs.

Dr. David Juurlink, a drug safety expert at Toronto's Sunnybrook Health Sciences Centre, says the study is well done and persuasive.

"It's still not going to be common," Juurlink, who was not involved in the study, says of the effect.

"(But) even if it's one in ... 1,500 patients, if suddenly these drugs are given to 1.5 million patients — and they are — you've got 1,000 extra patients with renal failure."

Juurlink says these drugs need to be prescribed in some circumstances, and he wouldn't hesitate to use them when the benefits for a patient outweigh the risk of taking one of these drugs. But he says this underscores why doctors should only use antibiotics when antibiotics are needed.