Studies presented at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy, sponsored by the American Society for Microbiology, suggest that calcium-fortified foods may hinder the effectiveness of antibiotics, according to a report by United Press International.
Guy Amsden, a clinical pharmacy specialist at Bassett Healthcare in Cooperstown, New York, described how blood levels of the new fluoroquinolone antibiotics - gatifloxacin and levofloxacin - were reduced when healthy volunteers took the medication with calcium-fortified orange juice.
"People may be doing exactly what their doctors recommend and may not be getting benefit of the drugs," Amsden told UPI.
He said there was a 14 per cent reduction in gatifloxacin levels and a 16 per cent drop in levels of levofloxacin. Previous studies showed even greater reductions with ciprofloxacin. According to Amsden, fluoroquinolones are the preferred treatment for patients suffering from community-acquired lung infections.
"We now suggest that doctors tell their patients: 'Take these quinolone antibiotics on an empty stomach', in order to minimise these reactions," he said.
Amsden suggested that failure to take into account these interactions might in the long-term lead to higher costs because patients might need to take medicines for a longer time. There also might be adverse side effects associated with protracted courses of treatment, development of resistant microbes and need for hospitalisation because the patient may require intravenous delivery of antibiotics.
"Doctors now usually tell patients to avoid calcium-containing antacids, but people tend not to think of foods as mineral supplements," Amsden explained.
"It's possible that some patient with bronchitis could take these antibiotics with a breakfast cereal-based meal with juice and milk and come back to the doctor with a case of pneumonia. And the doctor would think that the patient isn't compliant in taking medication, when in fact the patient took the drugs just as the doctor ordered."
In the study on gatifloxacin, 16 healthy volunteers were given a single 400-milligram tablet of the antibiotic and also took either 12 ounces of water, 12 ounces of orange juice or 12 ounces of calcium-fortified orange juice. Amsden reported a statistically significant reduction in serum levels of gatifloxacin when the calcium-fortified orange juice consumption was compared to water. There was no significant difference between water and plain orange juice. The study on levofloxacin produced similar results, according to the report.
Amsden explained that the active components of the antibiotics get bound up with calcium in the gut and then is excreted without even finding its way into the bloodstream. He said he is performing further work in analysing how mineral-fortified cereals with milk may affect the level of antibiotic that gets into the bloodstream where it can fight infections.