Use of Common Drug To Treat Malaria Could Be Cause of Antibiotic Resistance, Study Finds

Treating malaria with the low-cost, widely used drug chloroquine could increase the risk of resistance to the class of antibiotics known as fluoroquinolones, according to a study published Wednesday in PLoS One, Reuters reports.

For the study, researchers from the Lakeridge Health Centre in Oshawa, Ontario, traveled to remote rainforest regions of Guyana between 2002 and 2005 for humanitarian medical visits. Researcher Michael Silverman said the population had never been exposed to fluoroquinolones and therefore represented a unique population to study antibiotic resistance, which is thought to be linked with the overuse of the drugs. Silverman said he did not expect to find any resistance (Steenhuysen, Reuters, 7/15).

The researchers took rectal swabs from more than 500 villagers and analyzed whether bacteria in the samples, including E. coli and salmonella, were resistant to ciprofloxacin, one of the most commonly used antibiotics worldwide. The study found that more than 5% of the swabs had ciprofloxacin-resistant E.coli, compared with 4% in U.S. intensive care units, where the drug is commonly used (BBC News, 7/16). Tests of local water samples confirmed that no antibacterial agents were found in the drinking water but that chloroquine was present (Reuters, 7/15). According to the researchers, the degree of resistance was so high that it was likely that other antibiotics in the same "family" as ciprofloxacin also would have been affected (BBC News, 7/16).

The researchers then combined the drug with bacteria in the lab to confirm that chloroquine could cause drug resistance. The drug had a weak antibiotic effect that was not high enough to kill the bacteria but enough to develop resistance, the researchers found. Silverman said resistance to ciprofloxacin could extend to newer drugs in the class, such as Johnson & Johnson's Levaquin and Bayer's Avelox. "We tested for Cipro because that is still the most widely used, but we know any bacteria that is resistant to one is resistant to all," Silverman said.

The findings could have implications for artemisinin-based combination therapies, Silverman said (Reuters, 7/15). He added that the resistance "means that chloroquine use for malaria may make the fluoroquinolones less effective for many common tropical diseases, such as typhoid fever, diarrheal illnesses and possibly also tuberculosis and pneumonia in the developing world." Silverman said, "Together, these data suggest that we must focus our efforts on prevention of malaria using mosquito-control measures such as [insecticide-treated nets] and by developing vaccines," adding, "For the short term, however, we still will have no choice but to use these lifesaving antimalarial drugs."

Professor Laura Piddock, an antibiotic resistance researcher at the University of Birmingham, said that the study is "intriguing" but that it does not prove that the presence of the resistant strains was caused directly by the antimalarial drug. "These antimalarials have been co-administered with antibiotics for many, many years, and I would have expected that something like this would have been seen before," Piddock said (BBC News, 7/16).


The study is available online.