According to the studies, the optimal use of the drugs might slow the spread of drug resistance while making the patient just as healthy. Andrew Read, professor of biology at Penn State, and an associate at the Center for Infectious Disease Dynamics said that normally in the absence of drugs, the susceptible pathogens keep the resistant ones from proliferating. But when infections are treated with drugs, the dynamic changes.
"Drugs kill off the susceptible parasites letting their competitors, the resistant ones, fill the vacant space and expand their numbers," Read said.
The study was conducted on mice infected with malaria to see how the parasites respond to drug treatment. Researchers found that once the drugs eliminated the susceptible microbes, the number of resistant bugs increased twice as much, compared to when the susceptible microbes were present, or when the infections comprised only resistant bugs.
"The more drugs you use, the worse you make the situation in terms of the evolution of drug resistance. This massively increases the rate of spread of resistance, so the drugs become less and less useful," he added.
The increase in parasite numbers was found to be directly proportionate to the duration of drug treatment. "Resistant parasites not only survive but do much better because the drugs have successfully removed their competitors," Read explained.
"We suspect this is what is causing the short lifespan of many antimalarial drugs," he added. If the infections in mice mirror malarial infections in humans, the findings may offer a promising solution in slowing the spread of such drug resistance.
The research team also included Andrew R. Wargo, now a post-doctoral researcher at the University of Washington, Seattle, Jacobus C. de Roode, now an assistant professor at Emory University, and Silvie Huijben and James Shephard, doctoral student and undergraduate student respectively at the University of Edinburgh.
The findings appear online in the Proceedings of the National Academy of Sciences.