A 'Curious Orthodoxy'

A new paper published in PNAS suggests that "we're probably treating infectious disease the wrong way," says In the Pipeline's Derek Lowe. The practice of using drugs to clear all pathogens from a patient as quickly as possible, or doctors telling their patients to finish a course of antibiotics long after they feel better, "necessarily confers the strongest possible evolutionary advantage on the very pathogens that cause drugs to fail," the authors write. In other words, Lowe adds, "The harder you hit a population of infectious disease organisms, the harder you're selecting for resistance." Because of the genetic diversity present in the bacterial communities inside human patients, the hardest to kill bacteria are kept at bay by the majority, which are vulnerable to treatment. If all those are killed off, the treatment-resistant minority can take over as they have no more competition. "You want to cure the individual patient, and you want to keep their disease from spreading, and you want to keep from encouraging resistance among the infectious organisms. Optimizing for all three at once is probably not possible," Lowe says. Unfortunately, there are probably no rules that can be recommended to work in every case. "There will be circumstances when overwhelming chemical force retards evolution and other times when it drives things very rapidly. We contend that for no infectious disease do we have sufficient theory and empiricism to determine which outcome is more important," the paper's authors write. Maybe, Lowe says, the trick is to use whatever strategy minimizes resistance to treatment in individual patients.