You’ve probably heard it for years, every time you get a prescription for antibiotics: “Make sure to take all the pills.”

Traditionally, clinicians have given two reasons for these strict instructions: So the infection doesn’t come back, and so you don’t end up with bugs so hearty that antibiotics can’t kill them.

But these days, clinicians like me are starting to rethink this approach.

As a physician specializing in infectious diseases and the medical director of the the University of Virginia’s antimicrobial stewardship program, I’ve spent much of my career focused on using antibiotics wisely and encouraging colleagues to be thoughtful about how they choose and for how long they prescribe these medicines.

The evidence around how long patients should take antibiotics is more nuanced than the traditional advice to “finish the course” suggests. Yes, it’s still a good idea to follow your doctor’s advice – but not because stopping your medicine early would breed bacteria that are resistant to antibiotics.

A mistaken cause of microbial resistance

When physicians began to use penicillin widely in the 1940s, they noticed something curious in the first few hundred patients. Some improved dramatically in just a few days, while others required longer courses to cure their infection and avoid relapse.

Studies eventually showed that the type of infection a patient has, the specific bacteria causing it and how well an antibiotic can penetrate into infected areas in the body all play a role in this variation.

But the message that patients must finish whatever course of antibiotics they were given – which was promoted by the Centers for Disease Control and Prevention and World Health Organization – was based on a misconception that if you don’t kill all the infecting organisms right away, the ones that come back and cause a relapsed infection will be resistant to the original antimicrobial........

© The Conversation