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Antibiotic resistance is an emerging threat to public health. If the arsenal of effective antibiotics dwindles, treating infection becomes more difficult. Conventional wisdom has long held that stopping a course of antibiotics early may be a major cause of antibiotic resistance. But is this really supported by the evidence?

According to a new study in the BMJ, the answer is no.

The notion that a longer course of antibiotics prevents resistance started early in the antibiotic era, when doctors found that patients with staphylococcal blood infections and tuberculosis relapsed after short antibiotic courses. Today, we know that patients with bloodstream infections may require several weeks of antibiotics for cure, and those with active tuberculosis need many months of multiple antibiotics. But these patients are not representative of most people who receive antibiotics today.

In fact, the optimal length of treatment in many common infections is not well studied and may be more than a little arbitrary. One infectious diseases doctor has suggested, somewhat satirically, that most of our current rules for antibiotic administration have more to do with the number of days in the week than they do with robust scientific evidence.

The authors of the BMJ study reviewed the data on length of therapy in several common infections, such as strep throat, cellulitis (skin and soft tissue infections), and pneumonia. In most conditions, shorter courses of therapy resulted in cure rates that were the same as longer durations of antibiotics. There was one notable exception: children with middle ear infections (otitis media) had higher cure rates with ten days of antibiotics, compared to five days.

In a few of the studies, researchers looked at the risk of having antibiotic-resistant bacteria on the body after antibiotic therapy. Compared to those who received longer courses of antibiotics, patients who received fewer antibiotics had either the same or a slightly lower risk of being colonized by antibiotic-resistant bacteria.

Better ways to know whether antibiotics are needed at all

Doctors are studying new clinical tools to help limit unnecessary antibiotic use. One of these is a blood test called procalcitonin. Levels of procalcitonin rise in patients with serious bacterial infections. In patients with viral infections, which do not respond to antibiotics, procalcitonin levels are suppressed. Currently, procalcitonin levels are used in the hospital setting to help decide whether patients with flares of COPD (chronic obstructive pulmonary disease) or pneumonia are likely to need antibiotics or not. Procalcitonin might also be useful as a test to determine whether primary care patients need antibiotics, but it hasn’t yet been well studied in the office setting.

Although many infections may do well with minimal or no use of antibiotics, some serious infections definitely require long-term antibiotics. This is especially true of infections that lead to hospitalizations, such as bloodstream and bone infections.

Here’s the bottom line