Doctors often tell patients to take a “course” of antibiotics, because a partially treated infection may result in relapse with antibiotic-resistant bacteria. But where does this advice come from?
As Lyn Gilbert has pointed out on The Conversation, there isn’t good evidence behind many of these recommendations. For GPs, the main determinant of the duration of antibiotics is the size of the pack they come in.
In hospitals, we also have some odd rules about antibiotics:
- Prime numbers for durations of up to a week (three, five or seven days)
- Even numbers for more serious infections that take weeks to eradicate (two, four or six weeks)
- Multiples of three for really tenacious infections such as bone infections (three months) or TB (six months).
Of course, there is nothing magical about these numbers. I doubt anyone was harmed by stopping their treatment on day 89 instead of day 90.
Although this seems rather silly, it highlights the serious point that we often don’t know exactly how long is necessary to treat many infections.
