Tag Archives: antibiotic duration

“How long is a piece of string?”


A question that often ‘scunners’ me is “What should the duration of the antibiotic course be for this patient?”

Let me get out my crystal ball…

It is a question I get at least once a day.

And my heart tends to sink a little on hearing it…

I have no problem (and quite enjoy) guiding the clinician to the right antibiotic, but I find this particular question on duration very hard to answer with any degree of personal conviction.

I usually give one of the ‘magical’ and hallowed numbers such as 3, 5, 7, 10 or (god forbid) 14,  usually along with a sizeable disclaimer saying that for the most part, antibiotic duration is very much an arbitrary and non-scientific decision.

Sure, for the more critical infections such as endocarditis, osteomyelitis and prosthetic joint infection there are guidelines on antibiotic duration which I try to adhere to, but even then there is not a lot of evidence to back these durations up, and such guidelines tend to compress all patients into the one category…

And for hospitalised patients with infections that don’t fall well into any particular guideline, my response is often along the lines of “Until they are better”, “As long as it takes” or even “How long is a piece of string?”

I suspect 95% of antibiotic courses are longer than they need to be, and this may well have undesirable effects, and not just on the patient themselves. I am a strong advocate of putting mandatory limits on the duration of antibiotic that can be prescribed in “one go” by the prescriber without clinical review. For me it is a key element of anti-microbial stewardship.


Check out this related article on antibiotic duration…


Old Wives Tales: Antibiotic Duration and its Effect on Antibiotic Resistance

As a child you may remember being told by your doctor to finish your course of antibiotics so that the bug does not become resistant…. I think such a myth still exists today, possibly to a somewhat lesser extent. In reality, a longer than necessary course of antibiotics just prolongs the selection pressure for resistant organisms to thrive and thus leads to antibiotic resistance. 

In fit healthy people, antibiotic courses for straightforward UTIs, URTIs, simple soft tissue infections etc., can often be remarkably short (if antibiotics are needed at all), and people may notice a significant improvement in their symptoms after just one or two doses.

It is also important to note that the patient’s immune system usually works in tandem with antibiotic therapy so when the pathogenic bacterial load has been reduced by the first few doses of antibiotics it makes it easier for a patient’s immune system to complete the job of controlling the infection.

The real message to get across here is that antibiotic courses should be of sufficient duration to deal with the infection but not so prolonged that it unnecessarily promotes selection of resistant bacterial strains.

For most antibiotic courses, the maximal effect usually occurs after the first couple of doses and then any further effect tails off very quickly after this. I occasionally come across patients both in the hospital and community setting where the patient has been on the same antibiotic for weeks if not months to treat a particular infection. Only very rarely is this indicated, and in my opinion should never be done without consultation with a specialist.