Tag Archives: antibiotic reporting

“Keeping it simple or keeping it accurate…”

Let’s say you are a clinician and you are looking at two different microbiology results on two different patients (A&B). Both have an E. coli UTI. Both results state that the E. coli is susceptible to trimethoprim. However what you don’t know is that the E. coli isolate on Patient A had a trimethoprim disc diffusion zone of 18mm (right on the EUCAST breakpoint), whilst for patient B the corresponding zone was a much more comfortable 26 mm.

And who knows, if you repeated the same testing on patient A a dozen times, the chances are you would have a few “non-susceptible”results, due to the natural margin of error of the test.

If I was a clinician, and had this extra (zone diameter) information, I would be a lot happier prescribing trimethoprim to patient B, even though they both have in-vitro “susceptibility” reported on the result. (The same principle of course applies if we were talking about Minimum Inhibitory Concentration (MIC) values instead of zone diameters.)

But do clinicians really want this extra information?

They are usually very busy, …and not particularly interested in microbiology.

In my experience all clinicians generally want to know is if an isolate is susceptible or resistant. They are not particularly interested in the details, with the exception of blood culture and sterile site isolates, when there is at least a modicum of interest in the degree of susceptibility or resistance.

So which is better.. a susceptibility result full of information, but potentially difficult to understand and interpret, or a result reduced to its simplest form.

There is no right answer of course…

I am not even convinced antimicrobial susceptibility breakpoints have a long term future.

More and more, year by year, the anti-microbial susceptibility committees (EUCAST, CLSI) are trying to take into account antibiotic dose,  renal function, degree of infection, etc. when setting antimicrobial breakpoints.

But they are really only scratching the surface…

Time for some major disruption!


“The Whole Picture”

For the clinical microbiologists and ID physicians….

It might be the most susceptible antibiotic on the report but the child will only take syrup and not tablets.

It might be the most susceptible antibiotic on the report but there is little chance that this patient will take antibiotics four times a day.

It might be the most susceptible antibiotic on the report but it tastes horrible. Is this patient likely to stomach it?

It might be the most susceptible antibiotic on the report but it causes diarrhoea in a good proportion of patients. Will this patient “run” with it?

It might be the most susceptible antibiotic on the report but this patient swears by another antibiotic.

These are only a few of the things that should be considered when individualising treatment. Advising on the best antibiotic is not just about looking at the report and looking for the most susceptible antibiotic available. It is about “What antibiotic is most likely to work best in this particular patient?”. Getting good at this sort of decision making takes time and experience and a good deal of background knowledge, not all of which can be learned from textbooks. We certainly don’t always get these decisions right.



“Use it or Lose it? Listen to yourself.”

Take for example a couple of the latest antibiotics on the block, tigecycline and ceftaroline.

As new, broad spectrum anti-microbials they should be given the utmost protection in order to prevent selection of antibiotic resistance, only being used in cases where there are few or no other reasonable options available. 

The pharmaceutical companies will not tell you this however. They would like you to use the drug as much as possible, for obvious reasons.

…and sometimes general physicians will have heard of these new antibiotics and because they are new, assume they are the best, and seek to use them.

… and sometimes Clinical Microbiologists and ID physicians like to use new antibiotics like these because it makes them look clever, or in order to stay ahead of “the game”.

….and sometimes pharmacists feel the compulsion to stock a few vials of all the exotic antibiotics, just in case…

….and sometimes the CEO will want these antibiotics used in his/her hospital, because other neighbouring hospitals are using them.

….and sometimes the patient will have heard of the latest new antibiotic on the news or internet, and demand its use.

Protection of antibiotics like these starts in the laboratory, with focused testing and reporting. It always has done, always will do. If you test or report any such antibiotics on a routine basis, you need to take a long hard look at your laboratory policy.

 I have hardly ever reported or advised the use of these antibiotics, because in the area of the world I work in, there is very little need for them. I suspect this will be the case for the vast majority of us.

When we make decisions on which antibiotics to test, which to report, which to advise etc, there may be several opinions given to you, or subtle pressure applied from various sources.

Listen to the advice, be aware of the agendas, and always, always make up your own mind.