Category Archives: Antimicrobial Stewardship

“Carbapenem Conundrums”

Antimicrobial Resistance, Antimicrobial Stewardship, The Science of Microbiology,

Last week, while on-call I recommended a carbapenem for three different patients within the space of 30 minutes. Yes, it happens sometimes! Most empiric antibiotic choices do not require the inclusion of a carbapenem, but key factors to consider are ESBL history, travel or hospitalisation in areas with high ESBL endemicity, and how sick the patient is.

It is interesting to look at the psychology of carbapenem prescribing. Some doctors prescribe carbapenems because they are afraid of giving treatment to their patients that might not cover all resistance profiles. Others are afraid of prescribing carbapenems because they are traditionally the top line treatment and scared of criticism from antimicrobial stewards like myself!

But if you have to use a carbapenem, which one should you use?

The main choice in New Zealand is generally between meropenem and ertapenem. Imipenem-cilastatin is rarely used now in New Zealand, mainly due to its seizure risk. (There is a little evidence that it is the optimal carbapenem for disseminated nocardiosis and a few other isoteric indications) Other carbapenems outside these three have limited availability in NZ hospitals, or at least the ones I work in. This may be different elsewhere in the world.

Choosing between meropenem and ertapenem:

Here are most of the key factors I take into account when choosing between the two

Organism coverage-If I need to empirically cover Pseudomonas or Enterococci or Acinetobacter spp., then meropenem is a better option than ertapenem due to its broader coverage.

CNS penetration-Meropenem is a better option than ertapenem due to better CNS penetration. I had a patient with E.coli meningitis recently who required meropenem until the susceptibilities were known.

Hypo-albuminaemia– Ertapenem is highly protein bound compared to meropenem, so in hypo-albuminaemic states, the free fraction of ertapenem is increased, and it is chucked out through the kidneys leading to a decreased half-life. Therefore, meropenem is preferred in hypo-albuminemia. I use 25 g/l as an arbitrary cut-off.

Dosing frequency– If reduced dosing frequency is preferred due to patient compliance/outpatient therapy etc, then once daily ertapenem is preferable to three times a day meropenem.

Penetration into biliary tissue-Ertapenem has poor penetration into biliary tissue compared to meropenem, so I prefer meropenem for biliary infections.

Duration of treatment- Meropenem is more stable than ertapenem against resistance mechanisms such as upregulation of efflux pumps or porin channel loss. These mechanisms can become an issue with prolonged treatment and should be taken into account when choosing between the two.

Although the above points might suggest otherwise, I actually recommend more ertapenem than meropenem. Ertapenem is absolutely fine for most straightforward cases of urosepsis where empiric ESBL coverage is required.

One other point. If you do need to utilise a carbapenem, then regular review and timely de-escalation based on the patient’s condition and/or susceptibility results is important to optimise antimicrobial stewardship.

Michael

“Reporting susceptibilities on UTIs, not urinary isolates…”

Antimicrobial Resistance, Antimicrobial Stewardship, , , ,

Urines arrive at diagnostic microbiology laboratories in considerable numbers. My own lab in New Zealand processes a couple of thousand urines a week. A significant proportion of these will have positive cultures. Therefore, the potential for the laboratory to promote good antimicrobial stewardship with respect to urinary tract infection is considerable.

My mantra on this is as follows: “The microbiology lab should never release antibiotic susceptibilities on a positive culture from a urine sample unless there is reasonable evidence accompanying the request that the patient has a UTI.”

The fact that the urine sample has turned up at the microbiology lab is insufficient evidence per se that the patient has a UTI. Urines get sent to microbiology laboratories for all sorts of spurious reasons, see below for a few examples:

  • Urines often get sent “automatically” from acute receiving wards as part of a blanket laboratory screen, where the patient may have a diverse spectrum of symptoms such as chest pain, shortness of breath, collapse, etc.
  • Urines can get sent from Long Term Care Facilities when someone decides to dipstick all their patients and send the urine samples with positive dipsticks to the lab for culture. Yes, it happens, and a lot more often than you might think!
  • Urine from indwelling catheters can get sent when the patient has a blocked catheter, or the catheter bag is cloudy.
  • Urines from patients attending outpatient clinics should also raise a flag. With the exception of urology clinics, patients who attend a pre-planned elective clinic appointment generally do not have an acute UTI. The same principle can apply for patients who are in hospital wards for other reasons.
  • Urines where the clinicians are looking for other tests, i.e. albumin/creatinine ratio, and due to laboratory processes the urine ends up getting cultured as well…

So, my argument is that if a urine sample turns up at the laboratory without any clinical details or with inappropriate clinical details, the lab is under no obligation whatsoever to release antibiotic susceptibilities on any organisms grown. 

The best approach of course is not to process the sample at all unless relevant clinical details are received. I would regard all of the following clinical details as being unacceptable to justify proceeding to urine culture:

  • No clinical details
  • Cloudy urine
  • Concentrated urine
  • Dark urine
  • Smelly urine
  • Urine dipstick urinalysis results only
  • Routine/monitoring/screening urine
  • Fatigue
  • Increased CRP
  • Lots of other non-specific symptoms!

The easy option for the lab of course is just to accept the sample, report the organisms, and the accompanying susceptibilities. However, this is almost certainly not the best way…

Michael

“Antimicrobial Stewardship and the Problem of Unsolicited Advice”

Antimicrobial Stewardship, The Art of Microbiology,

“I would stop that fluoroquinolone…”

A good proportion of my job as a clinical microbiologist is being an antimicrobial steward. i.e. giving antibiotic advice based on microbiology results. And a good chunk of this advice is “unsolicited”, in that nobody has specifically asked for it. One could argue that the advice is “semi-solicited” in that it is given under the auspices or framework of an Antimicrobial Stewardship Program.

Being on-call over the Christmas period has made me reflect on the difference between giving solicited and unsolicited antibiotic advice. When someone specifically asks for your advice, they are genuinely interested in what you have to say and for the most part listen and act on your recommendations. However, when the advice is unsolicited, regardless of whether it is given by phone or in-person, it may not always be welcomed with open arms…

It is not that the prescriber necessarily disagrees with your advice. They know it is generally correct in purist terms. It is just that there are (several) other agendas at play for the attending clinician.

Taking it from the clinician’s perspective, antibiotic advice from an antimicrobial steward on occasion may prevent early discharge and may create logistical issues in terms of organising outpatient antibiotics, arranging further investigations, or arranging clinic follow-up. Put in simpler terms, more work. Such factors are accentuated during the Christmas break where the (laser) focus is on getting patients out of hospital, and minimising any admin work that is required during the holiday season.

A classical example of this is advising on a Staphylococcus aureus bacteraemia. (2 weeks IV abx, Echocardiogram, repeat blood cultures, etc.) Sometimes the attending clinician just doesn’t want to know…

Of course, sometimes our advice can be beneficial to the patient workflow & pathway. For example, early oral switches, and promotion of short course antibiotic therapy. I think it is really important to focus on documenting & highlighting such “wins”, as a counterbalance for when “bad news” needs to be given.

Personally, I am a little fatalistic when it comes to whether my advice is accepted, whether it solicited or unsolicited. I believe in the principle that the final management decision always rests with the attending clinician and they can choose whether to take my advice or not. There is only so much that you can do…

Building up relationships and trust is key in getting people to listen to your unsolicited advice. Some prescribers are more receptive than others. And some specialties are more receptive than others.

So, is unsolicited advice more about the giver than the receiver? Is it essentially self-serving in nature? Or is it a necessary evil of being a good antimicrobial steward? These are difficult questions, and ones that I do not have the answers for.

The other approach is to have a more passive approach to antimicrobial stewardship, to only give advice when it is specifically asked for, or at least to issue clear guidelines as to when advice should be sought.

My children often complain when I give them unsolicited advice on how to live their lives. I hope that my clinician colleagues do not feel the same way!

Michael

Check out this interesting article on the psychology of antimicrobial stewardship, published in CID