Stewardship Flashcards
What can we do to improve/reduce antimicrobial use in animals?
- Use antimicrobials less often
- Use lower priority drugs when possible
- Dose them properly
- Optimize durations
is longer course of antibiotics always better?
no, pretty much all studies have found that short course is equally effective
> watch out for dogma
Common conception: IV antibiotics are required for many serious infections.
-Truth?
- Antimicrobial efficacy is dependent on the drug concentration at the site of infection
- If a drug is bioavailable orally, has established oral dosing regimens and is administered successfully, and there are no patient factors that would inhibit drug absorption, does route matter??
where did idea that IV is better for serious infections come from?
- Humans, osteomyelitis
- Waldvogel et al (1970) reported IV penicillin or aminoglycosides, with no oral
treatment - Concluded “…osteomyelitis is rarely controlled without the combination of
careful, complete surgical debridement and prolonged (4 to 6 weeks)
parenteral antibiotic therapy at high dosage” - Paper has traditionally been cited as indicating IV treatment is needed
- Endocarditis
- Multiple studies in the 1940s/1950s showed oral sulfanilamide, erythromycin
or tetracycline were inferior to IV penicillin - Finland et al 1954 review article: “Presumably, the oral route is at times
successful…it is more likely, however, that such usage is responsible for many therapeutic failures….However, little of this type of experience is recorded, and therefore this assumption cannot be authenticated” - But, were differences because of ROUTE or DRUG?
- Sulfa,oralerythromycinandtetracyclinearepooroptionsfortypicalhuman
endocarditis because of low peak blood drug levels cases while penicillin is (was) an excellent option
- “If you start and antimicrobial, you have to use it for X days to avoid development of resistance”
- truth?
- Each dose of an antimicrobial will inhibit susceptible organisms and select for resistant organisms.
- More doses = more selection pressure.
- I’m not aware of any data, in any species, that show longer courses of antibiotics result in less resistance, or that clinical relapses lead to resistance
- I can’t think of any pathophysiology for increased resistance risk with less treatment
- Inadequate treatment duration could impact treatment efficacy, not likelihood of resistance emergence.
- When it’s determined there’s no clinical need for an antimicrobial, it should be stopped
“I took over a case this morning and it’s on ampicillin, clindamycin, enrofloxacin, doxycycline and metronidazole. Do we need all those drugs?”
- what do we do?
De-escalation
* Reconsideration of empirical therapy
> After case has progressed
> When lab results are available
* Regular review of the antimicrobial regimen
* Consideration of transition of inpatients to outpatient-amenable treatment
“Bactericidal antibiotics should be used for serious infections, immunocompromised patients, or immune priveleged sites”
-truth?
- Classic assumption:
- Bactericidal drugs kill while bacteriostatic drugs inhibit growth
- Bactericidal definition:
- Drugs where the in vitro minimum bactericidal concentration (MBC) is <= 4X
the MIC and a 99.9% reduction of bacterial concentration is achieved after growth in vitro for 18-24h - But…bacteriostatic and bactericidal are
- In vitro properties
- Somewhat arbitrarily defined
- Impacted by bacterial inoculum, growth conditions, growth phase, local site
physiologic properties… - Not black-and-white:
- Some ‘bacteriostatic’ drugs are bactericidal for certain bacteria or in some situations * Some ‘bactericidal’ drugs do not hit that MBC:MIC ratio at the site of infection
- A drug could kill 99.99% of bacteria in vitro at a different inoculum concentration or time than the arbitrary and be classified as bacteriostatic
- A bactericidal drug could kill <99.9% of bacteria with higher inocula or different conditions
- Review of 56 trials since 1985
- 49 reported no difference between cidal and static drugs * 6 reported superiority of bacteriostatic drugs
- 1 reported superiority of bactericidal drugs
> But…static drug was underdosed based on retrospective PK/PDanalysis - “It is time to abandon the notion that bactericidal antibiotic agents are
intrinsically more effective than bacteriostatic agents” * Pick the best drug…ignore cidal vs static
human data for static vs cidal drugs?
- No demonstrated significant clinical benefit of bactericidal drugs for:
- Immunocompromised hosts
- Immune privileged sites
- Severe disease (e.g. sepsis)
- Some bacteriostatic drugs are recommended first line treatment for serious infections (e.g. linezolid for bacterial endocarditis, McDonald 2023)
- Good study for endocarditis and meningitis is lacking
- Pick the best drug…ignore cidal vs static
Bacteriostatic effects (decreasing growth) inhibit bactericidal effects (that typically occur during growth)
-is this true? should we not combine cidal and static drugs?
- not necessarily, but can be an ok rule of thumb…
Culture and Susceptibility Testing pros and cons
Pros
* Targeted antimicrobial treatment
* Confirmation of disease
* Better interpretation if treatment fails
Cons
* $$
* Time delay
* Misleading results with improper sampling, lab methods, contamination…
> A properly collected sample is rarely contraindicated, but it’s not always indicated
- 3 yr old indoor/outdoor cat
- Presented for facial swelling of at least a few days’ duration
- Quiet, poor appetite
- Fever
- Pain over neck
- What is the disease process? * Where is the infection?
- What do you do?
- Incision and drainage
- Antibiotics for tissue infection *
Likely pathogens - Pasteurella, Staph, Strep, Enterobacterales
- Easy to penetrate tissue sites (outside the abscess)
- Cat moderately amenable to treatment
- Amoxicillin/clavulanic acid: 3-5d
Would you culture…..
* 5yr old dog with first episode of cystitis?
probably not, asl client
Would you culture…..
* 5 yr old dog with first episode of cystitis but a history of recurrent
superficial folliculitis?
more useful to have a culture
Would you culture…..
* 5 yr old dog with first episode of cystitis whose owner is frequently
hospitalized?
push to culture this
Would you culture…..
* 3 yr old cat with first episode of cystitis?
yes - very low probability it is bacterial
