Principles of antimicrobial use Flashcards
What are the main steps of the systemic approach to antimicrobial use?
- Confirm presence of infection
- Identification of pathogens
- Selection of antimicrobial and regimen
- Monitor response
How to confirm presence of infection and indication for antibiotics?
- Risk factors
- Subjective evidence
- Objective evidence
- Possible site of infection
What are some host factors to consider when choosing a regimen for the patient?
Age, Hx of allergies and ADR, Pregnancy and lactation, renal/hepatic impairment, status of host immune function, severity of illness, recent antimicrobial use, healthcare-associated risk factors
Organism factors to consider when choosing a treatment regimen:
Identity of infecting organism, susceptibility of infecting organism
Benefits of combination therapy:
- Extend spectrum of activity
- Synergistic bactericidal effect
- Prevent resistance
Disadvantages of combination therapy:
- Increase risk of toxicity and allergy
- Increased chances of DDI
- Increased cost
- Selection of MDR bacteria
- Superinfections
- Antagonistic effects
Drug factors to consider when choosing a treatment regimen:
- Spectrum of activity
- Ability to reach site of infection
- PK-PD
- Route of administration
- Side effects/ADR
- DDI
- Drug cost
What has to be focused on when monitoring the response to treatment?
- Treatment goals
- Therapeutic response
- ADR
- When susceptibility/microbiological tests are available, optimise therapy
- Satisfactory response
- Unsatisfactory response may be due to :
- Inappropriate diagnosis, inappropriate choice of agent, subtheraprutic conc, Collections/abscess, impaired host defences, superinfection and toxicity of drug
What is the objective of the ASP?
- Best clinical outcomes
- Minimise toxicity and other adverse events
- Limit selective pressure on emergence of antimicrobial-resistant strains
- Decrease excessive costs attributable to suboptimal antimicrobial use
What are some of the antibiotics that require conc-dept bacterial killing?
- Aminoglycosides
- Fluoroquinolones
What are the antibiotics that are time dependent with no persistent effect?
- Penicillins
- Cephalosporins
- Carbapenems
Which antibiotic is time dependent with persistent effects?
- Vancomycin
Procalcitonin levels that encourages the starting of antibiotics
≥0.5µg/L
- ≥0.5, < 1µg/L: encouraged
- ≥ 1µg/L: strongly encouraged
Procalcitonin levels that encourages the stoppping of antibiotics
- <0.25µg/L: stopping strongly encouraged
- Decreased by 80% from peak conc. or ≥0.25, < 0.5 µg/L: stopping encouraged
A patient has CRP = 39mg/L. Does this confirm the presence of infection?
No. CRP increases whenever there is inflammation
Usual CRP levels for bacterial infection is very high (>40, can go above 200mg/L)
Pathogen vs colonisers vs contaminants
- Pathogen: cause true infection, can damage tissue and elicit host response
- Colonisers: presence of normal flora/organisms
- Contaminants: Acquired during collection/processing host specimens w/o evidence of host response
Likely contaminant from blood culture
S.epidermidis, bacillus
Likely coloniser from urine culture
Yeast
The three principles of antimicrobial selection to achieve improved patient outcomes
- Timely initiation of most effective, least toxic and narrowest spectrum agent
- Individualised dosage appropriate to organism and site of infection
- Timely and appropriate alteration to clinical response, and use shortest duration possible
Abx that are generally avoided in children
- FQ (fear of arthropathy)
2. Tetracyclines (permanent teeth discolouration)
Abx avoided in G6PD patients
Sulfonamides, Nitrofurantonin
Abx which are generally safe in pregnancy
Macrolides, B-lactams
Distributes well to prostate hence are drugs of choice for prostatitis
Ciprofloxacin, co-trimoxazole
The dosing strategy for drugs exhibiting concentration-dependent bacterial killing
Larger doses at extended intervals (e.g. OD AG)
The dosing strategy for drugs exhibiting time-dependent bacterial killing with no persistent effect
More frequent dosage administration, and continuous IV where needed.
May add another drug to block excretion of the Abx (e.g. probenacid increase half-life of penicillin)
The dosing strategy for drugs exhibiting time-dependent bacterial killing with persistent effect
- Optimise AUC/MIC ratio, dependent on total daily dose
- Consider convenience when administering
(E.g. though vancomycin 500g q12h or 1g q24h has same killing effect, use q24h since it is more convenient)
A patient on nasogastric tube presents with mild infection and is prescribed antibiotics. What is the preferred route of administration for the Abx?
Oral route (via the nasogastric tube) unless unavailable
A patient is on IV Abx and is now feeling much better. She is afebrile and able to swallow. Her culture results are also available.
What are the appropriate modifications to her treatment plan?
- Convert IV to PO
- Streamline Abx
- Stop if adequate duration of Abx has already been given
What are some therapeutic response to look out for after administering Abx?
- Resolution of Sx and signs
- Microbiological clearance (eradication of organism)
- Absence of complications and progressions
After administering Abx, when should clinical response be evaluated before deciding to modify the therapy?
48 - 72 hours
Abx usually take time to work
What does “MINDME” stand for in being an antimicrobial steward?
- Microbio guides therapy wherever possible
- Indications should be evidence based
- Narrowest spectrum
- Dose appropriately to site and type of infection
- Minimise duration
- Ensure Monotherapy
What is Post Antibiotic Effect (PAE)?
Ability of an antimicrobial agent to persistently suppress bacterial growth even at low or undetectable concentration.
This can also help prevent adaptive resistants as the low concentration prevents microbes from adapting to the Abx, hence prevents selection of more resistant mutants
