1s: Antimicrobials 2 Flashcards
Give examples of antibiotic misuse
- no infection present
- inaequate/excessive dose
- selection of incorrect drug
- inappropriate drug therapy
- expensive agent used when cheaper is available
CHAOS = things to consider when prescribing antimicrobials
- C - choice of correct antimicrobial depends upon the…
- H - host characteristics (i.e. renal failure, pregnancy, allergy, age, genetics, hepatic function)
- A - antimicrobial susceptibilities of the…
- O - organism itself and also the…
- S - site of infection (i.e. bone, CSF, urine)
Guidelines for choice of drug
- use NARROW spectrum if possible
- use BACTERICIDAL drugs if possible
- ideally, choice based on bacteriological diagnosis (or best guess based on DDX)
- consider local sensitivity patterns
- patient characteristics
- cost
Other factors to consider:
- pharmacokinetics (absorption, distribution, elimination)
- route of administration (e.g. sepsis → low BP → perfusion of intestines low → oral drug absorption compromised.)
- IV recommended if = infection is serious, deep infection, patient not absorbing orally, treat CNS infection
- dosage (age, renal/hepatic function, drug monitoring)
What is MIC?
Minimum inhibitory concentration
- minimum drug concentration needed to inhibit growth of organism in a culture
- guidelines = if MIC is higher than X, the organism is resistant
Agar Disc Diffusion Method
- Time-consuming
- The disc is impregnated with abx which diffuses out from the disc
- as distance from disc increases, concentration of abx decreases logarithmically
- the border of the clear zone is the MIC
Empirical therapy
- It is important to collect specimens for culture BEFORE starting empirical antibiotic therapy if possible
- Empirical cover can then be changed based on the culture results
- Empirical therapy covers the most likely organism (even before you know the exact one)
In patients with nosocomial infections, appropriate initial ABx is associated with higher survival rates
- So, broad spectrum ABx are an optimal initial choice for nosocomial pneumonia and severe sepsis
- Septic shock is a particularly important indication for broad-spectrum antibiotics
Identification of organisms ix
- Gram-staining (send as much specimen as possible higher volume of sample means higher sensitivity)
- Rapid antigen detection
- Immunofluorescence
- PCR
Site of infection factors
Local concentration of the antimicrobial will be affected by factors such as:
- pH at the infection site
- Lipid-solubility of the drug
- Ability to penetrate the blood-brain barrier
Special considerations are needed for endocarditis and osteomyelitis
Need for antimicrobials: check for evidence of a systemic response, route of administration
- IV to PO switch is recommended in hospital for most infections if the patient has stabilised after 48 hours of IV treatment
- In CNS infections and severe infections such as osteomyelitis and endocarditis you may NOT switch to PO
PK/PD predictors of efficacy
3 patterns of antimicrobial activity: type 1
Peak above MIC (Cmax) is the MOST IMPORTANT FACTOR (as concentration-dependent effects)
→ aminoglycosides given as one big dose a day to get max Cmax
however, adverse effects (ototoxicity and nephrotoxicity)
- also measure trough concentrations to ensure drug is being eliminated
- accumulation of drug is associated with toxicity
→ PEAK influence dose of drug give, TROUGH, determines frequency
- NOTE: if a patient has renal failure than you may be worried about giving a full dose of aminoglycosides however, if their renal failure is caused by the sepsis then you would want to start off with the full dose and worry about the nephrotoxicity and accumulation later
3 patterns of antimicrobial activity: type 2
Type II (e.g. Penicillins)
- These are time-dependent, so you want to maximise the time above the MIC
- The concentration above the MIC is NOT very important
- So, with penicillins, you tend to take them quite frequently (3-4 times per week)
3 patterns of antimicrobial activity: type 2
Type II (e.g. Penicillins)
- These are time-dependent, so you want to maximise the time above the MIC
- The concentration above the MIC is NOT very important
- So, with penicillins, you tend to take them quite frequently (3-4 times per week)
3 patterns of antimicrobial activity: type 3
Type III (e.g. Vancomycin)
- Sort of a combination of Type I and Type II
- The AUC above the MIC is the MOST IMPORTANT factor (both concentration and time-dependent effects)
- Infusions can maintain an AUC above the MIC
Length of treatment decision
Length of treatment decision
UTIs
C. diff colitis
