MICRO: Antimicrobials 2 Flashcards
What are the main types of misuse of antibiotics?
- No infection present
- Selection of incorrect drug
- Inadequate or excessive dose
- Inappropriate duration of therapy
- Expensive agent used when cheaper is available
Which patients most benefit from antibiotics? What about bacteraemia?
- About 50% of people with bacteraemia would get better by themselves
- Patients who are hypotensive tend to do quite badly and mortality is higher- these patients need antibiotics quickly
What is the % of patients who get adverse events with antibiotics?
- About 5% of hospitalised people who are given an antimicrobial will experience an adverse event
What is the most common SE of antimicrobials?
GI upset/diarrhoea
NB: about 60% of diarrhoea post-antibiotics is due to SE and not C. diff.
What are the common adverse events with antibiotics?
- GI upset (i.e. diarrhoea)- MOST COMMON
- Fever and rash
- Renal dysfunction
- Acute anaphylaxis
- Liver dysfunction (abnormal LFTs seen), Hepatitis
Benefits should outweigh the risks
Where has antibiotic prescribing been most reduced in healthcare?
GP and dentists
What 4 factors should be considered when prescribing antibiotics?
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Choice of the correct antimicrobial depends on the CHAOS:
- Host characteristics (e.g. age, pregnancy, renal/ liver failure, other medications, tetracyclines deposit in bone so cannot be used in children
- Antimicrobial susceptibilities (local policies)
- Organism itself
- Site of infection (e.g. bone, CSF, urine)
Why can giving narrow spectrum antibiotics be challenging? Why is it important?
Easier to give narrow spectrum if you have sensitivities/culture but this is not commonly done
Use narrow sprectrum + bactericidal if possible e.g. penicillin for tonsillitis
What 3 pharmacological factors should be considered when prescribing antibiotics?
- Pharmacokinetics (absorption, distribution, elimination)
- Route of administration - IV for serious infection or if the patient is not absorbing PO
- Dosage (age, renal/ hepatic function, drug monitoring)
When should you consider IV over PO antibiotics?
- Sepsis - BP is low, hence perfusion is low and subsequent drug absorption PO may be compromised
- If accessing a deep site (e.g. endocarditis, osteomyelitis) or CNS (only a small proportion get into the CNS effectively)
- If antimicrobial is not absorbed well orally e.g. aminoglycosides
Name 2 methods for susceptibility testing.
- Gradient MIC method
- Agar disc diffusion method
Define MIC and break point.
MIC (minimum inhibitory concentration) = this is the least amount of drug required to inhibit the growth of the organism in a culture
Break point = the point above the MIC that determines whether the organism is sensitive or resistant to the antimicrobial
Describe the agar disc diffusion method for measuring MIC.
- The disc is impregnated with antibiotic (which diffuses out from the disc)
- Distance from the disc ↑ = conc of antibiotic ↓logarithmically
- The border of the clear zone is the MIC
- The zone of inhibited antibiotic is measured and compared to guidance (as below) and reported as sensitive or resistant.
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What is the difference between empirical and definitive treatments?
EMPIRICAL THERAPY: If it is necessary to treat the patient on an empirical basis, a broad-spectrum agent that is likely to ‘cover’ the most likely organism is used. Collect specimen before starting antibiotic
DEFINITIVE THERAPY: Empirical cover can be then changed based on culture results
How are break points determined?
Susceptibility is set by standard bodies e.g. European Committee on Antimicrobial Susceptibility Testing
reported as a table which gives breakpoints i.e. if MIC is greater than the breakpoint then it will be resistant. If the MIC is 8 and the breakpoint is less than or = to 8 then it will still be intermediate or sensitive.
What are the advantages of empirical therapy in nosocomial infections?
- higher survival rates
- shorter hospital stays
- lower healthcare costs
(nosocomial = hospital)
What are the only clnical situations where empirical therapy has been shown to improve survival?
Septic shock (e.g. hypotension) is a particularly important indication for broad-spectrum antibiotics
Patient age, bacteraemia, neutropenia, causative organism and source of infection are not associated with better outcome with empirical treatment at infection onset in this study.