MI: Antimicrobials 2 Flashcards
List some ways in which antibiotics can be misused.
- No infection present
- Selection of incorrect drug
- Inadequate or excessive dose
- Inappropriate use of empirical antibiotics
NOTE: about 50% of people with bacteraemia will get better by themselves
List some common adverse events associated with antibiotics.
- GI upset
- Rash and fever
- Renal dysfunction
- Acute anaphylaxis
- Hepatitis
What does the ‘CHOICE’ of correct antimicrobial depend on?
- Host characteristics (e.g. age, pregnancy)
- Antimicrobial susceptibility
- Organism
- Site of infection (e.g. bone, CSF)
NOTE: you should try to use a narrow-spectrum bactericidal drug where possible
Which types of infection typically require IV antibiotics?
- Serious infection
- Deep/CNS infections
What is MIC?
- Minimum inhibitory concentration - minimum concentration of drug required to inhibit bacterial growth
- There is a regulatory body that sets the MIC cut-off
What is the agar diffusion method?
- A disc is impregnated with antibiotic
- As distance from the disc increases, the concentration of antibiotic decreases logarithmically
- The border of the clear zone is the MIC
- This is time-consuming
What type of antibiotics should be used in nosocomial infections and severe sepsis?
Broad-spectrum
Why should as large a sample as possible be sent when identifying organisms?
More sample means higher sensitivity
Name two methods of rapid antigen detection.
- PCR
- Immunofluorescence
What factors about the site of infection can affect antibiotic choice?
- pH at the infection site
- Lipid-solubility of the drug
- Ability to penetrate the blood-brain barrier
Which two types of infection require special consideration because they are difficult to penetrate with antibiotics?
- Osteomyelitis
- Endocarditis
In which circumstances would you avoid IM administration of antibiotics?
- Bleeding tendency
- Drug is locally irritant
Describe the type I pattern of antibiotic activity. Give an example of an antibiotic of this type.
- Concentration-dependent killing
- Peak above the MIC (Cmax) is the most important parameter
- Example: aminoglycosides
- These drugs tend to be given as one big dose
- The benefits of achieving a higher Cmax must be balanced with the increased toxicity
- Trough concentration should also be measured to ensure that the drug is being eliminated (this determines the frequency of drug administration)
Describe the type II pattern of antibiotic activity. Give an example of an antibiotic of this type.
- Time-dependent killing
- Time spent above the MIC is the most important factor
- Example: penicillins
- Therefore, penicillins need to be given frequently
Describe the type III pattern of antibiotic activity. Give an example of an antibiotic of this type.
- Concentration and time-dependent
- AUC above the MIC is the most important factor
- Example: vancomycin
NOTE: infusions may be used to maintain an AUC above the MIC
What are the main side-effects of aminoglycosides?
Ototoxicity and nephrotoxicity
Name two common organisms that cause skin infections.
- Streptococcus pyogenes*
- Staphylococcus aureus*
How are simple skin infections treated?
Flucloxacillin
NOTE: unless penicillin allergic or MRSA
How should invasive group A streptococcal infection be treated?
- Aggressive and early debridement
- Early use of antibiotics (e.g. clindamycin)
- Use of IVIG
What is the eagle effect?
- There is a relative lack of efficacy of beta-lactams in infections with a high bacterial burden
- This is because beta-lactams only work on dividing bacteria
- In cases of high bacterial burden, a lot of bacteria may be in the stationary phase of the cell cycle
List some common organisms that cause bacterial respiratory tract infections.
- Streptococcus pneumoniae
- Haemophilus influenzae
- Moraxella catarrhalis
- Atypical: Legionella, Mycoplasma, Chlamydia
What is used to treat:
- Pharyngitis
- CAP (mild)
- CAP (severe)
- Pharyngitis = Penicillin V (10 days)
2. CAP (mild) = Amoxicillin
3. CAP (severe) = Co-amoxiclav and clarithromycin
List some treatment options for hospital-acquired pneumonia.
- Cephalosporins
- Ciprofloxacin
- Tazocin
- If MRSA, consider adding vancomycin
List the main pathogens that cause meningitis.
- Neisseria meningitidis
- Streptococcus pneumoniae
- Listeria monocytogenes (in the very young, elderly and immunocompromised)
What is the mainstay of treatment for bacterial meningitis?
Ceftriaxone
NOTE: consider adding amoxicillin if Listeria is likely
How is menigitis in babies < 3 months treated?
Cefotaxime + amoxicillin
NOTE: ceftriaxone is NOT used in neonates because it displaces bilirubin from albumin and causes biliary sludging
What are the treatment options for N. meningitidis meningitis?
- Benzylpenicillin
- Ceftriaxone or cefotaxime
Outline the treatment of:
- Simple cystitis
- Hospital-acquired UTI
- Infected urinary catheter
- Simple cystitis - trimethoprim (3 days)
- Hospital-acquired UTI - cephalexin or co-amoxiclav
- Infected urinary catheter - change catheter under gentamicin cover
How is C. difficile colitis treated?
- Stop the offending antibiotic (usually a cephalosporin)
- If severe, treat with metronidazole or vancomycin
What are some important things to consider if there is no response to antibiotics within 48 hours?
- Does the patient have a bacterial infection?
- Is there a persistent focus of infection?
- Is there a deep-seated collection that requires drainage?
- Could the patient have bacterial endocarditis?
- Is the dose appropriate?
- Is there another infection present (consider Candida)?
