Microbiology 3 - Antimicrobial Agents 2 Flashcards
What mnemonic can be used to help decide which antibiotic to use?
Other factors:
CHAOS
Choice depends on the:
Host charcteristics
Antimicrobial susceptibilities of the
Organism itself, as well as the
Site of infection
Other:
- cost of drug
- pharamcokinetics - absorption, distribution, elimination
- spectrum- use narrow spectrum where possible
- bactericidal>bacteriostatic
- route of administration
What is the Minimum Inhibitory Concentration and Breakpoint of an antibiotic useful for?
Working out sensitivity
MIC > breakpoint = resistant
MIC < breakpoint = sensitive
MIC: minimum inhibitory concentration
Breakpoint: pre-determined concentration required to inhibit the growth of an organism
so if MIC < breakpoint –> organism is susceptible
What antibiotic should be given for gram pos cocci in clusters?
Flucloxacillin
What antibiotic should be given empirically for gram neg cocci?
Ceftriaxone (could be meningococcus)
What is the “eagle effect”?
Increasing the penicillin dose –> decreasing antibacterial activitity after a point
This is because:
- penicillins are only effective when cells are dividing as they inhibit cell wall synthesis
- when you have high bacterial load, bacteria might be in stationary phase of growth - so not susceptible to penicillins
How does the choice of antibiotic to treat UTI differ between community and hospital?
Community: nitrofurantoin/ trimethoprim
Hospital: cephalexin/ augmentin
What are the reasons for misusing antibiotics?
- no infection present
- inappropriate duration
- wrong drug
- wrong dosage
Common side effects of antibiotics
GI upset (i.e. diarrhoea)- MOST COMMON
Fever and rash (SJS)
Renal dysfunction
Acute anaphylaxis
Liver dysfunction (abnormal LFTs seen), Hepatitis
Which antibiotcis should not be given to children?
Which antibiotics should not be given to pregnant women?
Tetracyclines - because they stain teeth yellow
Trimethoprim- as it is a folate antagonist–>NTD
*tetracycline is also contraindicated in pregnancy
How does the infection site influence the choice of antibiotics used?
Factors to consider:
- pH
- lipid solubility
- ability to penetrate blood brain barrier
Which areas of the body are hard to treat with antibiotics?
- bone- osteomyelitis
- brain - meningitis
- heart- endocarditis
Indications for IV antibiotics?
- Sepsis
- Site inaccessible - brian, heart, bone
- some antibiotcis not absorbed well orally - eg aminoglycosides
When do you switch from IV to PO antibiotics?
Usually when patient is stable on IV antibioitics for 48 hours
(except for deep sited infections such as meningitis)
Specific infection for which you use IM administration?
Is IM adinsitration advisable long term?
Gonorrhoea- IM ceftriaxone
Not for long term use
What is Type 1 pattern of activity and which antibiotics use this effect?
Type 1: concentration dependent
*try to maximise cMax
Drugs: aminoglycosides eg gentamicin
Administration: generally as single dose PO to maximise concentration
Risks: ototoxicity and nephrotoxicity
What is Type II patern of activity and which drugs use it?
Type II: time dependent - maximise time above MIC.
MOA: given frequently (3-4 times per day). Looking into giving IV as well
Drugs:
- penicillins
- linezolid
- erythromycin
- cephalosporin
- carbapenem
What is Type III activity? Which drugs?
Both concentration dependent and time dependent : i.e. depends on AUC under MIC
**given as INFUSIONS to maximise AUC
Drugs:
- vancomycin
- tetracycline
- macrolides
- oxalozidinediones
Which bacteria commonly cause skin infections?
Examples of skin infections
Treatment of skin infections
Staph
Group B strep
Examples: impetigo, cellulitis, wound infections
Treatment: flucloxacillin
*unless penicillin allergy or MRSA –> VANCOMYCIN
INvasive skin infections caused by Group A streptococcus
Treatment?
GAS- strep pyogenes
Causes cellulitis and necrotizing fasciitis
Treatment:
Adjunctive use of protein synthesis inhibitors - eg clindamycin
Most common organisms causing CAP
- Typical
Strep pneumoniae
Haemophilius influenzae
Moxarella Catharlis (only in COPD patients)
- Atypical - usually more severe
Mycoplasma
Chlamydia
Legionella
Empicial antibiotic regime for CAP
Mild: Amoxicillin + clarithromycin
Severe: co-amoxiclav + clarithryomycin
(Clavulinic acid- cover against organisms resistant to amoxicillin)
Organisms causing HAP
Most common: enterobacteracia (gram negatives) - e coli, klebsiella
Second most common: Staph Aureus
Pseudomonas
Fungi
Actinobacter Baumanii
Empirical antibiotic regime for HAP
1) First line
2) Second line- used in ITU??
1) First line:
Ciprofloxacilin + vancomycin
Cipro: cover against gram negatives i.e. enterobacteraciae (most common cause of HAP)
Vancomycin: cover against gram positives i.e. MRSA
2) Second line (used in ITU)
Piptazobactam + vancomycin
Piptazobactam: provides cover against pseudomonas - 3rd most common cause of HAP
Vancomycin: cover against gram positive MRSA
Specific antibiotic therapy for MRSA
Vancomycin
Specific antibiotic therapy for pseudomonas
Piptazobactam/ciprofloxacin +/- gentamicin
Piptazobactam: combination of piperacillin (broad spectrum pencillin) + tazobactam (beta lactamase inhibitor)
Common organisms causing bacterial meningitis
Treatment:
N. meningitidis
H. influenzae
Listeria monocytogenes
Treatment: ceftriaxone +/- amoxicillin
Indications for adding amoxicillin: >65 or pregnant women
Treatment of bacterial meningitis in babies
Cefotaxime + amoxicilli
*not ceftriaxone because of risk of jaundice
Empirical therapy for cystitis
Uncomplicated cystitis
first line nitrofurantoin
*not trimethoprim because of increasing resistance
In whcih patients is nitrofurantoin not recommedned?
Pregnant women, especially in third trimester
When should you take nitrofurantoin?
After emptying bladder because it concentrates in the bladder
How do you treat catheter associated UTIs?
- *• Remove catheter** (but give stat doses before removal of infected catheter)
- *• Gentamicin or Amikacin** (stat 30-60 mins before the procedure)
Treatment of pyelonephritis
Broad spectrum antibiotics
Co-amoxiclav + gentamicin
(or can use amikacin instead of gentamicin)
Treatment of C difficile colitis
STOP the offending antibiotic (usually a cephalosporin)
If SEVERE, treat with:
PO metronidazole
If the above fails, use PO vancomycin
