Seminars - Exam 2 and 3 Flashcards
What two purposes can antibiotics be used for?
a) prophylaxis
- peri-operative
- immunocompromised host
- exposure to certain bacteria
- dental prcedures
b) treatment
What factors could guide the choice of antibiotic?
- Pharmacological determinants of effectiveness
- Drug interactions
- Excretion (renal, hepatic)
- Route of administration
- Dose frequency
- Cost
- Breastfeeding/pregnancy (risk categories)
- Allergy/hypersensitivity
- Penetration to site of infection
- Need for therapeutic drug monitoring
- Adverse effect profile
What are the important areas of antibiotic resistance?
• MRSA - Methicillin Resistant Staphylococcus aureus (Resistant to all beta-lactam antibiotics)
• VRE - Vancomycin Resistant Enterococci
(Enterococci are inherently resistant to most antibiotics and treatment of serious infection has been limited to amoxycillin or vancomycin)
• ESBLs - Extended Spectrum Beta-lactamases
(Beta-lactamases produced by some Enterobacteriaceae which destroy 3rd generation cephalosporins and other beta lactam antibiotics)
• CREs - Carbapenem Resistant Enterobacteriaceae
(Carbapenems - imipenem & meropenem are very broad spectrum antibiotics, often used in serious infections as a last resort)
What is the difference between empiric and directed antibiotic treatment?
- Empiric
- 85% of prescriptions
- Organism/susceptibilities not known (“best guess”)
- Broad spectrum
- Often multiple drugs
- More adverse reactions
- More expensive - Directed
- 15% of prescriptions
- Organism/susceptibilities known
- Narrow spectrum
- Usually one drug
- Less adverse reactions
- Less expensive
What would be appropriate empiric antibiotic prescribing?
- Establish the clinical syndrome
- Known likely pathogens
- Understand their probable % susceptibilities
- Select an antibiotic with adequate coverage
What guidelines assist antibiotic choice?
Australian Therapeutic Guidelines
What is the MIC of an antibiotic?
Minimum inhibitory concentration (MIC) is the lowest concentration of an antibiotic that will inhibit the growth of an organism
What is the difference between concentration and time dependent drugs in terms of dosage?
- Concentration dependant drugs are given less frequently in bigger doses
- Time dependant drugs are given more frequently in lower doses
What factors determine appropriate route of administration?
- severity of infection (IV?)
- bowel function, i.e. vomitting
- bioavailability. High proportion of Ciprofloxacin is absorbed to rarely give in IV
Why would you need therapeutic drug monitoring for antibiotics?
• Required for antibiotics with a narrow therapeutic index
=ratio of toxic to therapeutic dose/level – Eg vancomycin, gentamycin
How does antibiotic resistance develop?
• De novo chromosomal mutation
– eg ciprofloxacin resistance point mutation occurs in 1:108 bacteria
• Acquired
– Clonal expansion (vertical transmission)
– Mobile genetic elements (horizontal transmission)
What are two strategies to reduce antibiotic resistance?
- “Antimicrobial stewardship”
– Reducing the selective pressure by
improving antibiotic prescribing
FRONT END:
– Restricted formulary - Limited range of antibiotics available in pharmacy
– Restricted approval of antibiotic initiation
– Selective antibiotic susceptibility reporting
– Guidelines and protocols
– Education, audit and feedback
BACK END:
– Ward based patient/chart review by IDPhysician/pharmacist
– Biomarkers
2. Prevent the secondary spread of resistance – Hygiene and cleaning - patient isolation - personal protective equipment - cleaning - decolonisation
What are some of the downsides to screening?
- false alarms
- over diagnosis
- false reassurance
- inconvenient
- unpleasant
- expensive – opportunity cost
- risks they cause – i.e. ionizing radiation
- informed consent
What can screening identify?
- pre-disease abnormality
- early disease
- disease risk markers
What is the aim of screening?
Reduce the burden of the disease in the community, including:
a) incidence
b) morbidity
c) mortality