Flashcards in Seminars - Exam 2 and 3 Deck (32):
What two purposes can antibiotics be used for?
- immunocompromised host
- exposure to certain bacteria
- dental prcedures
What factors could guide the choice of antibiotic?
• Pharmacological determinants of effectiveness
• Drug interactions
• Excretion (renal, hepatic)
• Route of administration
• Dose frequency
• Breastfeeding/pregnancy (risk categories)
• 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?
- 85% of prescriptions
- Organism/susceptibilities not known (“best guess”)
- Broad spectrum
- Often multiple drugs
- More adverse reactions
- More expensive
- 15% of prescriptions
- Organism/susceptibilities known
- Narrow spectrum
- Usually one drug
- Less adverse reactions
- Less expensive
What would be appropriate empiric antibiotic prescribing?
1. Establish the clinical syndrome
2. Known likely pathogens
3. Understand their probable % susceptibilities
4. 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
– Clonal expansion (vertical transmission)
– Mobile genetic elements (horizontal transmission)
What are two strategies to reduce antibiotic resistance?
1. “Antimicrobial stewardship”
– Reducing the selective pressure by
improving antibiotic prescribing
– 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
– Ward based patient/chart review by IDPhysician/pharmacist
2. Prevent the secondary spread of resistance
– Hygiene and cleaning
- patient isolation
- personal protective equipment
What are some of the downsides to screening?
- false alarms
- over diagnosis
- false reassurance
- 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:
Why does early detection from screening not necessarily mean good prognosis?
a) Lead time bias – there is a delay between the time when the disease is detected and when it is likely to produce symptoms and be diagnosed without screening. Because patient is diagnosed earlier, it may seem like they are living longer – apparent increase in life expectancy (lead time). ‘Disease time’ is increased
b) Length-time bias - Slowly progressing variants of disease remain in a pre-symptomatic (but screen-detectable) stage for longer than rapidly progressing variants of the same disease. Hence, screening is more likely to detect slowly progressing cases. Screen detected cases appear to live longer because they have a slower progression.
The equity of screening – what are some of the factors to consider?
- opportunity cost
- might benefit rich, not poor
- privileged segments of society who take part will insist on appropriate treatment for any potential problems – divert resources towards them
- unequal distribution
What is the number-needed-to-screen?
The number of people that need to be screened for a given duration to prevent one death or adverse event.
What are the 2 measures that tell us how valid (accurate) as diagnostic test is?
a) Sensitivity – probability of those with the disease correctly detected by the rest
- the true positive ‘rate’
- high sensitivity = few people are missed
- ΣTP/Σcondition present = a/a+c
- if high, negative result will ‘rule out’ disease
b) Specificity – probability of those without the disease correctly excluded by the test
- the true negative ‘rate’
- high specificity = rarely test positive when person doesn’t have disease
- ΣTN/Σcondition absent = d/b+d
- if high, positive will rule in disease
What are the 2 measurements that are used to evaluate the result for an individual?
a) Positive Predictive Value
- given a positive test, probability that the patient ahs the disease
- ΣTP/ΣAll Positives = a/a+b
b) Negative Predictive Value
- given a negative test, the probability that the patient doesn’t have the disease
- ΣTN/ΣAll Negatives = d/c+d
What is the triple test approach to diagnosis?
Three diagnostic components:
- medical history and clinical breast exam
- imaging – mammography and/or ultrasound
- non-excision biopsy – fine needle aspiration cytology and/or core biopsy
It is positive if any component is indeterminate, suspicious or malignant.
The sensitivity of the triple test is greater than any of the individual components alone.
What are the issues to consider with placebos?
- breach of trust, BUT...
- if people find out, might bring profession into disrepute
- waste of money
- not surgery
- even if people are aware it is a placebo it can still be beneficial
- probably ethical in clinical trial
- may be more ethical with terminal patients where there is nothing else left to do
- it's play with non-maleficence (not surgery)
NOTE: the doctor in question can impact the placebo effect - how well dressed they are, tone of voice, professional appearance etc.
What are the issues with therapeutic adherence?
- poor compliance = worse health outcomes
- therefore cost of compliance failure on health system and person
- negative attitude towards therapy because they can't see the positive effects
- some people take other people's drugs - overdose
Why are some people noncompliant?
- not understanding importance
- social support
- comorbitidy (i.e. depression)
- feeling helpless - I'm dying anyway
- personal believes
- insufficient access
- weight gain
What are the factors of EBM?
1. Individual clinical expertise
2. Best external evidence
2. Patient values and expectations
What are complimentary medication?
Any non-prescription medicine, including nutritional supplements & “herbal” preparations
Purchased from: supermarket
health store naturopath homeopath herbalist
mail order/internet grown at home
What are the two categories of medicines in relation to testing?
AUSTR = registered
Tested for safe quality
safety and efficacy. Prescription meds and majority of behind the counter pharmaceuticals are AUSTR
AUSTL = listed
Valued for quality and safety but NOT for efficacy.
What are the issues with CMs?
- therapeutic effects
- drug-drug interactions
- drug-disease interactions
- Adulteration (deliberate) and contamination (inadvertent)
Should multi-vitamins be used in healthy people?
They have either been proven ineffective or no objective evidence for efficacy.
What does informed consent involve in regard to prescriptions?
Person needs to understand:
- health implications of their diagnosis
- nature/purpose of proposed Px
- risks/benefits of Px (and of not consenting)
- alternative approached
- that they can withdraw consent
What are the ethical problems with self prescribing?
- threats to health
- judgement clouded by illness
- loss of objectivity
- no monitoring
- inability to perform examination
NOTE: drugs classified into schedules. S8 self-prescription is not permuted except in a few emergency situation.