Antimicrobial Agents Flashcards
What are some mis-uses of anitmicrobials (5)
No infection present Selection of incorrect drug Inadequate or excessive dose Inappropriate duration of therapy Expensive agent used when cheaper is available
What are some adverse effects associated with antimicrobials (5)
GI upset Fever and rash Renal dysfunction Acute anaphylaxis Hepatitis
What does CHAOS refer to when talking about antibiotics (5)
CHOICE of the correct antimicrobial depends upon then... HOST characteristics ANTIMICROBIAL susceptibilities of the... ORGANISM itself and also the... SITE of the infection
What influences the choice of antibiotic (9)
Use narrow spectrum if possible
Use bactericidal drugs if possible
Ideally choice should be based upon a bacteriological diagnosis (otherwise best guess, based upon likely differential diagnosis)
Consider local sensitivity patterns
Patient characteristics
Cost
Pharmakokinetics (absorption, distribution, elimination)
Route of administration (IV for serious infection or if patient not absorbing PO, or need to access deep sites of CNS)
Dosage (age, renal.hepatic function, drug monitoring, allergy)
What host factors influence drug choice (5)
Allergy Renal function Hepatic function Age Genetics
What is the agar disc diffusion method used for
Determine bacterial susceptibilities.
Antibiotic-impregnated disc absorbs moisture from the agar; antibiotic diffuses into the agar medium.
As distance from the disc increases, there is a logarathmic reduction in the [antibiotic].
[diffused antibiotic] at the interface of growing and inhibited bacteria ~ MIC
When should specimens for culture be collected
Prior to starting antibiotics
What antibiotic choice is appropriate for nosocomial pneumonia and severe sepsis
Immediate initiation of broad spectrum antibiotics
The best antibiotic should be prescribed first, based on the patient’s risk factors, suspected pathogen and local resistance patterns.
How can the causative organisms be identified preliminarily (2)
Gram stain
Rapid antigen detection
What samples are suitable for gram stain (3)
CSF
Joint aspirate
Pus
What are some rapid antigen detection methods (2)
Immunoflouresence
PCR
What infection site factors will affect the efficacy of the antimicrobial (3)
pH of infection site
Lipid-solubility of the drug
Ability to penetrate the BBB
What infections need special considerations when treating (2)
Endocarditis
Osteomyelitis
When should IV antibiotics be used
Serious (or deep-seated) infection
When should PO antibiotics be avoided
Poor GI function or vomiting
When are IM antibiotics not suitable (2)
Not an option for long-term use
Avoid if bleeding tendency or drug is locally irritant
What is a problem associated with topical antibiotic use
Limited application and may cause local sensitisation
When is IV to PO recommended in hospital antibiotic treatment
If the patient has stabilised after 48 hours of IV therapy
What is the goal of therapy for antibiotics that are concentration-dependent at killing the organisms
Maximise concentration of antibiotic
What are some antibiotics that are concentration dependent (4)
Aminoglycosides
Daptomycin
Fluoroquinolines
Ketolides
What is the goal of therapy in drugs that are time-dependent
Maximize duration of therapy
What are some antibiotics that are time dependent (5)
Carbapenems Cephalosporins Erythromycin Linezolid Penicillins
What are some drugs that are time-dependent with moderate to prolonged persistent effects
Maximize amount of drug
What are some drugs that are time-dependent with moderate to prolonged persistent effects (5)
Azithromycin Clindamycin Oxazolidinones Tetracyclines Vancomycin
How long should antibiotics be given for n.meningitidis meningitis
7 days
How long should antibiotics be given for acute osteomyelitis (adult)
6 weeks
How long should antibiotics be given for bacterial endocarditis
4-6 weeks
How long should antibiotics be given for Group A streptococcal pharyngitis
10 days
How long should antibiotics be given for a simple cystitis (in women)
3 days
What organisms are most common in skin infections (2)
Staph. aureus
Beta-haemolytic streptococci
What are the most common skin infections (3)
Impetigo
Cellulitis
Wound infections
What antibiotic should be used to treat skin infections
Flucloxacillin (unless penicillin allergy or MRSA)
What is iGAS
invasive group a streptococcal infection (Toxic shock syndrome)
What is the treatment for iGAS (3)
Aggressive and early debridement
Antibiotics - adjunctive use of protein synthesis inhibitors especially, clinidamycin (also has good skin and soft tissue penetration)
Use of IVIg
What is the eagle effect
Named after Harry Eagle who first described it, originally referred to the paradoxically reduced antibacterial effect of penicillin at high doses, though recent usage generally refers to the relative lack of efficacy of beta-lactam antibacterial drugs on infections having large numbers of bacteria
What is the mechanism of the eagle effect
Penicillin is a bactericidal antibiotic that works by inhibiting cell wall synthesis but this synthesis only occurs when bacteria are actively replicating (or in the log phase of growth).
In cases of extremely high bacterial burden (such as with Group A Strep), bacteria may be in the stationary phase of growth.
In this instance since no bacteria are actively replicating (presumably due to nutrient restriction) penicillin has no activity.
What are some RTIs (3)
Pharyngitis
Community acquired pneumonia (mild)
Community acquired pneumonia (severe)
What is the treatment for pharyngitis
Benzyl penicillin x 10 days
What is the treatment for mild community acquired pneumonia
Amoxicillin
What is the treatment for severe community-acquired pneumonia (2)
Co-amoxiclav and clarithromycin
What increases the risk of hospital acquired RTIs (2)
Tracheal intubation
Mechanical ventilation
What is the treatment for hospital acquired RTIs (2)
Cephalosporin, ciprofloxacin, piperacillin/tazobactam
If MRSA colonised/risk, consider addition of vancomycin.
What are the main causes of bacterial meningitis (3)
N. meningitidis
S. pneumoniae
+/- listeria in the very young/elderly/immuno-compromised
What is the treatment for bacterial meningitis
Ceftriaxone +/- amoxycillin if listeria is likely.
What is the treatment of meningitis in a baby less than 3 months (2)
Ceftriaxone plus amoxicillin (to cover for listeriosis)
Why is ceftriaxone not used in neonates with bacterial meningitis
It displaces bilirubin from albumin and because it can cause biliary sludging
What is the treatment for neisseria meningitidis
Benzylpenicillin (high dose) or ceftriaxone/cefotaxime
What is the mechanism of penicillin resistance in neisseria meningitidis
The mechanism of relative resistance to penicillin involves, at least in part, the production of altered forms of one of the penicillin-binding proteins.
Although treatment with penicillin is still effective against these relatively resistant strains, there is evidence that low-dose treatment regimens can fail.
Beta-Lactamase production in meningococci is extremely rare but has been reported
What is the treatment for simple cystitis (community)
Trimethoprim x 3 days
What is the treatment for hospital-acquired UTI (commonest type of HAI) (2)
Cephalexin or augmentin
What must be done in a hospital acquired UTI if there is also a catheter present
Change catheter under gentamicin cover
How is c.difficile colitis managed (3)
STOP offending antibiotic (usually a cephalosporin)
If severe, treat with PO metronidazole
If above fails, use PO vancomycin
If antibiotics have not worked in 48 hours, what questions must be asked (6)
Does the patient really have a bacterial infection? (Have I collected the relevant cultures?)
Is there a persistent focus present (e.g. an infected vascular or urinary catheter)?
Is there a deep-seated collection (e.g. intra-abdominal) that requires drainage?
Could the patient have bacterial endocarditis?
Am I using the correct dose of the antimicrobial?
Is another infection present (esp consider Candida)?
