SCRIPT: antimicrobials Flashcards
Start Smart, Then Focus.
a) How to start smart
b) When to review
c) What to review
a) - Obtain cultures prior to starting treatment where appropriate (but treatment should not be delayed)
- Take a drug allergy history.
- Start IV antibiotics within ONE hour of recognising sepsis
- Comply with local prescribing guidelines.
- Document the indication*, severity of infection, dose, route and frequency on prescription and in the notes.
- State a review or stop date (in notes and drug chart)
- Consult micro / pharmacist for advice if needed
- If this is confidential or sensitive (eg. HIV), document only in notes (on prescription, write ‘see notes for indication’)
b) Review after 48 - 72 hours
c) Review patient and response to infection, etc.
Consider …
- continuing treatment (if some response)
- stopping antibiotics (if no evidence of infection)
- changing/ escalating (if no response/ patient is worse)
- switching route (eg. IV to oral, or vice-versa)
- administering as outpatient (OPAT)
Document any changes in the notes with an updated management plan and set a further review date
Patient with e.coli sepsis - found to be sensitive to nitrofurantoin, ciprofloxacin and pivmecillinam.
a) Which would generally be the best choice and why?
b) What are the risks of this choice?
a) Ciprofloxacin.
- Nitro and pivmecillinam do not achieve good blood concentrations as they are concentrated in the urine (this is why they are good for lower UTIs)
- Cipro achieves good serum levels
b) c. diff
Primary care - TARGET toolkits
https://www.gov.uk/government/publications/managing-common-infections-guidance-for-primary-care
Gram positive vs. negative*.
a) Cell wall and staining difference
b) Example G+ and G- bugs
c) Antibiotic with exclusively G+ action
d) Antibiotics better for G- bugs (or G+ enterococci)
e) Antibiotic only used for anaerobes (G+ or G-)
f) Broad spectrum Abx
*Note: most bugs have cover across G+ and G- (not a simple dichotomy)
a) - G+ bugs have thicker peptidoglycan cell wall layer
- So retain gram staining (purple) and can’t be destained
b) G+ bugs: staph, strep, c.diff, entorococcus,
- G- bugs: e.coli, neisseria, haemophilus, klebsiella, moraxella, proteus, legionella, pseudomonas
c) Glycopeptides: vancomycin, teicoplanin
d) - Cipro
- Aminoglycosides (eg. gentamicin)
e) Metronidazole
- Others useful for anaerobes:
f) - Co-amoxiclav, tazocin
- Meropenem
- Moxifloxacin
- Cephalop
Antibiotic - mechanisms of action.
a) Beta-lactams (penicillins, cephalosporins and carbapenems)
b) Glycopeptides (eg. vancomycin and teicoplanin)
c) Macrolides (eg. clarithromycin) and tetracyclines (eg. doxycycline)
d) Aminoglycosides (eg. gentamicin, tobramycin, amikacin, streptomycin, neomycin)
e) Quinolones (eg. cipro, levo)
f) Metronidazole
g) Trimethoprim
a) Inhibit cell wall synthesis
b) Inhibit different part of cell wall synthesis
c) Bacteriostatic agents - they inhibit protein synthesis, stopping the cell from growing
d) Bactericidal agents; they inhibit a vital cellular process which leads to cell death
- useful when combined with cell wall antibiotic to attack bug from different angles
e) Quinolones interfere with DNA synthesis.
f) Metronidazole damages bacterial DNA
- only active against anaerobic bacteria.
g) Trimethoprim interferes with bacterial folate metabolism, resulting in a lack of purine analogues for DNA synthesis.
How bugs evade antibiotics
- Efflux pumps - pump antibiotic out with no effect (eg. pseudomonas)
- Enzymes against certain antiobiotics (eg. extended spectrum beta-lactamase (ESBL) producers, carbapenem-resistant enterobacteria, aminoglycoside-modiying enzymes)
- Mutations to prevent binding (eg. MRSA)
Factors affecting choice of antibiotic
- National/local antimicrobial prescribing guidelines
- Spectrum of antimicrobial activity (e.g. broad-spectrum vs narrow spectrum)
- Site of infection
- Cultures and sensitivities. If the causative organism is unknown, consider the type of organism most likely to be causing the infection at a particular site (empirical)
- Patient factors (e.g. allergies, age, drug history, co-morbidities, contraindications to treatment)
- Route of administration
- Duration of treatment/intended review date
Why macrolides useful for atypical pneumonias
- Act intracellularly (legionella resides in intracellular space and beta-lactams cannot act here)
- Mycoplasma has no cell wall for beta lactams to act on; whereas macrolides can inhibit their protein synthesis
Communicating with the microbiologist.
- important info to provide them
- Any known previous colonisation and/or infection with an organism with antibacterial susceptibilities.
- Any known allergies - especially to antibacterials.
- Any recent hospitalisation (other hospitals may harbour different organisms to yours).
- Any recent procedures or surgery.
- Any obvious source of current infection
Patient in hospital is on co-amoxiclav for CAP. Develops diarrhoea, abdo pain and pyrexia.
a) Diagnosis
b) Other drug causes of this
c) What should you do?
a) c. diff
b) - 4 Cs - co-amox, cipro, clindamycin, cephalosporins
- Omeprazole
c) - Stool cultures should be sent to microbiology to test for C. difficile toxin and antigen.
- Co-amoxiclav should be stopped.
- If antibacterials still required to treat CAP, a narrower spectrum agent should be chosen.
- Empirical metronidazole should be started while awaiting the stool culture results.
- Given her abdominal pain and pyrexia, she should be reviewed by the surgical team to exclude colitis and toxic megacolon.
- Assess the patient for sepsis, follow your local organisations clinical screening toolkits
IV antibiotics.
a) Why MUST the first dose of antibiotics in sepsis be given IV?
b) Why are IV antibiotics generally better for systemic infection?
c) In most cases, can be switched to oral after how long?
d) For which infections are IV antibiotics often needed for longer courses?
a) In systemic infections, IV antibiotics should be first line. Particularly important for the first dose to ensure quick and effective systemic distribution of ABx
b) 100% bioavailability, so should have a good distribution throughout body tissues and therefore a good effect at receptor sites
c) 24 - 72 hours
d) Deep infections:
- Osteomyelitis
- Endocarditis
Antimicrobial stewardship.
a) When prescribing antibiotics
b) Self management strategies (primary care)
a) - Ensure clinical need (good evidence of bacterial infection/ high-risk patients)
- Narrow-spectrum where possible (especially if culture + sensitivity results available)
- Correct dose, frequency, duration and route
- Consider if delayed (back-up) prescription is possible
b) - Fluids
- Bed rest
- Analgesia
- Safety net - when to seek medical attention
84 year old patient presents with symptoms suggestive of both a chest infection and catheter-associated UTI. He is on methotrexate.
a) What would be an appropriate first choice of ABx?
b) Other considerations
c) Would a urine dipstick be useful in this setting?
d) What antibiotic is contraindicated in patients on methotrexate?
a) Co-amoxiclav.
- broad spectrum antibiotic to G+ and G- bugs, which should cover most chest and urine infections
- adding trimethoprim/ nitro/ pivmecillinam would probably be unnecessary
b) - Co-amoxiclav one of the 4 big risk antibiotics for c.diff infection
- Also need to ensure no penicillin allergy
- Take urine / sputum culture if possible to guide further therapy
c) No. As it is a catheter-associated UTI (after one month all patients with catheter will have bacteriuria and be dipstick-positive)
- Management based on symptoms
- Urine sample taken and catheter changed
d) Trimethoprim (as they are both folate antagonists, which can lead to increased risk of blood dyscrasias)
Patient counselling.
- Importance of compliance
- What to do if dose missed (may differ by drug)
- Safety netting, self management
- How to take (eg. with food - metronidazole; on empty stomach - pen V)
- Interactions (eg. with alcohol - metronidazole; with COCP - rifampicin; with other drugs - erythromycin)
Restricted antimicrobials - rationale
- Broad-spectrum agents, where inappropriate use would promote development of resistance
- Agents reserved for serious infections where MDR bugs are a known risk
- Toxic agents - their use may be limited in duration or they require specialist monitoring
- Expensive drugs - inappropriate use may waste limited resources
