Antibiotics Flashcards
What percentage of hospital in patients are on antibiotics?
25%
What proportion of the NHS drug budget is spent on antibiotics?
30%
What proportion of antibiotic use is inappropriate?
50%
Give some examples of the relationship between inappropriate drug use and resistance
MRSA
Clostridium difficile
VRE
Resistant enterobacteriaceae
Give some examples of resistant enterobacteriaceae
E.coli
K. pneumoniae
Extended spectrum beta lactamase (ESBL) producers
Carbapenemase producing enterobacteriaceae
Klebsiella producing carbapenemases (KPC)
What can reduce the risk of antibiotic resistance?
Giving less antibiotics
What is the most common antibiotic resistant bacteria at the moment?
E.coli
Which antibiotics is E.coli currently resistant to?
Gentamicin
Ciprofloxacin
Piperacillin - tazobactam
Co-amoxiclav
In what ways are some antibiotics not appropriate?
Indication
Duration
What type of bacteria is E.coli?
Gram negative
What factors affect antibiotic choice?
Patient factors - severity and predisposition (eg. splenectomy)
Antimicrobial resistance - exposure and epidemiology
Microbial aetiology - exposure and focus
Antibiotic knowledge
In clinical practice what do you use to inform your knowledge of antibiotics?
Microguide
What is antimicrobial stewardship?
A set of strategies used to reduce antibiotic resistance, avoid unnecessary cost and improve patient outcomes
Give the 2 antimicrobial stewardship strategies
Primary care - Target
Secondary care - Start smart then focus
What percentage of review and revise decisions are to continue antibiotics?
95%
How can we review and revise antibiotics better?
Recognize that in hospitals antibiotics are usually started empirically
Think about what evidence you would want to have at review
When you review
- Remember antibiotics are harmful
- Did they ever have an infection?
- Are they better now?
- Do the risks of continuing outweigh the benefits?
At what point should you review antibiotics?
48 to 72 hours after starting
What are the two moments when making ood antimicrobial choices?
Initial prescription - microbial aetiology, patient factors, antimicrobial resistance issues, monitoring, guidelines, knowledge
Monitoring and test results - review and revise
What type of antibiotic is amoxicillin?
Penicillin
How does amoxicillin differ from other penicillins?
Longer half life than penicillin 5
Better activity against gram negative bacteria
Good oral bioavailability
Where is amoxicillin used?
Treatment of S.pyogenes infections, pneumococcal infection and coliform infections
Describe the mechanism of action of amoxicillin
Inhibition of bacterial wall synthesis
What is the standard dose of amoxicillin?
250-1000mg 8 hourly
Give the adverse effects of amoxicillin
Allergy
Damage to commensals
Give an interaction of amoxicillin
Can increase the levels of other protein bound drugs
Give the half life of amoxicillin
1 hour
How is amoxicillin excreted?
Urine
List the beta lactam antibiotics
Penicillin G and V Amoxicillin and co amoxiclav Flucloxacillin Piperacillin Cephalexin Cefuroxine Meropenem
Which antibiotic is used for staph aureus infections?
Flucloxacillin
Which antibiotic is regarded the easy oral penicillin?
Amoxicillin
What is co amoxiclav?
Amoxicillin protected against beta lactamases
What is the penicillin used to treat pseudomonas?
Piperacillin
What is another word for a penicillin allergy?
Beta lactam allergy (class effect)
Name the two classes of penicillin allergy
Immediate/Accelerated (Type 1)
Delayed (Type 2)
What percentage of courses result in a type 1 immediate/accelerated penicilin allery?
0.02%
Describe a type 1 immediate/accelerated penicillin allergy
0-72hrs after exposure
IgE and mast cell mediated
Urticaria, wheeze and life threatening
Describe a type 2 delayed penicillin allergy
> 72 hours after exposure
Will worsen with repeated exposure
Does not become the immediate type
What percentage of antibiotic courses result in an delayed penicillin allergy?
2-3%
Describe cephalosporin allergy
Very complicated – lots of potential haptens involved
Not a class effect
Penicillin X-reactivity more with 1st & 2nd generations
Risk ~8% if previous penicillin allergy
Less with 3rd Generation
Describe a history of beta lactam allergy and the outcome of the history
When was it?
What happened – time course and severity?
What was the drug?
Might they have had glandular fever?
Have they had a (different) beta-lactam since?
Good history of anaphylaxis – avoid all beta-lactams
Weak history or of delayed reaction – consider re-challenge.
What drug class is clarythromycin?
Macrolide
What is clarythromycin used to treat?
S.pyogenes infections
Pneumococcal infections
Coliform infections
Cell wall deficient bacteria (chlamydia) so used to also treat genitourinary infection
Give the mechanism of action of clarythromycin
Inhibition of protein synthesis in the bacterial ribosome (50S subunit)
What is the standard dose of clarythromycin?
500mg 12hrly
Describe the drug interactions of clarythromycin
Inhibits enzymes (cytochrome p450) involved in metabolism of other drugs
Give the half life of clarythromycin
1-6hrs
How is clarythromycin excreted?
Bile
How is clarythromycin metabolised?
Hepatic
What are the adverse effects of clarythromycin?
Nausea and diarrhoea
May alter cardiac conduction - arrhythmia
What class of antibiotic is vancomycin?
Glycopeptide
What is vancomycin active against?
Gram positive bacteria
Methicillin resistant staph aureus (MRSA)
Describe the oral bioavailability of vancomycin
Low as it is a big molecule
What is the half life of vancomycin?
4-8 hours
How is vancomycin excreted?
Urine
Give the mechanism of action of vancomycin
Inhibits bacterial cell wall (peptidoglycan) formation by a different target to beta lactams
What is the dose of vancomycin
Dosed according to drug level in blood - narrow therapeutic index. 500-1500mg 12 hourly
What does narrow therapeutic index mean?
Levels needed to kill the patient are close to the levels that are toxic to the patient
What are the adverse effects of vancomycin?
Nephrotoxic and ototoxic
What interactions are there with vancomycin?
Other nephrotoxic and ototoxic drugs
What class of antibiotic is doxycycline?
Antibiotic
What is doxycycline used to treat
Skin, genitourinary and respiratory infections
Gram positive - staph and strep
Gram negative - haemophilus
Cell wall deficient - chlamydia
What interactions does doxycycline have?
Competes for protein binding with digoxin and warfarin
Describe the mechanism of action of doxycycline
Inhibits protein synthesis in bacterial ribosomes (30S subunit)
What is the standard dose of doxycycline?
100-200mg daily
What are the adverse effects of doxycylcine?
Dyspepsia
Photosensitivity
In which patients must doxycycline be avoided?
Pregnant
Children(teeth)
What drug class does nitrofurantoin belong to?
Nitrofuran
What does nitrofuratoin treat?
Wide spectrum E.coli and enterobacteriaceae Staphs Streps Enterococci
Only indicated for UTI treatment
What is the half life of nitrofurantoin?
1 hour
What is the dose of nitrofurantoin?
50mg qds
How does nitrofurantoin work?
Damages bacterial DNA
High resistance threshold
Complex mechanism of action
Describe the use of nitrofurantoin in pregnancy
Safe in early pregnancy
Avoid in late
Is nitrofurantoin safe in renal impairment?
No - doesnt penetrate urine if GFR is low
Which antibiotics seem to have a low C.diff risk?
Nitrofurantoin and doxycycline