Antibiotics Flashcards
What in an infection?
Invasion and multiplication of pathogenic microbes
What is the difference between broad and narrow spectrum antibiotics?
Broad spectrum antibiotics are active against many bacteria but may kill normal flora whereas narrow spectrum are active against few bacteria but may not kill all pathogens
What is the difference between bactericidal and bacteriostatic?
Bactericidal = kills bacteria by affecting bacterial cell wall
Bacteriostatic = inhibits growth of bacteria by affecting RNA and DNA (usually sufficient as bacteria do not live that long)
What is the minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC)?
MBC = lowest concentration that kills 99.95 of a population
MIC = lowest concentration which inhibits visible growth of bacteria
What is the breakpoint?
MIC cut-off which separates strains where there is a high likelihood of treatment succeeding from those where treatment is more likely to fail
What are the characteristic features of a bacteria?
1-10μm in size DNA as a single chromosome (prokaryotes) Independent metabolism and no organelles Cell wall (different from cell membranes of host organism) Can be gram +ve/-ve Can be coccus or bacillus/rod-shaped
What is the different between bacteria that gram stain positive and negative?
Gram +ve = peptidoglycan cell wall
Gram -ve = LPS cell wall
Give an example of each type of bacteria.
Gram +ve cocci = Staphylococcus species
Gram +ve bacilli = Bacillus anthracis
Gram -ve cocci = Neisseria meningitidis
Gram -ve bacilli = E. coli
What are the main potential targets of antibiotics?
- Bacterial cell wall (bactericidal): Beta-lactams, Cephalosporins + Glycopeptides (e.g. Vancomycin)
- Bacterial RNA + protein synthesis (bacteriostatic): Macrolides, Lincosamides, Tetracyclines + Aminoglycosides
- Bacterial DNA structure + function (bactericidal in high dose): Quinolones, Nitroimidazoles + Nitrofurantoin
- Folic acid synthesis (bacteriostatic): Trimethoprim + Sulphonamides
What is the problem with targeting folic acid synthesis?
Bacterial AND human cells utilise it for DNA synthesis so it can produce quite a lot of side effects
What is the action of beta-lactam antibiotics? What are the different types?
Block bacterial cell wall synthesis causing cell lysis (bactericidal)
Examples:
- Amoxicillin (enhanced uptake by bacteria) e.g. LRTI
- Flucloxacillin (penicillinase-resistant): SSTI
- Co-amoxiclav (beta-lactamase inhibitor): mixed infections
Is allergy to beta-lactams common?
No, a lot of people think they are allergic but usually they are just intolerant so make sure to ask what their reaction is to penicillin
What do beta-lactams have poor activity against?
IC organisms e.g. Legionella and those w/o cell wall e.g. Chlamydia, Mycoplasma, Rickettsia and Mycobacteria
What is the action of cephalosporin antibiotics? Give a example.
Block bacterial cell wall synthesis causing cell lysis (bactericidal) with later generations having increased spectrum of activity but also kill more flora and decreased activity against gram +ve’s
Example:
Ceftriaxone (4th gen): abdominal sepsis, bacterial meningitis and orthopaedic infections
If a patient has a beta-lactam allergy, what else are they most likely allergic too?
Cephalosporins as they are closely-related by the beta-lactam ring
Why do cephalosporins have limited use?
Clostridium Difficile Associated Diarrhoea (CDAD) = most notorious complication of broad-spectrum antibiotics that is difficult to get rid of with severe and life-threatening consequences esp. in frail patients
What is the action of carbapenem antibiotics? Give an example.
Block bacterial cell wall synthesis causing cell lysis (bacteriostatic) used for infections in ITUs and complex/multi-drug resistant UTIs
Example: Meropenem
Why are carbapenem antibiotics not commonly used?
They are the most broad spectrum AND least antibiotic resistant so we want to keep them reserved and only use them when absolutely necessary
What is the action of macrolide antibiotics? Give an example.
Inhibit RNA and bacterial protein synthesis (bacteriostatic) used for URTI, LRTI, SSTI (in place of penicillins) or atypical LRTIs (IC organisms)
Example: Erythromycin
What is the action of lincosamide antibiotics? Give an example.
Inhibit RNA and bacterial protein synthesis (bacteriostatic) used for SSTI in place of penicillins when IV access is limited as it has excellent bioavailability and tissue penetration when taken orally
Example: Clindamycin
What is the action of tetracycline antibiotics? Give an example.
Inhibit RNA and bacterial protein synthesis (bacteriostatic) used for atypical bacteria that lack the usual cell wall e.g. Chlamydia, Mycoplasma or Rickettsia infections (e.g. Typhus) but GI tolerance and photosensitivity can limit use as a rash can occur in sunlight
Example: Doxycycline
What is the action of quinolone antibiotics? Give an example.
Target bacterial DNA structure and function by inhibiting DNA coiling (bacteriostatic at high dose) used for gram -ve infection (exc. anaerobes) and MRSA but associated with CDAD
Example: Ciprofloxacin
What is the action of nitroimidazoles? Give an example.
Target bacterial DNA structure and function by inhibiting DNA synthesis (bactericidal at high dose) used for anaerobic infections e.g. abscesses and tooth infections
Example: Metronidazole
What would be a GPs first choice for a simple uncomplicated urinary tract infection (UTI)?
Trimethoprim (anti-folate) or Nitrofurantoin
When choosing an antibiotic, what must you consider?
- Don’t forget sepsis and supportive treatments
- Dont forget to use the diagnostic process and send microbiology tests
- Consider factors affecting antibiotic choice
- Consider antibiotic guidelines
If a patient has severe sepsis from a lower respiratory traction infection (LRTI), what must you do?
Sepsis 6 care bundle:
- High flow oxygen
- Blood cultures
- Give empirical IV antibiotics
- Measure FBC and serum lactate
- Start IV fluid resuscitation
- Start accurate UO measurements
What should you consider when treating patients with lower respiratory tract infections (LRTIs)?
- Oxygen if hypoxic
- Antimicrobials once diagnostic sample sent
- IV fluids if AKI signs
- Bronchodilators/steroids for bronchitis
- Saline nebuliser and chest physiotherapy for expectoration
- Ventilatory support if resp. failure
What is CURB-65?
A scoring system scoring the severity of a lower respiratory tract infection (LRTI):
C = confusion
U = urea > 7mmol/L
R = RR > 30/min
B = BP < 90mmHg systolic or < 60mmHg diastole
65 = > 65 years old
If score > 1 = admit
If score > 2 = IV treatment
What is the diagnostic process step-by-step?
- History: PC, HPC, PMH, ADT, FH, SH and ROS
- Examination: general, CVS, RS, ABDO, NS, LMS etc.
- Differential diagnosis
- Investigations: bedside tests, body fluids, imaging, physiology and histopathology
- Diagnosis
- Treatment
What factors affect antibiotic choice?
- Organism: known OR most likely organism +/- sensitivities and resistance profile
- Patient:
- Allergy/intolerance
- Renal/liver function
- Severity of infection or immunocompromised
- Risk of antibiotic-associated infection
- Route of administration
- Interactions w/ other medication
- Age or ethnic group
- Pregnant, breast-feeding or taking oral contraception
When are antibiotic guidelines most important?
When no organism is identified and you are giving empirical treatment
Where can you access antibiotic guidelines?
- BNF has general guidelines
2. Local guidelines due to local epidemiology, antibiotic resistance, cost etc. which changes with area
What is the aim of antibiotic guidelines?
To produce effective and efficient treatment whilst reducing over-prescribing and use of broad spectrum antibiotics as this can lead to antibiotic resistance and other complications such as adverse effects or antibiotic associated infections
