Antibiotics Flashcards
Antibiotic targets
Peptidoglycan cell wall (Beta-lactams, Vancomycin)
Ribosomes (Macrolides, Clindamycin, Chloramphenicol, Gentamicin, Doxycycline)
DNA (Quinolones, Rifampicin)
Metabolism (Trimethoprim, Metronidazole)
Bactericidal
Sterilises infected site by directly killing bacteria
Releases toxins and inflammatory material
Bacteriostatic
Suppresses growth but doesn’t achieve sterility
Requires additional immune cell-mediated killing
Anaerobic bacteria
Bacteroids
Clostridium
Aerobic gram + bacteria
Thick peptidoglycan cell wall, stain purple
Streptococcus
Enterococcus
Staphylococcus
Aerobic Gram - bacteria
Thin peptidoglycan cell wall, stain pink
Outer membrane and periplasm
E. coli Other coliforms Neisseria Haemophilus Pseudomonas Klebsiella pneumoniae
Guided therapy
Antibiotic selected specific to identified bacteria
Narrow spectrum - little impact on colonisation/resistance
Empirical therapy
Used when cannot wait for culture result
Best educated guess based on clinical presentation
Broad spectrum - big impact on colonisation/resistance
Beta-lactams
Inhibits cross linking of peptidoglycan cell wall
Frequent gram -ve and Staph resistance due to beta-lactamase production
Penicillins
Cephalosporins
Carbapenems
Monobactams
Benzylpenicillin
Strep
Neisseria
Clostridium
Main use in Erysipelas
IV
Flucloxacillin
Staph / Strep soft tissue infection
Oral
Amoxicillin
Strep Enterococcus Neisseria Haemophilus Clostridium
Oral
Co-amoxiclav
Amoxicillin with Clavulonic acid (beta-lactamase inhibitor)
Tazocin
Piperacillin with tazobactam (beta-lactamase inhibitor)
Adverse effects of penicillins
GI toxicity
- Nausea, vomiting
- Diarrhoea
- Cholestasis
Hypersensitivity
- Type I or IV
- Interstitial nephritis
- Cross-reactivity low
Infection
- Candidiasis
- C. diff
- Resistant bacteria
Seizure
Haemolysis
Leukopaenia
Ceftriaxone (cephalosporins)
Broad spec - except pseudomonas and enterococcus
More resistant to beta-lactamases than penicillins
Meropenem (carbapenems)
Ultra-broad spec
Resistant to beta-lactamases
Vancomycin (glycopeptides)
TREATS MRSA
Not dependent on PBP so effective against resistant bacteria
IV (oral for C.diff)
Adverse effects
- nephrotoxicity, red-man syndrome, ototoxicity
- narrow therapeutic range
- beware under/overdosing
50s subunit targets
Macrolides
Clindamycin
Chloramphenicol
Erythromycin, Clarithromycin, Azithromycin (macrolides)
Gram +
Resp gram -
Atypicals
Oral
Adverse effects
- diarrhoea, vomiting
- QT prolongation
- hearing loss
- Clarithromycin has >400 drug interactions including simvastatin, atorvastatin and warfarin
Clindamycin
Staph
Strep
Anaeobes
Stops exotoxin production so used in toxic shock syndrome and necrotising fascitis
Oral
Chloramphenicol
Broad spec
Bacterial meningitis when beta-lactam allergy
Very toxic - BM suppression, aplastic anaemia, optic neuritis
30s subunit targets
Aminoglycosides
Tetracyclines
Gentamicin (aminoglycoside)
Broad spec
Once-daliy dose for 3 days only
Initial high dose to achieve bactericidal effect
Bacteriostatic effect lasts long post-antibiotic
Trough level measured to monitor clearance
Very toxic - nephrotoxicity, ototoxicity, neuromuscular blockade in myasthenia gravis
Not used in pregnancy
