Infectious Diseases - Antibiotics Profiles

General Principles

Empirical Therapy

Likely organisms

Severity of infection

Investigations
Microbiological:
Swabs
Fluids e.g. sputum, urine, aspirates
Blood culture
Serology

Bloods

FBC

Inflammatory markers

Radiology

Review Progress

Clinical

Cultures & Sensitivity

Adverse Effects

Penicillins
Inhibit bacterial cell wall synthesis
Well tolerated:

Rash (common)

Anaphylaxis (rare)
Excreted in urine
‘Safe’ in pregnancy
Destroyed by beta-lactamase (S. aureus and some anaerobes)

Except:

Flucloxacillin - beta-lactamase resistant

Amoxycillin & clavulinic acid - beta-lactamase inhibitor, may cause jaundice

Benzylpenicillin (IV) or Penicillin V (oral)
Gram +ve (strep)
Meningococcos
Gram +ve Clostridia species of Anaerobes

Ampicillin/Amoxycillin
Gram +ve (strep)
Gram -ve

Flucloxacillin

1st choice - S. aureus

Co-amoxyclav (amox & clavulinic acid)
Gram +ve (strep)
S. aureus
Gram -ve
Anaerobes

Cephalosporins

Inhibit bacterial cell wall synthesis
Broad spectrum
Well tolerated, though 10% cross-over with penicillin allergy
Excreted in urine
‘Safe’ in pregnancy
Resistant to beta-lactamase (S. aureus and some anaerobes)
x cover Enterococci

Cefuroxime (‘2nd generation’)
Gram +ve
S. aureus (not 1st choice)
Gram -ve

Ceftriaxone (‘3rd generation’)
Gram +ve
S. aureus (not 1st choice)
Meningococcus
Gram -ve

Ceftazidime (‘anti-pseudomonal’)
Gram +ve
S. aureus
Gram -ve
Some Pseudomonas

Aminoglycosides

e.g. Gentamicin

Inhibit bacterial protein synthesis
Reserved for severe Gram –ve infections
IV only
Excreted in urine
Important adverse effects:

Nephrotoxic

Ototoxic
Monitor blood levels
Only use in pregnancy if benefit outweighs risk

Aminoglycosides
Gram -ve

Pseudomonas
Mycobacteria - some, not 1st line

Macrolides

e.g. erythromycin, clarithromycin

Inhibit bacterial protein synthesis
Atypical pneumonias
Patients allergic to penicillins
Well tolerated

GI upset (common)

Jaundice (rare)
Erythromycin inhibits cytochrome P450

Macrolides
Gram +ve

S. aureus

Atypicals

Tetracyclines

Inhibit bacterial protein synthesis
Broad spectrum including most atypicals
Over-used in the ‘60s and ‘70s - widespread resistance
Deposits in bone and teeth - grey staining
Avoid in pregnancy and children < 12 years
May exacerbate renal impairment

Tetracyclines

Gram +ve (Used as empirical alternatives to penicillin in mild/moderate URTI, also used for acne)
Gram -ve
Atypicals (Treatment of choice for microbiologically proven Chlamydia, Rickettsia, Brucella, Borrelia)

Trimethoprim

Bacterial dihydrofolate reductase inhibitor
Broad spectrum, some resistance
Well tolerated
Excreted in urine
Avoid in pregnancy
Useful for empirical treatment of UTI and respiratory infections

Trimethoprim

Gram +ve
Gram -ve

Quinolones

e.g. ciprofloxacin

Inhibits DNA gyrase

Mainly Gram –ve aerobes inc some pseudomonas
Over-used in the ‘80s - widespread resistance
Rarely = seizures or tendon inflammation/rupture
Excreted in urine
Avoid in pregnancy

Quinolones

Meningococcus - Prophylaxis only
Gram -ve
Some Pseudomonas

Glycopeptides

e.g. vancomycin, teicoplanin

Inhibit cell wall synthesis

Severe Gram +ve infections resistant to penicillins
Inc. MRSA (resistant to flucloxacillin)
Vancomycin:

Nephrotoxicity

Ototoxicity

‘Red man’ syndrome
Requires blood levels

Glycopeptides

Gram +ve
S. aureus
Anaerobes - Clostridia species

Metronidazole

Inhibits bacterial DNA synthesis
Anaerobic bacteria and protozoal infections only
Very low resistance
Well tolerated but can cause metallic taste
Avoid if possible in pregnancy

Metronidazole

Anaerobes