Antibiotics

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Penicillin

  • Antibiotics are commonly prescribed medications in the acute setting
  • It is useful to commit to memory the regimes for common infections e.g. pneumonia, urinary tract infections and cellulitis
  • For more unusual infections, returned travellers and recent immigrants consult a microbiologist
  • The relationship between site of infection, likely organism(s) and effective empirical antibiotic has some loose patterns but some regimes have to be memorised by rote
  • A delay in administering antibiotics increases the mortality from sepsis
  • Ongoing treatment may need to be modified after subsequent culture results and sensitivities are returned

ANTIBIOTIC REGIMES BY SITE OF INFECTION

  • The following table is a simplified account for community acquired bacterial infections – outpatient and inpatient based on Australian Therapeutic Guidelines
  • Hospital-in-the home regimes may have alternative or modified regimes to standard inpatient treatments.
  • Post-op prophylaxis and post-surgical infections are not included.

The choice is based on first line empiric prescribing on known sensitivities in Metropolitan areas before culture results are available. (Do not follow this in indigenous populations or Far North Australia)
Unless specified the antibiotic chosen is appropriate also for pregnancy and children.
Use caution in amino-glycoside dosing in patients with renal failure
There may be cheaper or simpler options if the above considerations are not required.
An alternative is suggested for true beta lactam allergy (severe reactions are actually rare and cross-reactivity between penicillins and cephalosporins even less so particularly for the third generation variants).

Clinical condition Outpatient (oral) In-patient (IV) Pencillin ADR
Meningitis Ceftriaxone Vancomycin
Periorbital cellulitis Flucloxacillin
Ceftriaxone
Cephazolin
Ceftriaxone
Bacterial URTI (tonsillitis) Penicillin Penicillin Roxithromycin
LRTI  Roxithromycin Ampicillin +
Doxcyline
(mild moderate)
Ceftriaxone +
Azithromycin
(severe cases)
1st gen cephalopsporin +
Doxcycline
Endocarditis Ampicillin +
Gentamicin
(SBE)
Flucloxacillin
(BE)
Vancomycin
Intra-abdominal infections Augmentin Ampicillin +
Gentamicin +
Metronidazole
(‘triple antibiotics’)
Cephazolin + Gentamicin +
Metronidazole
UTI Ampicilllin Ampicillin +
Gentamicin
Cephalexin (mild)
Ceftriaxone (severe)
PID (STD) Cetriaxone IM once stat +
Azithromycin
Ceftriaxone +
Azithromycin
Skin / MSK Flucloxacillin Flucloxacillin 1st gen cephalosporin
OR
Clindamycin

Antibiotic spectra – simplified

BACTERIAL CLASS TYPICAL ORGANISM TYPICAL ANTIBIOTIC OTHER ORGANISM SPECIAL ANTIBIOTIC
Gram +ve Strep
Staph
1st  gen cephalosporin
Flucloxacillin
‘Enterococcus’ – Strep faecalis
MRSA
Ampicillin
Vancomycin
Gram -ve Various Gentamicin Pseudomonas Piperacillin
Ciprofloxacin
Cefotaxime
Anaerobe Various Metronidazole
Clindamycin
Clostridia Penicillin

Pencillin classification – simplified

  Examples Spectra
Standard Phenoxypenicillin (Pen G) PO
Benzylpenicillin (Pen V) IV
Gram +ve
(some Gram -ve)
Extended cover Ampicillin / Amoxycillin /Augmentin More Gram -ve
Enterococcus
Anti-staph Flucloxacillin Staph. aureus
Anti-pseudomonal Ticarcillin
Piperacillin
Pseudomonas

Cephalosporin classification – simplified

Generation Examples Spectra
1st Cephalexin PO
Cephazolin IV
Gram +ve
(some Gram -ve)
2nd Cefaclor PO
Cefotetan IV
More Gram -ve
3rd Ceftriaxone Extended Gram -ve
Antipseudomonal Cefepime Pseudomonas

* No cephalosporin is active against enterococcus
Adult Antibiotic doses (typical – consult Therapeutic guidelines)

  250MG 300mg 500mg 1g 1.2g 1.5g
Daily Trimethoprim
Roxithromycin
Ceftriaxone
(2g bd in meningitis)
Azithromycin
 
BD Cephalexin  (for UTI) Vancomycin
TDS Ampicillin PO/IV
Erythtromycin IV
Metronidazole IV
Cephazolin
Cefotaxime
QID Erythromycin PO Cephalexin
Pencillin/Flucloxacillin PO
Flucloxacillin PO Pencillin IV

 

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