Suspected necrotising fasciitis or severe or rapidly progressing infection in IVDU


Mixed organisms including anaerobes


Seek advice from ID/micro

First Line

IV Flucloxacillin5 2g 6 hourly

+ IV Benzylpenicillin5 2.4g 4 hourly

+ IV Gentamicin3

+ IV Clindamycin 900mg 8 hourly

+ IV Metronidazole 500mg 8 hourly

Penicillin Allergy

Omit flucloxacillin and benzylpenicillin


Consider early debridement/ exploration and involve microbiologist


Doses may need to be adjusted in renal impairment. Always check BNF for interactions. Seek advice if patient pregnant

Drug specific cautions:

  1. Check interactions in the BNF. Caution may prolong QT interval.
  2. Avoid Doxycycline and Co-trimoxazole if pregnant or breast feeding
  3. Gentamicin/Vancomycin refer to online calculators
  4. ALERT antibiotic needs ALERT form
  5. Monitor sodium
  6. See CURB65 definition
  7. Reference: The Renal Drug Handbook 4th Edition, 2014