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Reporting of antibiotic susceptibility from microbiology laboratories has changed in line with European recommendations.   Since June 2021, more antibiotics are reported as I as well as the more familiar S and R.   The definitions of these are listed below.


Susceptible at standard dose


Susceptible, increased exposure (= increased dose)


Resistant even with increased exposure/dose

Agents reported as “I” are still appropriate treatment options when given at the correct (higher) dose.   These higher doses are listed in the table below.  

If in doubt or antibiotic dose not listed below please discuss with clinical microbiologist. 


Increased Dose             

Benzylpenicillin IV

1.2g to 2.4g 4 to 6 hourly

Temocillin IV

2g 8 hourly

Piperacillin/tazobactam IV

4.5g 6 hourly

Ceftazidime IV

2g 8 hourly

Aztreonam IV

2g 6 hourly

Co-trimoxazole IV/Oral

1440mg 12 hourly

Amoxicillin Oral

1g 8 hourly

Co-amoxiclav Oral

Co-amoxiclav 625mg 8 hourly
+ Amoxicillin 500mg 8 hourly

Levofloxacin IV/Oral

500mg 12 hourly

Ciprofloxacin IV

400mg 8 hourly

Ciprofloxacin Oral

750mg 12 hourly

Please note these doses are applicable to dosing in adults with normal renal and hepatic function.   In impaired hepatic/renal function please adjust accordingly/discuss with pharmacist.

For information on dose changes for children, please see the advice from Scottish Antimicrobial Prescribing Group, Paediatric Stewardship Working Group.

Aminoglycoside sensitivity reporting has changed in line with EUCAST recommendations.  This does not affect clinical practice, provided patients are improving on therapy.

Some examples in practice:

Organism Antibiotic Result Dose
Pseudomonas aeruginosa Ciprofloxacin I: Use at increased dose Oral 750mg 12 hourly
IV 400mg 8 hourly
Piperacillin/tazobactam I: Use at increased dose IV 4.5g 6 hourly
Staphylococcus aureus Ciprofloxacin I: Use at increased dose Oral 750mg 12 hourly
IV 400mg 8 hourly
Levofloxacin I: Use at increased dose Oral/IV 500mg 12 hourly
Haemophilus influenzae (excluding meningitis) note: increased dose only applies to oral route Oral amoxicillin I: Use at increased dose Oral 1g 8 hourly
Oral co-amoxiclav I: Use at increased dose Oral co-amoxiclav 625mg 8 hourly PLUS oral amoxicillin 500mg 8 hourly

Last reviewed: 31/08/2023

Next review date: 31/08/2026

Version: 2

Approved By: TAM Subgroup of ADTC

Reviewer name(s): Alison Macdonald, Area Antimicrobial Pharmacist.

Document Id: AMT186