Interpreting Sensitivity Results

In line with new European reporting requirements, the Microbiology laboratory report susceptibility results in three categories: S, DS (or I) and R.

For some bug-drug combinations, there is no "S" category. Susceptibilities will be reported as either "DS" (or "I") or R.

  • "S" = susceptible at a standard dosing regimen.
    This means there is high likelihood of therapeutic success using standard doses and dosing intervals.
  • "DS" or "I" = Dose-dependent susceptible.
    This means there is high likelihood of therapeutic success if antibiotic exposure is optimised by using higher doses or increasing dosing frequency.
  • "R" = resistant. 
    This means there is high likelihood of therapeutic failure using this antibiotic.

For paediatrics where susceptibilities are reported as "DS" (or I) and a dosing range is given in the BNFc, the dose at the higher end of the range should be used. 

Please see below table for recommended doses and frequency for organisms with “DS” or "I" susceptibility.

Recommended doses for “DS” or "I" (Dose-dependent susceptible) organisms

These doses are for adults with normal renal function. For patients with renal impairment, use the maximum safe doses for the patient’s CrCl, discussing with a pharmacist if necessary.

Recommended doses for “DS” or "I" (Dose-dependent susceptible) organisms

​Organism

​Drug and Dose

​Dosing interval  

​ E.coli , Proteus mirabilis,  Klebsiella pneumoniae  and other coliforms (Enterobacterales group)

​Cefuroxime 1.5g IV

​Three times a day

​ Pseudomonas aeruginosa

​Piperacillin tazobactam 4.5g IV 

Ceftazidime 2g IV

Aztreonam 2g IV

Ciprofloxacin 750mg PO

Ciprofloxacin 400mg IV

​Four times a
day
Three times a
day
Four times a
day
Twice a day
Three times a day

​

Streptococci groups A, C and G And Streptococcus pneumoniae

 

 

​Levofloxacin 500mg PO/IV

​Twice a day

​Staphylococcus aureus

​Ciprofloxacin 750mg PO

Ciprofloxacin 400mg IV

 

Clindamycin 450-600mg PO

Clindamycin 600-1200mg IV

​Twice a day

Three times a day

 

Four times a day

Four times a day

​Haemophilus influenzae

​Amoxicillin 1g TDS PO

Amoxicillin 2g TDS IV

 

Co-amoxiclav 625mg PO prescribed with

Amoxicillin 500mg PO

 

Co-amoxiclav 1.2g IV
prescribed with  Amoxicillin 1g IV

​Three times a day

Three times a day

 

Three times a day

 

 

Three times a day

·         "R" = resistant.
This means there is a high likelihood of therapeutic failure using this antibiotic.

For paediatrics where susceptibilities are reported as "I" and a dosing range is given in the BNFc, the dose at the higher end of the range should be used.