Interpreting Sensitivity Results

This guidance is for health professionals only.

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.

 

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.

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.

 

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

Drug and dosage:

  • Cefuroxime 1.5g IV, three times a day.

 

Pseudomonas aeruginosa

Drug and dosage:

  • Piperacillin tazobactam 4.5g IV, four times a day
  • Ceftazidime 2g IV, three times a day
  • Aztreonam 2g IV, four times a day
  • Ciprofloxacin 750mg PO, twice a day
  • Ciprofloxacin 400mg IV, three times a day.

 

Streptococci groups A, C and G, and Streptococcus pneumoniae

Drug and dosage:

  • Levofloxacin 500mg PO/IV, twice a day.

 

Staphylococcus aureus

Drug and dosage:

  • Ciprofloxacin 750mg PO, twice a day
  • Ciprofloxacin 400mg IV, three times a day
  • Clindamycin 450-600mg PO, four times a day
  • Clindamycin 600-1200mg IV, four times a day.

 

Haemophilus influenzae

Drug and dosage:

  • Amoxicillin 1g TDS PO, three times a day
  • Co-amoxiclav 625mg PO prescribed with Amoxicillin 500mg PO, three times a day.

Contact Microbiology

Call 01623 622515, extension 3630, between 9am to 5pm Monday to Friday.

Out-of-hours to contact the duty Microbiologist on-call.