WHAT DOES “I” (INCREASED EXPOSURE/DOSE) MEAN ON MICROBIOLOGY REPORTS? (Antimicrobial)
TAM (Treatments and Medicines) NHS Highland
What's new / Latest updates
31/08/23 - A recent audit of ciprofloxacin dosing showed the recommended increased doses were not being prescribed in most cases. A questionnaire revealed prescribers were unaware and unfamiliar with the existing guidance on TAM and requested more detailed content. The title is now “What does “I” (increased exposure/dose) mean on Microbiology reports?” as it is more instructive. Some examples of translating the guidance into clinical practice are given to support optimal prescribing.
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.
|
S |
Susceptible at standard dose |
|
I |
Susceptible, increased exposure (= increased dose) |
|
R |
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.
|
Drug |
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 |
|
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 |