Abstract
Purpose::
To determine in microbial keratitis,• minimum inhibitory concentrations (MIC) of topical ophthalmic antimicrobials• if outcome is a function of the bacteria, antimicrobials and host,• ophthalmic breakpoints describing susceptibility & resistance for topical ophthalmic antimicrobials
Methods::
MIC were determined for 10 antimicrobials: ciprofloxacin (CIP), ofloxacin (OFL), ceftazidine (TZ), cefuroxime (XM), amikacin (AK), chloramphenicol (CHL), gentamicin (GM), penicillin G (PG), vancomycin (VM), teicoplanin (TP) against organisms isolated from corneal ulcers. Clinical outcome data such as ulcer and scar size, risk factors, healing (HT) and treatment times (TT) were collected.
Results::
1021 isolates from cases microbial keratitis were analysed: pneumococcus (4%), pseudomonas (22%), CNS (22%), staphylococcus aureus (16%) of which 11% MRSA, Gram -ve coccobacilli 4% (haemophilus 15%, neisseria 3%, moraxella 27%) other Gram -ve 16% (coliforms 87%), other Gram +ve 16%. 40% streptococcus sp. resistant to fluroquinolones (systemic break points), but sensitive to CHL., XM, TP. & PG. Clinical outcome data from 300 cases so far analysed. Mean ulcer size 2.8mmx2.1mm, scar size 1.7mmx1.3mm, risk factors 1.6, TT 27 (SD 31) days, HT 19 (SD 33) days. HT to area of ulcer 2.6. There was a significant association between HT, ulcer size and MIC for pseudomonas keratitis, that is, Outcome[PS,FL] ~ F{Pseudomonas, Fluoroquinolone, host} (p=0.012). Assuming equivalent concentrations in the cornea, antimicrobials were ranked in terms of their mean MIC plus 2 standard deviations as follows. Combination therapy: CIP+TP, OFL+TP, CIP+PG, CIP+XM, GM+PG, CIP+CHL. Monotherapy: CIP, OFL, GM, TZ CHL.
Conclusions::
There is an association between outcome and MIC of the antimicrobial (fluroquinolone) and bacteria (pseudomonas) in microbial keratitis. Initial monotherapy with a fluroquinolone is indicated with additional therapy to cover Gram +ve organisms, TP, PG or XM. The association for other bacteria and antimicrobials is under analysis.
Clinical Trial::
Audit Royal Liverpool University Hospital