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A. Chen, L. Prajna, M. Srinivasan, N. Acharya, T. Lietman; Does in vitro Susceptibility Testing Predict Clinical Outcomes in Bacterial Keratitis? -Results From the Steroids for Corneal Ulcers Trial (SCUT) Pilot Study. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4277.
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Minimal inhibitory concentrations (MIC’s) are routinely measured for infectious keratitis to determine the susceptibility of inciting organisms to specific agents. However, there are limited data on whether the in vitro antibiotic susceptibility is associated with clinical outcomes in vivo.
A randomized, double-masked clinical trial was conducted at the Aravind Eye Hospital Cornea Clinic in Madurai, India to assess the effect of topical corticosteroid treatment on bacterial corneal ulcers. Forty-two patients with culture-confirmed bacterial keratitis were randomized to steroid and placebo groups. All study patients were to receive topical moxifloxacin treatment, although physicians were permitted to add or change antibiotics if necessary. Best-corrected visual acuity and infiltrate-scar size were measured. An average MIC for moxifloxacin was obtained from tests run on two separate days for each bacterial isolate using Etests. Statistical analyses were performed using multiple linear regressions.
A multiple linear regression model correcting for infiltrate-scar size at enrollment showed that every two-fold dilution in MIC level was associated with a 0.25 mm increase in infiltrate-scar size at 3 weeks (P=0.052) and associated with a 0.32mm increase at 3 months (P=0.03). No significant association was observed between MIC and logMAR visual acuity at 3 weeks (P= 0.52) or 3 months (P=0.95). Moxifloxacin E-test reproducibility was high (intra-class correlation was 0.94).
A higher MIC is associated with a larger final infiltrate-scar size but not visual acuity. Limitations of this study include a modest sample size.
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