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Effects of intravitreal dexamethasone on concentration of intravitreal vancomycin in experimental
M A Smith1, J A Sorenson, C Smith
1Department of Medicine, Long Island Jewish Medical Center, New Hyde Park, New York 11042.
Abstract:
Intravitreal corticosteroids in the treatment of bacterial endophthalmitis remain controversial. We utilized an experimental rabbit model of methicillin-resistant Staphylococcus epidermidis endophthalmitis (i) to calculate the intravitreal vancomycin concentration in rabbit eyes receiving intravitreal vancomycin alone or in combination with intravitreal dexamethasone and (ii) to determine whether an intravitreal steroid has any effect on intravitreal vancomycin levels. All right eyes were infected and all left eyes were uninfected. The rabbits were divided into two treatment groups: (i) 32 eyes (group I) were injected with intravitreal vancomycin, 1.0 mg (0.1 ml); (ii) 32 additional eyes (group II) were injected with intravitreal dexamethasone, 400 micrograms (0.1 ml), in addition to vancomycin. Measurement of intravitreal vancomycin concentration was performed following sacrifice, utilizing a microbiologic agar diffusion assay. Analyses of intravitreal vancomycin concentrations were performed by using model-independent parameters, with area under the concentration-time curves derived by trapezoidal approximation. The intravitreal vancomycin concentration was significantly lower in both uninfected and infected group II eyes (P less than 0.002). Analysis of intravitreal vancomycin concentration-time relationships was performed by using a nonlinear least-squares regression program; data best fit a one-compartment model. In addition, no vancomycin-dexamethasone interaction could be demonstrated. The reduced level of intravitreal vancomycin in the presence of intravitreal dexamethasone may have important clinical implications.
Insights
Intravitreal corticosteroids reduce vancomycin levels in rabbit eyes with bacterial endophthalmitis. This study investigated the impact of intravitreal dexamethasone on vancomycin concentrations during treatment for methicillin-resistant Staphylococcus epidermidis endophthalmitis.
Area of Science:
- Ophthalmology
- Infectious Diseases
- Pharmacology
Background:
- Intravitreal corticosteroid use in bacterial endophthalmitis treatment is debated.
- Methicillin-resistant Staphylococcus epidermidis (MRSE) poses a significant treatment challenge.
Purpose of the Study:
- To determine intravitreal vancomycin concentrations in a rabbit model of MRSE endophthalmitis.
- To assess the effect of intravitreal dexamethasone on vancomycin levels.
Main Methods:
- Experimental rabbit model of MRSE endophthalmitis.
- Intravitreal vancomycin administered alone or with dexamethasone.
- Microbiologic agar diffusion assay for vancomycin concentration measurement.
Main Results:
- Intravitreal vancomycin concentrations were significantly lower in eyes receiving dexamethasone (P < 0.002).
- Data fit a one-compartment model, with no direct vancomycin-dexamethasone interaction identified.
- Reduced vancomycin levels in the presence of dexamethasone were observed in both infected and uninfected eyes.
Conclusions:
- Concomitant intravitreal dexamethasone administration may reduce therapeutic vancomycin levels in bacterial endophthalmitis.
- Findings suggest potential clinical implications for combination therapy regimens.
- Further research is warranted to optimize treatment strategies.