Intravitreal Toxicity of Doxycycline

Abstract

Abstract: : Purpose: To assess the retinal toxicity of varying concentrations of intravitreally administrated doxycycline, a member of the tetracycline family. Methods: Fourteen New Zealand albino rabbits used for this study were treated in accordance with the ARVO statement on the use of animals for ophthalmic and visual research. The anesthetized animals were divided into 7 groups. The initial concentration of doxycycline (100 mg) was titrated using 5% dextrose solution to the following concentrations: 2000 µg/0.1 ml, 1000 µg/0.1ml, 500 µg/0.1 ml, 250 µg/0.1 ml, 125 µg/0.1 ml, and 67.5 µg/0.1 ml which were injected intravitreally into one eye of each of 2 rabbits. Two control eyes received 0.1 ml of 5% dextrose solution. All animals were examined before and after injection using the indirect ophthalmoscope and slit–lamp biomicroscopy. Electroretinography (ERG) was performed on all animals prior to intravitreal injection and 2 weeks after injection. The animals were euthanized and their eyes were enucleated and examined with light microscopy. Results: The doxycycline group exhibited significant decreases in ERG of the eyes injected with 2000 µg/0.1 ml, 1000 µg/0.1 ml, 500 µg/0.1 ml, and 250 µg/0.1 ml. No significant changes were observed on ERG in eyes injected with lower concentration levels of doxycycline. There were no signs of retinal toxicity on slit–lamp examination, indirect ophthalmoscopy, or light microscopy in any of the eyes injected with doxycycline concentrations of 125 µg/0.1 ml or less. Conclusions: Intravitreal injections of doxycycline at concentrations of 125 µg/0.1 ml or less appeared to be nontoxic to the retina in albino rabbits; intravitreal doxycycline may be a beneficial and low–cost alternative drug in the treatment of bacterial endophthalmitis, particularly against resistant strains of Staphylococcus aureus.

Keywords: antibiotics/antifungals/antiparasitics • drug toxicity/drug effects • endophthalmitis