Successful use of intravitreal and systemic colistin in treating multidrug resistant Pseudomonas aeruginosa post-operative endophthalmitis

Dear Editor, We read with a great interest the article entitled “successful use of intravitreal and systemic colistin in treating multidrug resistant Pseudomonas aeruginosa postoperative endophthalmitis” by Samant and Ramugade.[1] They explored the efficacy of intravitreal and intravenous colistin in postoperative endophthalmitis; however, there are some points to be cleared out. First, the dose of intravitreal dexamethasone in the study was 10-fold greater than the recommended dose regimen. Second, there are no safety studies of colistin when given intravitreally; therefore, there is no determined safe intravitreal dose of colistin. Third, it has been reported that colistin did not reach therapeutically relevant levels in the aqueous and in the vitreous humor of rabbit eyes.[2] We wonder why the authors used such a high concentration of dexamethasone. The intravitreal dexamethasone dose should be 0.4 mg/0.1 ml instead of 4 mg/0.1 ml.[3] It would be informative if the authors explained how they found the dose of intravitreal colistin as 0.1 mg/0.1 ml. Finally, we argue that there should be a limited role for intravenously administered colistin in the treatment of Gram-negative bacterial endophthalmitis.