Safety of intrastromal injection of polyhexamethylene biguanide and propamidine isethionate in a rabbit model

Acanthamoeba keratitis (AK) is difficult to treat, especially when the corneal deep stroma is involved. Intrastromal injection of antimicrobial agents is an effective adjuvant therapy for deep recalcitrant microbial keratitis; however, it has not been used to treat AK due to suspected drug toxicity. The purpose of this study was to evaluate the toxicity of corneal intrastromal injection of polyhexamethylene biguanide (PHMB) and propamidine isethionate (Brolene®, Sanofi) in New Zealand white rabbits. We performed intrastromal injections of PHMB (0.02 or 0.01%) and propamidine isethionate (0.1 or 0.05%) into the rabbits’ right corneas. The left corneas were injected with phosphate-buffered saline as controls. The rabbits were sacrificed on the 7th day after injection, and the corneal buttons were harvested for further evaluation by slit lamp microscopy, specular microscopy, hematoxylin and eosin staining, scanning electron microscopy, terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling assays, and WST-1 assays. We found that intrastromal injection of 0.02% PHMB or 0.1% propamidine isethionate resulted in corneal epithelial erosion, corneal edema, and severe neovascularization. However, 0.01% PHMB or 0.05% propamidine isethionate did not induce obvious cornea toxicity. In conclusion, intrastromal injection of 0.01% PHMB or 0.05% propamidine isethionate may be promising adjunctive treatments for deep stromal AK.