Topical Losartan Dosage Response and Corneal Toxicity at Higher Concentrations

The purpose of this study was to evaluate the efficacy and safety of higher dosages of topical losartan in an alkali-burn fibrosis model in rabbits.

In total, 18 rabbits had standardized alkali burns that trigger stromal fibrosis. Six eyes per group were treated with topical losartan (0.8 mg/mL, 8 mg/mL, or 40 mg/mL) 6 times per day. Slit-lamp photographs were obtained, and multiplex immunohistochemistry was performed for myofibroblast marker alpha-smooth muscle actin (α-SMA), mesenchymal cell marker vimentin, and basement membrane marker laminin alpha-5.

Topical losartan at 40 mg/mL 6 times per day produced severe discomfort and ocular surface toxicity in all rabbits, and treatment was discontinued at nine days in this group. Topical losartan at 8 mg/mL 6 times per day caused less rabbit discomfort on application, but there were persistent epithelial defects and marked stromal opacity in 5 of 6 eyes after 1 month of treatment. Topical losartan 0.8 mg/mL was well tolerated by rabbits, and corneal opacity was markedly reduced at 1 month in 5 of 6 corneas compared with corneas in the 8 mg/mL and 40 mg/mL losartan groups. A persistent epithelial defect with opacity was noted in 1 cornea in the 0.8 mg/mL losartan group. Both total SMA-positive stromal cells per section (14.5 ± 2.8 vs. 3.5 ± 0.7, P = 0.04) and total stromal vimentin intensity units (310 ± 64 vs. 132 ± 35, P = 0.02) were significantly greater after 1 month of treatment in corneas treated with 8 mg/mL than corneas treated with 0.8 mg/mL of topical losartan.

Topical losartan dosages over 0.8 mg/mL should be used cautiously in patient eyes. In eyes with a current epithelial defect, it is recommended that 0.2 mg/mL losartan 6 times per day be used until the epithelium closes.