A higher concentration of vancomycin for your methicillin-resistant Staphylococcus aureus (MRSA) keratitis patients may be more effective in eradicating symptoms, but lower concentrations administered over a longer duration may still result in improvements without ocular discomfort and better compliance, researchers from the University of Pittsburgh suggest.

Their study looked at the antibacterial effectiveness of vancomycin at 5%, 2.5% and 1.25%, in addition to saline, for the topical treatment of MRSA keratitis over an early, short-term course of treatment.

While topical vancomycin 5% (50mg/mL) is common to treat MRSA keratitis, some doctors opt to use lower concentrations due to patient comfort issues, the researchers noted in their paper on the study.

The study included 45 ulcerated rabbit corneas divided into three treatment groups (5%, 2.5%, and 1.25%), one untreated control group (saline) and an onset of therapy group (nine per group, three per trial). Both eyes of each rabbit of the treatment groups were treated with one 37mL drop of 50mg/mL (5%) vancomycin, 25mg/mL (2.5%) vancomycin, 12.5mg/mL (1.25%) vancomycin and saline. The corneas were treated every 15 minutes for five hours (21 total doses).

Ocular toxicity was concentration dependent from mild to moderate, the study noted. For the abraded corneas, the levels of MRSA in the vancomycin 5% group were lower than those in the 2.5% and 1.25% groups, and all vancomycin groups had lower MRSA levels than saline group. The investigators also reported the amount of MRSA in the 2.5% group was lower, yet similar, to the 1.25% group.

The vancomycin 5% group demonstrated a bactericidal effect and the best penetration, and the amount of MRSA in the abraded corneas treated with saline were lower than those of the intact corneas, indicating a possible antibacterial effect from the ocular surface, researchers said.

Still, the lower concentrations appeared to be active, and extended topical therapy (greater than five hours) may be comparable with vancomycin 5%, the investigators wrote.

Vancomycin is an appropriate choice at concentrations of 5% or 2.5%, and possibly 1.25%, to treat MRSA keratitis, the researchers wrote in their paper. Higher concentrations may be intolerable to the patient, and the clinician may need to reassess treatment regarding antibacterial efficacy and patient comfort, they added.

Romanowski EG, Romanowski JE, Shanks RMQ, et al. Topical vancomycin 5% is more efficacious than 2.5% and 1.25% for reducing viable methicillin-resistant staphylococcus aureus in infectious keratitis. Cornea. October 24, 2019. [Epub ahead of print].