Five percent Povidone Iodine prior to ocular surgery good enough for Infection prevention: Study
Endophthalmitis after intravitreal injection is a rare but severe complication. Unlike endophthalmitis after cataract surgery, each patient has multiple chances of intraocular infection. Patients often require monthly injections of anti-vascular endothelial growth factor (VEGF) to control age-related macular degeneration (AMD), diabetic macular edema (DME), and retinal vein occlusion (RVO). Even oral flora spread through speech has been implicated as a vector for intraocular infection.
Ophthalmologists have turned to antiseptics instead of antibiotics for surgical prophylaxis, which includes intravitreal prophylaxis, because of the potential of acquired resistance due to frequent antibiotic application. The prophylaxis consensus prior to intravitreal injection and other ocular surgeries is the application of the antiseptic, 5% povidone iodine (PI), to the ocular surface and the clearance of the eyelid and lashes from the injection site.
PI is a composite of elemental iodine, hydrogen iodine, and povidone. It is an antibacterial broad-spectrum, in which free iodine is the active component, and it has minimal residual activity. It can be an irritant when left on tissue surfaces for a long time. The stinging and burning nature of 5% PI has prompted retinal specialists, especially in cases of multiple intravitreal injections, and other ocular surgeons to seek other effective prophylactic measures.
The present unique study by Kowalski et al utilized corneoscleral tissue to evaluate antiseptic susceptibility on a solid phase medium.
"The corneoscleral tissue would be a better reality assimilation of the ocular surface than bacterial dispersion in a liquid medium. The antiseptics would be tested against a panel of bacterial endophthalmitis isolates. The design of the study was to eliminate bacteria and not demonstrate a reduction, because dead bacteria do not cause infection. We hypothesize that 5% PI, 2.5% PI and HOCl will prevent equally bacterial growth within the recommended time frame of 3 minutes. Analysis will include a projected weighted comparison over a 27-year period."
Bacteria from 20 cases of endophthalmitis were tested for the elimination of growth against topical 5% PI, 2.5% PI, HOCl, and no antiseptic using donor corneoscleral tissue.
The tissue was inoculated with 103 colony forming units of bacteria prior to a 3-minute contact time with the antiseptics, placed in liquid growth medium, and monitored for growth at three days. No growth indicated antiseptic treatment success.
- For 20 isolates, 5% PI was comparable to 2.5% PI for preventing bacteria growth (p=0.71), and both were more effective than HOCl (p=0.004).
- Estimated weighted comparison over a 27-year period indicated that for all bacterial groups, except Streptococcus viridans, 5% PI was equally effective to 2.5% PI for preventing bacterial growth (p=1.0).
- For Streptococcus viridans, 5% PI was more effective than 2.5% PI (p=0.0001).
- Both concentrations of PI were more effective than HOCl (p=0.00001)
Antibiotic susceptibility testing for systemic treatment is based on the concentrations of antibiotic in the blood serum. There are no standards for topical treatment or intravitreal injection. Testing is performed in liquid medium with varying concentrations of antibiotic to determine an inhibitory concentration and not a bactericidal concentration. This dispersion of bacteria in antibiotic supplemented medium requires 24 hours of incubation time. This indirect approach is cost-effective and is the standard to estimate in vitro to in vivo correlation in a timely manner, but this does not necessarily represent the true reality of treatment. A more accurate approach to test susceptibility would be to use a solid medium to simulate an infection in tissue (ie skin, cornea). The anti-infective would be applied to the tissue with attached bacteria at different time frames to determine efficacy of treatment.
Endophthalmitis after intravitreal injection is a rare event, but the data indicates the best antiseptic to prevent infection is 5% PI. Except for Sv, 2.5% PI was just as effective as 5% PI. HOCl was less effective as an antiseptic to prevent bacterial growth in the present study, but HOCl may provide prophylaxis in those that are allergic to PI.
It appears that both PI and HOCl have less activity to the Streptococci groups and Bacillus species that have cell wall components that inactivate free iodine and resist oxidation. Authors rejected the original hypothesis because both 5% PI and 2.5% PI were more effective than HOCl for preventing bacterial growth from corneoscleral tissue. This model should be considered to evaluate other anti-infectives for preventing bacterial growth on ocular tissues.
Source: Kowalski et al; Clinical Ophthalmology 2021:15 3697–3704
