Comparison of neutralization and disinfection kinetics in povidone iodine‐ and hydrogen peroxide‐based soft contact lens care solutions
Charles Bahr, Megumi Kitamura, Haruki Nakagawa, Kazuhiro Sasanuma, Katsuhide Yamasaki, Fumio SaitohABSTRACT
Purpose
To assess and compare the time‐dependent disinfection efficacy against standard microbial strains and the neutralization kinetics of two commercially available soft contact lens care systems, one based on 0.05% povidone iodine and one based on 3.42% hydrogen peroxide.
Methods
To assess neutralization kinetics of each system, the concentration of the active disinfectants was quantified via iodometric titration (hydrogen peroxide) and high‐performance liquid chromatography (povidone iodine) at intervals from 0.5 min to the minimum recommended disinfection time (MRDT). Disinfecting efficacy against the five ISO 14729 microbial strains ( Pseudomonas aeruginosa , Serratia marcescens , Staphylococcus aureus , Candida albicans , Fusarium solani ) was assessed at intervals from 0.5 min to each system's respective MRDT. Microbial log reductions and disinfection rates were calculated using standard plate count methods. Statistical significance between systems was determined using ANOVA and post‐hoc comparisons ( p < 0.05).
Results
The povidone iodine system reached a peak concentration (∼0.05%) within 2 min, maintained this level for 5 min, and was neutralized by 20 min. Despite rapid neutralization, povidone iodine exceeded the standardized criteria for all strains within 1 min and disinfected below the detectable limit within 5 min. Conversely, the hydrogen peroxide system's concentration began declining immediately and fell below 1% within 30 min, before disinfection was complete for three strains. Significant kinetic differences ( p < 0.05) favored povidone iodine across four strains, most notably against S. aureus , where hydrogen peroxide lagged by several hours.
Conclusions
This study possesses a conflict of interest, and external validation is encouraged. The povidone iodine system achieved remarkably rapid disinfection across all strains at a 5000‐fold lower molar concentration than the hydrogen peroxide system, well below the ocular irritation threshold. Povidone iodine's consistent, rapid disinfection, along with its high safety profile, suggests it may be a more optimal care option than the current gold standard.