Abstract
Purpose :
The use of lidocaine gel was reported as a potential independent risk factor in the development of post-intravitreal injection endophthalmitis. Previously, we reported that 10% povidone-iodine (PVI) swabs were able to penetrate lidocaine gel to yield comparable PVI concentration to 5% PVI solution without gel. This follow up study aimed to directly determine the bactericidal effectiveness of various PVI applications by demonstrating growth inhibition of Staphylococcus epidermidis.
Methods :
Mueller Hinton agar plates were inoculated with S. epidermidis (ATCC 12228) from a tryptic soy agar slant. 6mm diameter discs were punched from cellulose filter paper. In the control group, 50 µL of 5% PVI was applied to the discs. 5 variable groups were treated with (1) 3.5% lidocaine gel plus 50 µL 5% PVI, (2) gel with 10% McKesson PVI swab, (3) gel with 10% PDI PVI swab, (4) gel with 5% PVI soaked cotton-tip applicator (CTA), and (5) gel with 10% soaked CTA. An additional plate with a plain disc, disc with lidocaine gel, and PDI PVI 10% swab directly applied served as controls. The discs were placed on the inoculated plates and incubated for 24 hours. Zones of inhibition (ZOI) were measured for each plate.
Results :
10 discs were plated for each group. The gel + 5%, gel + McKesson swab, gel + 5% CTA, and gel + 10% CTA groups yielded smaller ZOIs compared to the control, no gel + 5% (all p<0.001), and to gel + 10% PDI swab (all p <0.001). There was no significant difference between the ZOI of the control versus gel + 10% PDI swab. Both Mckesson and PDI swabs yielded a greater ZOI than gel + 5% (p<0.001), however PDI swabs produced a greater ZOI than McKesson swabs (p=0.0004).
Conclusions :
The results redemonstrated that the gel barrier significantly decreases the amount of 5% PVI solution in contact with the treated surface. The data suggests that the mechanical force of application with 10% PVI swabs can penetrate the gel barrier with enough PVI to produce a bactericidal effect similar to the control. However, the amount of PVI is dependent on the manufacturer and amount of PVI loaded into the swab.
The main limitation of this study lies in its in vitro nature. Major differences between our model and the human eye may affect interaction with topical PVI. Further investigation with randomized controlled trials are needed to elucidate the relationship between post-injection endophthalmitis and prep method.
This is a 2021 ARVO Annual Meeting abstract.