Povidone-Iodine in Ophthalmic Surgery
Postoperative endophthalmitis is a greatly feared surgical complication for all ophthalmologists.
Historically, many different methods have been employed in an attempt to reduce this risk, including sterile surgical technique and postoperative use of topical antibiotics. Despite the wide-spread use of postoperative antibiotic drops in clinical practice, cleaning of the surgical site with povidone-iodine is the only technique scientifically proven to reduce the risk of endophthalmitis after intraocular surgeries.
Prior to povidone-iodine, a mild silver protein (Argyrol) was commonly used to sterilize the surgical field; however, its use was discontinued after a 1983 study showed that Argyrol had little bactericidal effect. A randomized control study performed at New York Eye and Ear Infirmary in 1991 confirmed that preoperative application of povidone-iodine, as compared to silver protein solution, decreased the rate of post-operative endophthalmitis after intraocular surgery.Based on the results of these studies, povidone-iodine quickly replaced other agents and became the most wide-spread agent in preparing the surgical field.
Long before the development of povidone-iodine in the 1950’s, many other iodophers were sold and marketed for their disinfectant properties. Iodine in its elemental form has intrinsic bactericidal properties; however, its insolubility in water and high toxicity limits its use. In 1830, “tincture of iodine” was developed as a solution of 5% elemental iodine and 10% potassium iodine to overcome some of these disadvantages. When povidone-iodone, a unique formulation of Polyvinylpyrrolidone (povidone) and elemental iodine, was introduced to the antiseptic market in the 1950’s, it was coined “tamed iodine” for its improved safety profile. By complexing povidone with iodine, the toxicity was significantly decreased and the solubility dramatically increased. Most importantly, this was all done without decreasing its germicidal activity.
Mechanism of action
Polyvinylpyrrolidone alone does not have any bactericidal properties, but its natural affinity to bacterial cell membranes indirectly increases iodine’s antimicrobial nature by delivering the active agent to its intended target. The free iodine in solution binds to saturated fatty acids in the cell membrane and substitutes for covalently bound hydrogen ions, leading to pore formation in the cell wall and inducing bacterial cell death. In-vitro studies demonstrate that the amount of free molecular iodine increases when povidone-iodine is diluted with solvent, and then subsequently decreases with further dilution. One hypothesis to why this bell-shaped phenomenon occurs is that polymeric aggregates entrap free iodine when little solvent is present, making them inaccessible to the bacterial cell wall. Upon initial dilution with solvent, these aggregates will dissolve and increase the availability of free iodine. The ideal concentration of povidone-iodine has yet to be determined for clinical practice; however, a study done in 2003 demonstrated the bactericidal effect of 5% povidone-iodine to be superior to 1% povidone-iodine in cataract surgery patients. 
- Low cost
- Rapid and broad-spectrum anti-microbial
- Low toxicity
- High water solubility
- Absence of microbial resistance
- Ease of application and storage
Povidone-iodine has been extensively studied, and its bactericidal activity has been demonstrated in numerous clinical studies. Specific in-vivo studies done on the ocular surface have shown a 96.7% kill rate within 60 seconds, confirming its utility in preoperative preparation for ophthalmologic surgeries. Additionally, there has been no reported microbial resistance to povidone-iodine, making it a revolutionary and critical component in reducing surgical site infections.
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