Dilute Povidone-Iodine Irrigation: The Science of Molecular Iodine (I2) Kinetics and Its Antimicrobial Activity

Dilute povidone-iodine (polyvinylpyrrolidone iodine [PVP-I]) irrigation in spine surgery and total joint arthroplasty has seen a rapid and substantial increase in its use during the past decade. Yet, most surgeons do not know the chemistry and biochemistry that explain its efficacy in preventing infections. PVP-I forms a complex with molecular iodine (I2), facilitating the delivery of I2 to the membrane of the infectious organism. Here, PVP-I establishes an equilibrium between complexed and noncomplexed (free) I2 in the aqueous solution. The I2 acts at numerous cellular targets of infecting organisms augmenting its role as a biocidal molecule. The paradoxical increase in the concentration of I2 that occurs with dilution of PVP-I is a result of equilibrium kinetics and is associated with an enhanced antimicrobial activity. Cytotoxicity studies have yielded conflicting results, but most endorse diluted concentrations as being less damaging to tissues. Clinical studies have verified notable reductions in surgical site infections with a 3-minute soak of 0.35% dilute povidone-iodine irrigation. Guidelines from the World Health Organization, Centers for Disease Control and Prevention, and International Consensus Meeting on Musculoskeletal Infection support the use of prophylactic incisional wound irrigation with aqueous PVP-I to reduce and prevent surgical site infections.