Povidone Iodine

Povidone iodine (7.5–10%) is mostly bactericidal in 30 s and yeasticidal in 2 min. Tuberculocidal activity can be found with 1% available iodine in 1 min. Its antimicrobial activity is explained by irreversible protein coagulation, metabolic inhibition and pore formation in the cell wall. No specific cellular defence mechanisms have been described. Its effect on biofilm formation is inconsistent. Existing biofilm may be moderately reduced (P. aeruginosa, S. aureus, C. albicans) or remain more or less unchanged (E. coli, E. faecalis, S. epidermidis, S. mutans). Elevated MIC values suggesting povidone iodine tolerance have been reported for L. lactis (≤30,000 mg/l), S. aureus and S. epidermidis (≤14,000 mg/l), P. aeruginosa (12,500 mg/l) and E. coli, K. pneumoniae and S. marcescens (all ≤10,000 mg/l), but their relevance is uncertain. Specific resistance mechanisms are unknown. Low-level exposure results in no MIC change in five species and a weak MIC change in isolates of two species (P. aeruginosa and S. aureus). A strong MIC change has not yet been described. Low-level exposure inhibited biofilm formation in S. aureus and S. epidermidis and increased the growth rate in P. aeruginosa. Cross-tolerance to other biocidal active substances or antibiotics has not been reported. Insufficient efficacy in suspension tests has occasionally been reported for culture collection strains of E. coli, E. faecium, E. hirae, S. aureus and S. epidermidis, although most studies describe sufficient bactericidal activity at the concentrations used. No povidone iodine-resistant isolates have been described with an insufficient efficacy in tests under practical conditions. Contaminated solutions or products based on povidone iodine have been associated with cases of peritonitis, bacteraemia or pseudo-bacteraemia caused by P. aeruginosa or P. cepacia. The overall probability of resistance to povidone iodine of practical relevance is low in the absence of biofilm.