Chemical parameters, antimicrobial activities, and tissue toxicity of 0.1 and 0.5% sodium hypochlorite solutions

The chemical parameters, antimicrobial activity, and tissue toxicity of two sodium hypochlorite (NaOCl) solutions buffered to a physiologic pH were studied. Initially, a 0.5% NaOCl solution buffered with 3 g of NaH₂PO₄ per liter was examined. The solution had a pH of 7.49 and an osmolality of 352 mOsmol/liter. When compared with unbuffered and NaHCO₃-buffered 0.5% NaOCl solutions, the NaH₂PO₄-buffered solution was significantly more effective in killing Staphylococcus aureus in vitro. However, the pH of the NaH₂PO₄-buffered solution decreased over time with a concomitant decrease in antibacterial activity. A freshly prepared solution decontaminated human cadaveric skin colonized by S. aureus, Pseudomonas aeruginosa, or Candida albicans in vitro within 10 min of exposure, whereas a 24-h-old solution cleared the skin of organisms within 15 min. When gauze soaked with 0.5% NaOCl was applied to guinea pig skin for 2 weeks, a 15% decrease in basal cell viabilities was noted. Because of the pH instability and basal cell toxicity, a 0.1% NaOCl solution buffered with NaH₂PO₄-Na₂HPO₄ was evaluated. This solution had an osmolality of 386 mOsmol/liter and a pH of 7.4 that was stable over 1 week. A freshly prepared 0.1% NaOCl solution decontaminated skin colonized with S. aureus, C. albicans, and P. aeruginosa within 10, 20, and 30 min, respectively. A 24-h-old solution did not completely decontaminate the colonized skin but significantly reduced the number of microorganisms on the skin surface (P < 0.001). Application of this solution to guinea pig skin for 2 weeks produced no significant effect on basal cell viabilities. These solutions may serve as alternative topical agents for use in burn therapy.