Rapid degradation and non-selectivity of Dakin's solution prevents effectiveness in contaminated musculoskeletal wound models

Background: Dakin's solution (buffered sodium hypochlorite) has been used as a topical adjunct for the treatment of invasive fungal infections in trauma patients. Prudent use of Dakin's solution (DS) for complex musculoskeletal wound management implies balancing antimicrobial efficacy and human tissue toxicity, but little empirical evidence exists to inform clinical practice. To identify potentially efficacious DS concentrations and application methods, we conducted two animal studies to evaluate the ability of DS to reduce bacterial burden in small and large animal models of contaminated musculoskeletal wounds. Methods: An established rat (Rattus norvegicus) contaminated femoral defect model was employed to evaluate the antimicrobial efficacy of DS as a topical adjunctive treatment for Staphylococcus aureus infection. A range of clinically-relevant DS concentrations (0.00025%–0.125%) were tested, both with and without periodic replenishment during treatment. Next, an established goat (Capra hircus) musculoskeletal wound model, consisting of a Pseudomonas aeruginosa contaminated proximal tibia cortical defect, muscle crush, and thermal injury, was utilized to evaluate the antimicrobial efficacy of dilute DS (0.0025% and 0.025%) as a surgical irrigant solution. In situ reactive chlorine concentrations were monitored throughout each treatment using an automated iodometric titration approach. Results: In a rat wound model, DS treatment did not significantly reduce S. aureus bioburden after 14 days as compared to saline control. Two treatment groups (0.01% single application and 0.025% multiple application) exhibited significantly higher bacterial burden than control. In a goat musculoskeletal wound model, neither 0.0025% nor 0.025% DS significantly altered P. aeruginosa bioburden immediately following treatment or at 48 h post-treatment. Overall, DS applied to exposed soft tissue exhibited rapid degradation, e.g., 0.125% DS degraded 32% after 5 s progressing to 86% degradation after 15 min following single application. Conclusions: We did not observe evidence of a therapeutic benefit following Dakin's solution treatment for any tested concentration or application method in two contaminated musculoskeletal wound models. Despite confirmation of robust bactericidal activity in vitro, our findings suggest DS at current clinically-used concentrations does not kill tissue surface-attached bacteria, nor does it necessarily cause host tissue toxicity that exacerbates infection in the setting of complex musculoskeletal injury.