Laparoscopic Methylene Blue Photodynamic Therapy for Intraabdominal Infection: A Preclinical Feasibility Study in a Rabbit Model of Perforated Appendicitis

ABSTRACT Objectives Perforated appendicitis commonly results in intra‐abdominal infection requiring prolonged antibiotic therapy. Intraoperative antimicrobial adjuncts are limited, and photodynamic therapy (PDT) may provide a targeted, resistance‐independent approach. This study evaluated the feasibility, safety, and preliminary antimicrobial effects of laparoscopic methylene blue photodynamic therapy (MB‐PDT) for intra‐abdominal disinfection in a rabbit model of perforated appendicitis. Materials and Methods New Zealand White rabbits ( n = 19) underwent surgically induced perforated appendicitis via appendiceal ligation and electrocautery perforation. Animals subsequently received laparoscopic MB‐PDT ( n = 9) or control treatment (methylene blue lavage without laser illumination; n = 10) 24–40 h after perforation. MB‐PDT consisted of peritoneal lavage with methylene blue (300 µg/mL) followed by 665‐nm laser illumination at 20 mW/cm 2 to a fluence of 25 J/cm 2 . Peritoneal aspirates were obtained before and 24 h after intervention to quantify bacterial burden. In vitro PDT was evaluated in isolated organisms. Intraperitoneal organs were assessed histologically for off‐target effects. Primary outcomes were feasibility, safety, and in vivo change in bacterial burden. Secondary outcomes included clinical parameter changes and in vitro efficacy. Results Fourteen rabbits developed peritonitis, and 10 animals completed follow‐up (PDT n = 7, control n = 3). Laparoscopic MB‐PDT delivery was technically feasible and no histologic evidence of off‐target photodynamic injury to abdominal organs was identified. Changes in bacterial burden were not significantly different between MB‐PDT and control animals ( p = 0.18). Body temperature showed a non‐significant trend toward reduction following MB‐PDT (−0.37°C ± 1.32°C) compared with controls (0.26°C ± 0.76°C; p = 0.27). In vitro MB‐PDT produced significant reductions in bacterial burden across all isolated species ( p < 0.001), with the most resistant Gram‐positive isolate, Enterococcus faecalis , demonstrating greater susceptibility than Gram‐negative species. Conclusion Laparoscopic MB‐PDT was technically feasible and safe in a rabbit model of perforated appendicitis. Although a reduction in bacterial burden was not observed in vivo, MB‐PDT produced strong antimicrobial activity in vitro against all bacterial species isolated from infected animals. These findings establish a preclinical technical platform for intra‐abdominal MB‐PDT and highlight the importance of optimized light‐delivery strategies for future translational studies.