Methylene blue photodynamic therapy for treatment of deep tissue abscess cavities (Conference Presentation)

Abstract

Deep tissue abscesses remain a significant cause of morbidity, mortality, and hospital stay despite improved surgical techniques and use of perioperative antibiotics. Long-term antibiotics increase risk of acquired resistance and polymicrobial infection, limiting future treatment options. We have therefore undertaken a Phase 1 clinical trial to evaluate safety and feasibility of methylene blue mediated photodynamic therapy (MB-PDT) at the time of drainage to treat deep tissue abscesses. This trial uses a fixed photosensitizer dose (1 mg/mL) delivered directly to the abscess cavity, and escalates light dose using a 3+3 design. Three patients were treated at the lowest light dose (20 mW/cm2, 6 J/cm2), with no study-related adverse events. Based on the technical success of this group, recruitment will continue for higher light dose groups with relaxed inclusion criteria. This trial restricts potential subjects to those with single abscesses less than 8 cm in diameter. To investigate MB-PDT feasibility in a wider population, we extracted CT images for patients receiving abscess drainage locally. Images were segmented and imported into a custom Monte Carlo simulation framework. Simulations were performed to determine whether 20 mW/cm2 could be delivered to 95% of the abscess wall, given the available 2 W of optical power at the treatment fiber output. Preliminary results show that this is achievable in 80% of abscesses examined, with volumes ranging from 30-250 mL. Optical power required ranged from 50-950 mW. Based on these initial results, it appears that a large number of abscesses drained may be candidates for MB-PDT.