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Summary

Background  With increasing problems of antibiotic resistance, photodynamic therapy (PDT) is being developed as a novel antimicrobial treatment. Following light activation, cationic photosensitizer PPA904 [3,7-bis(N,N-dibutylamino) phenothiazin-5-ium bromide] kills a broad spectrum of bacteria in vitro and this has a variety of potential clinical applications.

Objectives  To determine if PDT in bacterially colonized chronic leg ulcers and chronic diabetic foot ulcers can reduce bacterial load, and potentially lead to accelerated wound healing.

Methods  Sixteen patients with chronic leg ulcers and 16 patients with diabetic foot ulcers (each eight active treatment/eight placebo) were recruited into a blinded, randomized, placebo-controlled, single-treatment, Phase IIa trial. All patients had ulcer duration > 3 months, bacterially colonized with > 104 colony-forming units cm−2. After quantitatively assessing pretreatment bacterial load via swabbing, PPA904 or placebo was applied topically to wounds for 15 min, followed immediately by 50 J cm−2 of red light and the wound again sampled for quantitative microbiology. The wound area was measured for up to 3 months following treatment.

Results  Treatment was well tolerated with no reports of pain or other safety issues. In contrast to placebo, patients on active treatment showed a reduction in bacterial load immediately post-treatment (< 0·001). After 3 months, 50% (four of eight) of patients with actively treated chronic leg ulcer showed complete healing, compared with 12% (one of eight) of patients on placebo.

Conclusions  This first controlled study of PDT in chronic wounds demonstrated significant reduction in bacterial load. An apparent trend towards wound healing was observed; further study of this aspect with larger patient numbers is indicated.