Comparative photodynamic evaluation of new phenothiazinium derivatives against Propionibacterium acnes

The screening of recently patented derivatives of the standard phenothiazinium agents methylene blue and toluidine blue was carried out against Propionibacterium acnes, the main bacterium associated with acne vulgaris. Comparative tests were made using the topical agent benzoyl peroxide (BPO) and standard tetracyclines. Each of the photosensitizers employed, including the lead compounds, was photobactericidal at lower concentrations than BPO, and produced a much more rapid kill than the tetracyclines. In addition, the tetracyclic and pentacyclic phenothiazinium derivatives exhibited high light:dark kill ratios, suggesting that these examples might be particularly useful in practice.