Optimization of topical photodynamic therapy with 3,7-bis(di-n-butylamino)phenothiazin-5-ium bromide for cutaneous leishmaniasis

Background and objective: Photodynamic therapy (PDT) has evolved as a promising therapeutic measure for the treatment of cutaneous leishmaniasis (CL). In particular, phenothiazine compounds have demonstrated efficacy for PDT of CL. The objective of our present study is to define the use of a new specific phenothiazine photosensitizer, 3,7-bis(di-n-butylamino)phenothiazin-5-ium bromide (PPA904) applied topically as a cream to treat CL.

Materials and methods: To establish the optimal conditions for this treatment, we compared two different ways to improve current regimens of PDT with PPA904 cream (500 microM of PPA904 in Unguentum M) by changing the duration of topical application, and by administration of several consecutive PDT procedures. An initial regimen recommended by the manufacturer (Photopharmica Co. Ltd., Leeds, UK) was maintained as a control: the cream was applied topically for 30 minutes at a final concentration of PPA904 at 500 microM, and the designated treatment area was irradiated with a broad band LIGHT source of 665+/-15 nm at a fluence of 50 J/cm(2) (50 mW/cm(2)).

Results: The best curative PPA904-PDT regimen was achieved under the conditions of a longer duration of topical application time (90 minutes) and several (three) consecutive treatments with 4-day intervals between treatments. The mechanisms responsible for such improvements (kinetics of drug penetration, depth of necrosis of the CL lesions after PDT, and daily changes in the parasitic load after PDT) are discussed in the present study.

Conclusion: Topical PPA904-PDT, implemented as described above, is a promising treatment for CL, and clinical studies will be initiated to establish efficacy in humans.