Uses of Photodynamic Therapy in Dermatology
The only FDA-approved indication for ALA photodynamic therapy (PDT) and MAL photodynamic therapy in dermatology is currently the treatment of AKs. Common off-label uses include the treatment of BCC, photoaging, acne vulgaris, and Bowen disease. Less common off-label indications are possible. Also see the clinical guideline summary from the British Association of Dermatologists,
Both ALA and MAL are approved in several countries, including the United States (by the FDA), for the treatment of AK. In the FDA-approved protocol, ALA is to be applied on AKs only, followed 14-18 hours later by 10 J/cm2 of blue light exposure using the Blu-U device. In phase 3 studies, lesions of 243 patients were treated once with ALA photodynamic therapy and were re-treated at 8 weeks if they did not show a complete response. The complete clinical response of individual lesions at week 12 was 91%, with just one ALA photodynamic therapy session. The percentage of patients who had a complete response with all lesions was 73% at week 12. However, in clinical practice, most physicians are currently using shorter (30-90 min) incubation times for the treatment of AK. This short incubation period has not yet been approved by regulatory authorities.
Although the FDA-approved protocol involves the application of ALA only on individual lesions, many physicians are now using broad applications on facial areas where multiple ill-defined AKs or concomitant photoaging is present. This has the theoretical advantage of treating subclinical precancerous lesions. In studies using the hairless mouse as a model, multiple broad-area ALA and MAL applications followed by light exposure have been shown to delay the appearance of AK and SCC. If broad-area application is used, clinicians should be careful when using intervals of longer than 1 hour between drug application and light exposure. The phototoxic reaction (redness, burning sensation, scabbing, crusting) observed after ALA and MAL is significantly stronger with longer exposure time.
Physicians are also currently using light sources other than the FDA-approved Blu-U for the treatment of AK. These include intense pulsed light and pulse dye laser. Limited data are available on the efficacy of these light sources combined with ALA for the treatment of AK.