PDT effective for acne

PDT MECHANISMS Photodynamic therapy (PDT) offers two mechanisms for treating acne by producing free radical damage that leads to cell death.

The first, endogenous photodynamic therapy, activates protoporphyrin IX - a strong photo-sensitizer within the P. acnes bacteria - to produce free radicals and, subsequently, bacterial death in the sebaceous gland.

Various wavelengths can be used, including blue light, green light, pulsed dye laser and intense pulsed light sources. Blue light therapy is one of the most widely studied, and Dr. Kauvar describes a multicenter trial using eight biweekly treatments, showing generally a 60 percent to 70 percent reduction of acne after a series of eight treatments (J Drugs Dermatol 2005 Jan-Feb;4(1):64-70).

One drawback for blue light therapy or other lasers or light sources that work the same way is that results are not long-lasting.

"You can get short-term improvement but this is not a long-term therapy," Dr. Kauvar explains.

The treatment, nevertheless, can be a very useful adjunct therapy, used with other topical or oral medications, and it can be an excellent modality during pregnancy, when use of other therapies is limited, Dr Kauvar adds.

EXOGENOUS PDT Exogenous PDT enjoys greater use in the United States.

The treatment uses aminolevulinic acid (ALA) that is applied to the skin topically or systemically.

Levulan (Dusa Pharmaceuticals), a 20 percent solution of topical 5-ALA, is the most popular ALA product used in the United States for acne. The molecule penetrates the skin and preferentially accumulates in rapidly dividing cells in sebaceous glands and, to a lesser degree, in hair follicles. It then is metabolized by the cells to protoporphyrin IX, which can be activated by a wide variety of light sources, also to produce free radicals and cell death in any cell that has absorbed the ALA.

ALA STUDIES Dr. Kauvar refers to several studies showing acne improvement from the ALA-PDT therapy, including one which showed a significant reduction in acne lesion counts up to 20 weeks after one to four treatments.

But, with high exposures to both the drugs and the light (a red light source at 150 joules per cm² ), and they found the patients had acute toxicity reactions, including erythema, edema and folliculitis, which lasted as long as two weeks (J Invest Dermatol. 2000 Aug;115(2):183-192).

With the majority of acne sufferers being adolescent and young adult patients, side effects of redness and peeling can be a big deterrent, so researchers looked for alternatives.

"The goal was to try to reduce the adverse effects, and it was done by means of using light sources that were less efficiently absorbed by the drug, causing less of a response," Dr. Kauvar says.

Intense pulsed light (IPL), pulsed dye laser and lower doses of blue light, in addition to a lower incubation with the drug, were just a few changes that were shown to help reduce morbidity.

Dr. Kauvar refers to a study of patients with mild-to-severe acne, in which ALA was activated with IPL, using a short incubation time of one hour. Eleven of 15 patients responded, and there was a 50 percent reduction of acne lesions after a four-week treatment, and at the 12-week follow up there was a 72 percent decrease in lesions (J Drugs Dermatol. 2004 Nov-Dec;3(6 Suppl):S10-14).