Aminolevulinic Acid: Bright Future for a New Photodynamic Therapy for Actinic Keratosis?

New Therapy: Bright Future?

A new photodynamic therapy for the treatment of actinic ketoses on the face and scalp has recently been approved. This novel approach first involves the topical application of aminolevulinic acid, a natural precursor of heme, which is preferentially taken up by actinic keratoses cells and converted to protoporphyrin IX, a potent photosensitiser. When protoporphyrin IX is exposed to light with wavelengths that range from 405nm (blue) to 635nm (red), cytotoxic reactive oxygen species and free radicals are generated which effectively destroy the tumour.^[4]

Aminolevulinic acid does not cause photosensitisation of normal skin,^[5] although sun-damaged but otherwise healthy skin does become photosensitised after topical application of this agent.^[6] Because actinic keratoses are often surrounded by sun-damaged skin, care should be taken when applying it to minimise adverse effects on perilesional areas.

A feature of the development of aminolevulinic acid photodynamic therapy has been the diversity of the regimens used as researchers endeavoured to optimise treatment.^[4] A standardised protocol has now been developed and approved for clinical use of actinic lesions on the face and scalp.

To ensure accurate application of topical aminolevulinic acid, a dermatological applicator is used to apply the solution. The applicator tip is attached to a flexible plastic tube containing 2 glass vials: 1 containing aminolevulinic acid in powder form and the other an ethanol based solvent. When mixed together, these two produce a 20% weight/volume aminolevulinic acid solution (approximately 50% ethanol) which is applied by gently dabbing the lesion. Aminolevulinic acid is not intended to treat the entire face, but rather is to be used to treat up to 15 individual actinic keratoses.^[2]

Fourteen to 18 hours after application of aminolevulinic acid, the patient undergoes blue light irradiation (patients are advised to stay out of the sun in the interim). During this process, the treated lesions are exposed to blue light at a wavelength of 417nm for 1000 seconds (light dose of 10 J/cm²). If the treated lesions have not cleared by 8 weeks the treatment can be repeated.

© 2001 Adis Data Information BV

Cite this: Aminolevulinic Acid: Bright Future for a New Photodynamic Therapy for Actinic Keratosis? - Medscape - Jan 29, 2001.