Influence of topical photodynamic therapy with 5-aminolevulinic acid on porphyrin metabolism.

Photodynamic therapy (PDT) with topically applied 5-aminolaevulinic acid (5-ALA) is increasingly used for treating tumours. The efficacy of topical PDT is limited to superficial and initial tumours. The topically applied doses of 5-ALA vary from 0.02 to 7.0 g per session according to the type of lesion. There are no studies on the influence of topically applied 5-ALA on the systemic accumulation of porphyrins or porphyrin precursors. A group of 20 patients with actinic keratoses (AK) and basal cell carcinomas (BCC) were treated by topical PDT with 5-ALA. Prior to and 6 and 24 h after PDT, 5-ALA and total porphyrin concentrations were determined in red blood cells and plasma, respectively. In addition, before and after 5-ALA treatment, 24-h urine samples were collected and porphyrins and porphyrin precursors were measured. There was no significant alteration in porphyrin metabolism. In some patients, a slight but insignificant increase in erythrocyte and plasma porphyrins was found 6 h after 5-ALA PDT. This investigation confirms clearly the safety of this treatment modality and demonstrates that 5-ALA application (up to 7 g) in the course of PDT has no influence on the concentrations of porphyrins and porphyrin precursors measured in various compartments.