The use of 5-aminolaevulinic acid as a photosensitiser in photodynamic therapy and photodiagnosis

Photodynamic therapy (PDT) is a treatment for cancer and pre-malignant conditions, which involves the administration of a photosensitising agent followed by exposure of the tissue to light. 5-Aminolaevulinic acid (ALA) is a naturally occurring compound in the haem biosynthetic pathway, which is metabolised to a photosensitive product, protoporphyrin IX (PpIX). The major advantage of ALA when compared to synthetic photosensitisers is the rapid metabolism, which significantly reduces the period of cutaneous photosensitivity. This review focuses on the development of ALA as a photosensitiser in photodynamic therapy and photodiagnosis, and the wide range of clinical applications in which ALA is now being used as a therapeutic modality.