The only photosensitizer currently used in the clinic other
than the haematoporphyrin derivatives is methylene blue, which is used by the Swiss and German Red
Cross for the decontamination of freshly frozen plasma
units. This photosensitizer effectively inactivates extracellularly
enveloped viruses and is used in the clinic as a
treatment for methaemoglobinaemia, thus showing its lack
of toxicity in humans.
This phenothiazinium dye has
been used extensively for over a century as a biological
assay stain and can be used in the clinical diagnosis of a
variety of diseases and as a tumour marker in surgery.
However, its use as an in vivo photosensitizer is limited by
its reduction by ubiquitous cellular enzymes to the colourless
form, which is photodynamically inactive.