Glossary of Terms

Phototoxicity

Phototoxicity is the most common mechanism of drug-induced photosensitivity. It occurs in any individual exposed to sufficient phototoxic chemical and light of the appropriate wavelength. Psoralens, porphyrins and tar are examples of phototoxic agents. There is a wide range of possible clinical presentations, including exaggerated sunburn, prickling, oedema and urticaria, due to accumulation of drug or metabolite at different subcellular sites.

Photogenotoxicity

Photogenotoxicity is a genotoxic response observed after exposure to a chemical photoactivated by UV or visible light. A genotoxic response is one that is capable of damaging the genetic material. The main purpose of photogenotoxicity testing is to make an assessment of the potential of a compound to turn into a photochemical carcinogen upon activation with UV or visible radiation.

Photoactivated therapeutics

Photoactivated therapeutics refers to the use of pro-drugs which are activated by light. Potentially, this can reduced unwanted side-effects because the drug is only activated by exposure to light at the tumour site and is not toxic in the dark.

Photosafety

Photosafety testing is designed to detect the adverse effects of a drug in the presence of light. This type of testing is relevant for a substance that enters the skin via dermal penetration or systemic circulation. Photobiological reactions normally occur when a chemical is able to absorb UV or visible light.

Drug Development

Drug development is the process of taking a new chemical lead through the stages necessary to allow it to be tested in human clinical trials and thereafter to assess safety, toxicity, pharmacokinetics and metabolism in humans.