Systemic photobiological effects of xenobiotics

Simultaneous exposure to (sun)light and a xenobiotic may result in systemic effects. Two examples of this research will be dealt with in this paper. The first concerns olaquindox (OX) which, like carbadox and cyadox, is a growth-promoting substance used as an additive to pig feed. OX has two imino-N-oxide groups. The imino-N-oxide group has been proven to be the cause of the phototoxicity of chlordiazepoxide (CDZ). In that case systemic effects included a profound change of urinary metabolism, covalent binding of CDZ fragments to liver and kidney tissue, and a 25%-30% decrease of liver/total weight. The quinoxaline-1,4-dioxides are extremely photolabile. Quindoxin caused several cases of photocontact dermatitis and has been removed from the market. OX has been reported to be phototoxic in pigs.