Singlet oxygen production and in vitro phototoxicity studies on fenofibrate, mycophenolate mofetil, trifusal, and their active metabolites

Singlet oxygen photosensitization (studied by time-resolved near-infrared emission spectroscopy) and in vitro phototoxicity (by means of the 3T3 neutral red uptake assay) have been investigated for the prodrugs fenofibrate (FFB), mycophenolate mofetil (MMP), and trifusal (TFS) as well as for their active metabolites fenofibric acid (FFA), mycophenolic acid (MPA), and 2-hydroxy-4-(trifluoromethyl)benzoic acid (HTB). The results show that FFB and its active metabolite FFA generate ¹O₂ with a quantum yield in the range 0.30 to 0.40 and show a photo-irritation factor (PIF) higher than 40. By contrast, MMP/MPA and TFS/HTB are not photoactive in the used assays. These results correlate well with the previously reported in vivo phototoxicity in treated patients.