Abstract: Objective To find out the optimal 5-aminolevulinic acid (ALA) concentration and duration of topical use in ALA-photodynamic therapy (ALA-PDT) for urethral warts.Methods Sixty patients with urethral warts were recruited into the study.ALA solution was applied to warty lesions in concentrations of 0.5%,1%,3%,5% and 10%,for 1,3,5 and 7 h before biopsy.The fluorescence pattern of ALA induced protoporphyrinⅨ(PPⅨ) was quantified by fluorescence microscopy and digital image analysis in cryosections.The presence of low-or high-risk types of HPV was tested by FDA approved Hybrid Capture 2 HPV DNA assay.Results ALA-induced PPⅨ fluorescence was found in the epidermis in almost all of patients after application of 5-ALA,but hardly found in dermis.The intensity of PPIX fluorescence became strong at 3 h after application,reached peak at 5 h,and gradually declined afterwards.The equal intensity was identified between 3 h and 7 h after application.The intensity of PPⅨfluorescence increased gradually in epidermis along with the increasing of ALA concentrations,which was stronger with 5% and 10% compared to as compared that with 0.5%,1% and 3% ALA solution (P<0.05).Low-risk types were identified in all patients while high-risk types in 18.3% (11/60) simultaneously.Conclusions The results strongly suggest that ALA-PDT with 5% and 10% ALA applied for 3-5 hours is optimal for the treatment of urethral warts.

Key words: Condylomata acuminata, Aminolevulinic acid, Protoporphyrins, Photochemotherapy