Experimental evaluation of cyadox phototoxicity to Balb/c mouse skin

Background: Cyadox is a veterinary drug mainly used as an effective antimicrobial promoter in animal husbandry. It was reported that the other quinoxaline‐1,4‐dioxide compounds had phototoxicity, but only few data are reported on phototoxicity of cyadox. This study was performed to evaluate the phototoxicity of cyadox on skin. Methods: Eighty mice were equally divided into eight groups. Five groups with ultraviolet A (UVA) irradiation for 2 h (21 J/cm2) were administered at doses of 0, 10, 50, 200 mg/kg cyadox and 50 mg/kg olaquindox, respectively, and others as controls without irradiation administered at doses of 0, 200 mg/kg cyadox and 50 mg/kg olaquindox, respectively. Drugs were administered by gavage once daily with a suspension in 0.8% carboxymethyl‐cellulose for consecutive 4 days. After administration, a recovery period of 7 days was arranged. Histopathological examination of auricular skin was performed on days 5 and 12. Measurement of auricular thickness, gross pathology and erythema score were conducted once daily. Results: Cyadox groups (200, 50 and 10 mg/kg) with irradiation had erythema and oedema of auricular skin with dose–response relationship, which gradually convalesced after dosing and irradiation ceased. Severe erythema, oedema and necrosis of auricles were observed on olaquindox group with irradiation. Conclusion: The phototoxicity of cyadox was mild and reversible, which demonstrated a good safety profile of cyadox in terms of phototoxicity.