The effects of topical nasal steroids on rat respiratory mucosa in vivo, with special reference to benzalkonium chloride.

Fifty rats were treated with topical nasal steroids with and without the preservative benzalkonium chloride in their right nostril twice daily for 21 days, while the left nostrils were exposed to 0.9% NaCl. By cutting the noses serially in frontal sections, the structure of the mucosal lining of all parts of the nose could be investigated. Areas with squamous cell metaplasia were observed in all nostrils exposed to topical steroids containing benzalkonium chloride. Such alterations were not observed in any nasal cavities exposed to the topical nasal steroid without the preservative or to 0.9% NaCl. In conclusion, benzalkonium chloride appears to be potentially toxic to the mucosa in vivo.