7 Applications in Pharmaceutical Formulation orTechnologyBenzalkonium chloride is a quaternary ammonium compound usedin pharmaceutical formulations as an antimicrobial preservative inapplications similar to other cationic surfactants, such as cetrimide.In ophthalmic preparations, benzalkonium chloride is one of themost widely used preservatives,(1) at a concentration of0.01–0.02% w/v. Often it is used in combination with otherpreservatives or excipients, particularly 0.1% w/v disodium edetate,to enhance its antimicrobial activity against strains of Pseudomonas.In nasal,(2) and otic formulations a concentration of0.002–0.02% w/v is used, sometimes in combination with0.002–0.005% w/v thimerosal. Benzalkonium chloride 0.01%w/v is also employed as a preservative in small-volume parenteralproducts. Benzalkonium chloride was also shown to enhance thetopical penetration of lorazepam.(3