Review of inactive ingredients in antibiotic ear drops.

The authors review the relevant chemical and biological characteristics of inactive ingredients in antibiotic ear drop drug products. Although many of the older aminoglycoside-containing otic products are still used today, only some fluoroquinolone-containing ear drops, approved in the last decade, have been proven safe and effective according to current rigorous scientific standards, including ototoxicity testing of the formulations. Preservatives, antioxidants, surfactants, buffers, suspending and emulsifying agents, osmotic agents, viscosity modifiers, solvents, and penetration enhancers are reviewed with regard to their functional role in formulations, as well as their potential for ototoxicity.