Abstract: Stable, clear, antimicrobially effective, ophthalmic formulations include an ophthalmologically effective amount of a drug, especially a --COOH group-containing drug or a NSAID, and a preservative system formed of a quaternary ammonium preservative and a nonionic surfactant, all in an aqueous vehicle. These formulations are useful for treating diseases that are either caused by, associated with or accompanied by inflammatory processes, including, among others, glaucoma, cystoid macular edema, uveitis, diabetic retinopathy and conjunctivitis, or any trauma caused by eye surgery or eye injury.