Topical ocular delivery of fluoroquinolones

Introduction: Topical fluoroquinolones are used in ophthalmology to treat ocular infections. They are bactericidal and inhibit bacterial DNA replication by inhibiting DNA gyrase and topoisomerase. Fluoroquinolones possess two ionizable groups: a carboxylic group (pKa(1) = 5.5 - 6.34) and a heterocyclic group (pKa(2) = 7.6 - 9.3), in the nucleus, which acquire charge at pH above and below the isoelectric point (pI = 6.75 - 7.78). At isoelectric point, fluoroquinolones remain unionized and show enhanced corneal penetration but exhibit reduced aqueous solubility and the drug may precipitate from aqueous solution. Aqueous ophthalmic solutions of fluoroquinolones are obtained by using hydrochloride or mesylate salt which is acidic and irritating to the eyes. Hence, pH of the solution is kept between 5 and 7 to ensure aqueous solubility and minimum ocular irritation. Areas covered: This review gives an overview of various physicochemical and formulation factors affecting the ocular delivery of fluoroquinolones and strategies for getting higher ocular bioavailability for ocular delivery of fluoroquinolones. These strategies could be employed to improve efficacy of fluoroquinolones in eye preparation. Expert opinion: Broad-spectrum antibacterials, such as the ophthalmic fluoroquinolones, are powerful weapons for treating and preventing potentially sight-threatening infections. The fourth-generation fluoroquinolones have quickly assumed an outstanding place in the ophthalmic applications. Especially valuable for their broad-spectrum coverage against Gram-positive and Gram-negative organisms, these agents have become the anti-infective of preference for many ophthalmologists. Moxifloxacin seems to be a promising powerful molecule among all fluoroquinolones for treatment of bacterial infections.