In Vitro Bactericidal Activity of Propamidine 0.1% and Other Ophthalmic Antiseptics on Conjunctivitis and Blepharitis Strains

The aim of this study was to assess the in vitro antimicrobial activity of propamidine isethionate 0.1% ophthalmic solution and other topical antiseptics, including hexamidine di-isethionate 0.1%, cethexonium bromide 0.025%, and picloxydine hydrochloride 0.05%.

Antibacterial activity was tested in vitro on five Gram-positive bacterial strains commonly found in conjunctivitis and/or blepharitis. Test products were applied at a concentration of 80% at 20 °C (in accordance with NF EN 1040) for contact periods of 2, 5, 10, and 15 min. After neutralization, surviving bacteria were cultured, and colony forming units (CFU) were counted. Antimicrobial efficacy was expressed as log reduction in CFU. Bactericidal activity was defined as a reduction > 5 log.

All tested antiseptics demonstrated antibacterial activity with variability in magnitude of their effects depending on the bacterial strain and contact time. Propamidine 0.1% showed rapid activity, achieving maximal log reduction within 2 min against Staphylococcus epidermidis, Streptococcus pneumoniae, and Propionibacterium acnes. Cethexonium bromide 0.025% exhibited the highest antibacterial activity, with bactericidal effects observed against Corynebacterium striatum, S. pneumoniae, and P. acnes; hexamidine 0.1% and picloxydine 0.05% showed more limited or inconsistent bactericidal activity.

All tested antiseptics demonstrated measurable in vitro antibacterial activity against common pathogens associated with conjunctivitis and blepharitis. The observed variability in antimicrobial magnitude highlight the influence of bacterial strain and exposure conditions on antiseptic performance. These results support the potential clinical interest of ocular antiseptics, including propamidine 0.1% in the management of mild bacterial conjunctivitis and blepharitis, although confirmation under clinical conditions remains necessary.