Microbiological and physicochemical assessment of some brands of gentamicin eye drops marketed in registered retail pharmacies in Port Harcourt, Nigeria

Gentamicin eye drop is the most commonly imported, often abused, cheap anti-infective for most superficial eye infections in Nigeria. This study therefore aims at determining the physicochemical properties and the antimicrobial efficiency of nine brands of the multi-dose Gentamicin eye drops purchased from registered retail pharmacies in Port Harcourt, Rivers state, Nigeria. Nine brands of gentamicin sulphate eye drops were purchased from different pharmacies in Port Harcourt metropolis. Physical appearance of the different brands were examined for integrity of the packaging and closure system. In addition to physicochemical analysis (colour and clarity evaluation, pH) sterility testing was done by inoculating each differentiating nutrient media (liquid thioglycollate, soya casein, and Sabouraud dextrose media) with different eye drop sample. Microbial challenge test on the effectiveness of the preservative (using E. coli, P. aeruginosa, S. aureus and C. albicans) and pyrogen testing were conducted on the samples. All the samples in vials were packaged properly with no particulate matter in any of them. The pH of the brands ranged from 5.40 - 7.26. All the nine samples of gentamicin eye drops passed the “on the spot” sterility testing. One of the 9 samples (11.11%) failed the preservative challenge test while 4 samples (44.44%) failed the pyrogen test for bacterial endotoxin. An eye product may be sterile but not pyrogen-free. The efficiency of the preservative system in a sterile gentamicin eye drop solution is to confer the eye drop with the ability to withstand contamination by opportunistic microorganisms during usage.