Chinelo K Ezejiegu1,
Benjamin O Anyigor1,
Emmanuel C Ezejiegu2,
Frances E Okonkwo1,
Ijeoma N Ebenebe1 
,
Goodness UM Nwaneri1
For correspondence:- Ijeoma Ebenebe Email: in.ebenebe@unizik.edu.ng Tel:+234 802 7759 423
Received: 24 March 2026 Accepted: 16 September 2026 Published: 30 September 2026
Citation: Ezejiegu CK, Anyigor BO, Ezejiegu EC, Okonkwo FE, Ebenebe IN, Nwaneri GU. Assessment of preservative effectiveness in preserved and preservative-free artificial tears eye drops by microbial challenge test. Trop J Pharm Res 2026; 25(9):1209-1215 doi: 10.4314/tjpr.v25i9.3
© 2026 The authors.
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Purpose: To assess and compare the preservative effectiveness of preserved and preservative-free artificial tears. Methods: Eight artificial tear products were randomly purchased from registered pharmacies. The products were classified as preserved (n = 4) or preservative-free (n = 4) based on the presence (containing benzalkonium chloride) or absence of a preservative. Physicochemical evaluation, including colour, clarity, particulate matter, and pH, was carried out for all products. In addition, baseline microbiological quality assessment of each product was carried out using a culture-based viable cell count method, targeted at determining the sterility of the test products before the challenge test and after exposure to ambient air to simulate typical usage. Microbial challenge tests were performed using Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Aspergillus niger. Results were periodically (0, 7, 14, and 28 days) monitored and surviving organisms were determined by serial dilution and pour-plate viable cell count. Results: The study recorded 100 % clear, colourless, and particle-free products, with pH values ranging from 6 to 9. Preserved formulations generally resisted microbial contamination better than preservative-free products. Air exposure led to microbial growth in all products except P-4, which remained stable throughout the 28 days. Preserved drops significantly reduced bacterial and fungal contamination at the end of the microbial challenge test, while preservative-free drops exhibited higher microbial survival over time. Conclusion: Although the preserved eyedrops offered better protection against contamination, when compared to the unpreserved eyedrops, only one out of 4 tested had a total absence of microbial contamination throughout the 28 days of testing. These results buttress the protective role of preservatives in ophthalmic preparations and the need for careful handling of these products
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