Antimicrobial Effectiveness in Eye Drops: Limited Sterility versus Reduction in Microbial Count

Area of Science:

• Pharmaceutical Microbiology
• Ophthalmic Preparations

Background:

• Eye drops require antimicrobial effectiveness testing (AET) as per pharmacopoeias.
• Current AET may not fully reflect real-world contamination risks for ophthalmic products.
• Microbiological specifications for eye drops differ from oral dosage forms.

Purpose of the Study:

• To evaluate the efficacy of eye drops against microbial contamination under simulated real-life usage conditions.
• To compare standard AET results with a novel multichallenge test for ophthalmic preparations.

Main Methods:

• Performed antimicrobial effectiveness testing (AET) on 12 brands of eye drops.
• Compared results against United States Pharmacopeia (USP) <51> and European Pharmacopoeia (Ph Eur) <5.1.3> criteria.
• Designed and implemented a multichallenge test simulating repeated microbial inoculation.

Main Results:

• All tested eye drops met USP <51> and Ph Eur <5.1.3> 'B' criteria.
• Two products failed to meet the 'no recovery' term of Ph Eur <5.1.3> 'A' criteria.
• Products demonstrated self-sterilization within 2 hours when challenged with *Pseudomonas aeruginosa*.

Conclusions:

• All investigated eye drops passed standard AET and the developed multichallenge test.
• The challenge organism population size in standard AET may be excessive for eye drops.
• Pharmacopoeial 'no recovery' terms require clearer definition for ophthalmic preparations.