Antimicrobial effectiveness must be demonstrated for aqueous-based, multiple-dose topical and oral dosage forms and for other dosage forms such as ophthalmic, otic, nasal, irrigation, and dialysis fluids. The ability of the procedure to detect challenge microorganisms in the presence of a suitably neutralized product to be tested must be established. The suitability of the procedure must be reconfirmed if a change is made in materials or methods or if a change is made in the product or direct product contact materials that may affect the outcome of the test. As per reference USP chapter <1226> verification of compendial procedures, Users of compendial analytical procedures are not required to validate these procedures when first used in their laboratories, but documented evidence of suitability should be established under actual conditions of use. In the United States, this requirement is established in 21 CFR 211.194(a)(2) of the current Good Manufacturing Practice regulations, which states that the “suitability of all testing methods used shall be verified under actual conditions of use.” The verification process for compendial test procedures is the assessment of whether the procedure can be used for its intended purpose, under the actual conditions of use for a specified drug substance and/or drug product matrix. As per reference USP chapter <1227> validation of microbial recovery from pharmacopoeial articles, the test procedures in Antimicrobial Effectiveness Testing <51>, are considered validated. However, use of compendial methods requires establishment of suitability of the method demonstrating recovery of the challenge organisms in the presence of the product. Alternatives/modifications to these recovery procedures beyond what are described in these chapters (such as dilution, chemical or enzymatic neutralization, and membrane filtration) require validation. It is generally understood that if a product possesses antimicrobial properties because of the presence of a specific preservative or because of its formulation, this antimicrobial property must be neutralized to recover viable microorganisms. This neutralization may be achieved by the use of a specific neutralizer, by dilution, by a combination of dilution, filtration, and rinsing, or by any combination of these methods.