What is Preservative Efficacy Test of the pharmaceuticals formulations?

What is Preservative Efficacy Test of the pharmaceuticals formulations?

What is PET or AET?

Antimicrobial preservatives are substances that are added to products to protect them from microorganisms that are introduced inadvertently during or subsequent to the manufacturing process. In the case of products packaged in multiple-dose containers, antimicrobial preservatives are added to inhibit the growth of microorganisms.

Preservative efficacy test or Antimicrobial effectiveness test

The Antimicrobial effectiveness test, also known as the preservative efficacy test, is performed to determine if the chosen preservative is appropriate for a product formulation. It is also carried out as part of a stability study, to ascertain whether a preservative system is still effective up to the expiration date of a product.Products such as multi-dose pharmaceutical medicines, cosmetic products, personal care products will normally contain preservatives and needs to be tested.


Antimicrobial preservatives are added to products to prevent or inhibit microbial contamination, which can occur during normal conditions of storage and use. The efficacy of an antimicrobial preservative may be enhanced or reduced by the active constituent of the preparation, or by the formulation in which it is incorporated, or by the container and/or closure being used as the final packaging material.
The test method must be qualified for the product.
The product must be challenged within individual containers, each going through this process separately using one of the five required organisms, which include ATCC established strains of E. coli, S. aureus, P. auruginosa, C. albicans, and A. brasiliensis. The inoculated product is held at room temperature for 28 days.  It is examined by the duplicate plate count method to determine the number of viable microorganisms which survive at each specified time interval. 
The PET assay measures the reduction of a high inoculum (106-107 cfu/g) in the presence of a product containing preservative over 28 days, which also tests the ability of the preservative to prevent a re-growth.
All results are evaluated in accordance with the tabulated acceptance criteria of the relevant Pharmacopoeia’s or test protocols.