hi
can anybody tell me what are the different parameters for testing physical properties of a sample in stability study of a drug product.

From Q1A(R2) Stability Testing of New Drug Substances and Products (http://www.fda.gov/cber/gdlns/ichstab.pdf) (PDF document):

Stability studies should include testing of those attributes of the drug substance that are susceptible to change during storage and are likely to influence quality, safety, and/or efficacy.

We do aqueous topical antimicrobials, so we check active ingredient assay, appearance, pH and viscosity.

Edit: I moved this to the FDA forum.