Each drug has a definite shelf life when the stocks are prepared and stored aliquoted following the manufacturer's protocol. Freezing and reusing any drug after thawing and is not recommended. Fresh prepared stocks are definitely better but not always possible to have it due to financial constraints.
Actually my drug is a crude plant extract and I store it at 4 degree only, I never freeze it! Does any one have a good literature for making plant based drugs for treating cancer cell lines.