Unlike animal-based toxicology testing, there are clearer definitions and greater agreement for what constitutes cytotoxicity in vitro. Classically speaking, a compound or treatment is considered to be cytotoxic if it prevents cellular attachment, causes dramatic morphological changes, adversely affects replication rate, or leads to a reduction in overall viability [2] . It should be noted that the manifestation of these effects is greatly dependent on length of compound exposure and mechanism of cytotoxicity [3] .