Cytotoxicity was evaluated in two cell lines, LLCMK2 (in which the antiviral activity of the extracts were assayed) and HepG2, a commonly used liver cell surrogate for in vitro cytotoxicity testing. Cells seeded in 96-well plates were exposed to a wide concentration range of Cipa extract (1–200 μg/ml) for 3 days. Cell viability was assessed using a commercial MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay kit (Sigma, cat. # M5655) with reference to control cells that were not exposed to the extract. The half-maximal cytotoxic concentration (CC50 value) for the herbal extract, with reference to the positive control (untreated cells) which represented 100% cell viability (or 0% cytotoxicity), was defined as the concentration of herbal extract, in μg/ml, resulting in 50% cytotoxicity. Selectivity index (SI) of an extract is defined as the ratio of CC50 to IC50 values obtained using the LLCMK2 cell line.