Synergy volume for each double and triple combination was also calculated, which represents the sum of the synergy or antagonism across all concentrations of a combination. Synergy volumes are presented as a quantitative measure of the overall interaction of the drugs within a combination. As determined by cytopathic effect (Neutral Red assay), synergy volumes .100 mg/ mL 2 % for double combinations or .100 mg/mL 3 % for triple combinations are considered to be strongly synergistic. Conversely, combinations with synergy volumes ,2100 mg/mL 2 % or mg/ mL 3 % are considered to be strongly antagonistic.