Importantly, despite the fact that amantadine had no significant antiviral activity as a single agent below 3.2 mg/mL (data not shown), we find that the amantadine contributed to the activity of the TCAD regimen at clinically achievable concentrations (0.43 mg/mL). Statistical analysis of the variability across all replicates from the six experiments for each virus revealed that amantadine made a significant contribution to the synergy of the TCAD regimen at concentrations 0.1 mg/mL and 0.32 mg/mL and above against CA05 and CA10, respectively, compared to the double combination of ribavirin/oseltamivir carboxylate without amantadine ( Figure 1B ). For CA04, while only the 3.2 mg/mL amantadine concentration had statistically significant greater synergy volume than the double combination without amantadine, there was a trend toward increasing synergy volume starting at 0.32 mg/mL. Thus, amantadine contributed to the activity of the TCAD regimen at concentrations where it was inactive as a single agent, and at concentrations that were clinically achievable.