We would like to comment on the ivermectin dose (390 to 470 μg per kilogram of body weight per day) used by Bramante et al. (Aug. 18 issue)
1 in their trial. The 50% inhibitory concentration (IC
50) of ivermectin has been found to be approximately 2.5 μmol per liter, which corresponds to plasma concentrations that are 50 to 100 times as high as the highest concentration in plasma after a single dose of 200 μg per kilogram. Thus, the effective therapeutic dose of ivermectin may be 10 times as high as that permitted.
2 An in vitro study of niclosamide plus ivermectin showed greater efficacy against SARS-CoV-2: the use of the drugs in combination decreased the IC
50 values by up to a factor of 4 relative to the values for each drug alone. This combination may be worth considering for investigation.
3