This topic came up shortly after the PR and I'm not sure anyone has a correct answer. First you can make some pretty large initial assumptions: 1) all substances involved have a specific gravity of 1.0; and 2) you completely ignore the differences between laboratory testing in a sample container (e.g. petri dish) and clinical testing in a human body.

The ABSSSI trial used 0.8 mg/kg for one of the IV dosings. For an IV, that typically is the amount of drug with respect to the amount of fluid in the delivery. So, 0.8mg of Brilacidin in a kilogram of crystalloid fluid (e.g. saline 0.9%).

the conversion to µg/ml as was used in the laboratory, given the assumptions above, would actually work out straight across to mg/kg, so 0.8µg/ml.

Now how you would calculate the actual concentration in a persons bloodstream with respect to the concentration in the laboratory test - have fun