The slope is poorly written and should be written unambiguously as 0.5/(mg -kg- day). The factors whose units appear in the denominator are multiplicative. Nested slashes are stupid, notch that as another miss by the FDA, middle School kids are taught how to write units and factors correctly. If the unit in the denominator is changed to a smaller unit the number in the numerator has to also become smaller in order to keep the value of the constant, well, *constant.*