Which pharmacokinetic parameter is most directly used to determine the maintenance dosing rate of a drug given by continuous intravenous infusion?

Which pharmacokinetic parameter is most directly used to determine the maintenance dosing rate of a drug given by continuous intravenous infusion?
A. Bioavailability
B. Half-life
C. Clearance
D. Volume of distribution

A weakly basic drug has a pKa of 8.0. At a physiological pH of 7.0, which statement best describes its ionisation state?
A. It is completely unionised
B. It is predominantly unionised
C. It exists equally in both forms
D. It is predominantly ionised