<prompt> True about t 12 ?Time required to reduce the plasma conc. to halfZero order kinetics - t 12 remains constantFirst order kinetics - t 12 increasesComplete drug elimination occurs in 2-3 t 12  <response>: Ans. is a i.e., Time required to reduce the plasma conc. to half Half life PA It is the time required to reduce the plasma concentration to half 50 of the original value. It determines the dosing interval and time required to reach the steady state. It is a secondary pharmakokinetic parameter derived from two primary parameters, volume of distribution Vd and clearance CL. 