<prompt> True about t 12 -Time required to reduce the plasma cone, 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 cone, to half Half life T 12 o 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.t 12 0.693 x Vd---CLo After:1 t 12 - 50 drug is eliminated2 t 12 - 75 50 25 drug is eliminated3 t 12 - 87.5 50 25 12.5 drug is eliminated4 t 12 - 93.75 50 25 12.5 6.25 drug is eliminated5 t 12 - 96.875 50 25 12.5 6.25 3.125 drug is eliminatedo Thus, nearly complete drug elimination occurs in 5 half lifes.o For drugs eliminated by :1. First order kinetics - t 12 remains constant2. Zero order kinetics - t 12 increases 