True about t 1/2 -

Ans. is 'a' i.e., Time required to reduce the plasma cone, to half Half life T 1/2 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 1/2 =0.693 x Vd----------CLo After:1 t 1/2 - 50% drug is eliminated2 t 1/2 - 75% (50 + 25) drug is eliminated3 t 1/2 - 87.5% (50 + 25+ 12.5) drug is eliminated4 t 1/2 - 93.75% (50 + 25 + 12.5 + 6.25) drug is eliminated5 t 1/2 - 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 1/2 remains constant2. Zero order kinetics - t 1/2 increases