<prompt> For drugs with first order kinetics the time required to achieve steady state levels can be predicted fromVolume of distributionHalf lifeClearanceLoading dose  <response>: Ans. is b i.e., Half-life Steady stateplasma concentration After 5 t12, nearly complete drug is eliminated from the body o If a constant dose of drug is repeated before 5 V2, the concentration in blood will be higher, because some remnant of the previous dose will be present in the body. o So, when a drug is infused at a constant rate the plasma concentration rises until a state is reached at which the rate of administration of drug to the body is exactly equal to the rate of elimination. o This is called the steady state --- when it is attained the amount of drug in the body remains constant i.e. the plasma concentration is on a plateau --- plateau principal of drug accumulation. o If a drug is administered by a constant rate the time to reach steady state depends only on the t12. o With passage of each V2 period of time, the plasma concentration rises by half the difference between the current concentration and the ultimate steady state 100 concentration. o For all practical purposes, after 5 t12 the amount of drug in the body will be constant and the plasma concentration will be at a plateau. o For example, if a drug with t12 4 hours and plasma concentration 100 mgml is given at a constant rate ie every 4 hrs. 1st dose -- at 0 hrs 2nd dose -- at 4 hrs 3rd dose at 8 hrs 4th dose -- at 12 hrs--- so on. o After 4 hrs 1 t12 the drug concentration -- 50 mgml. o After 8 hrs 2 t12 75 mgml 50 of 1 st dose 25 of 2 dose o After 12 hrs 3 t2 -- 87.5 mgml 50 of 3 dose 25 of 2 dose 12.5 of 1 dose o After 16 hrs 4 t12 -- 93.75 50 of 4th dose 25 of 3rd dose 12.5 of 2 dose 6.25 of 1 dose o After 20 hrs 5 t12 -- 96.875 50 of 5th dose 25 of 4th dose 12.5 of 3rd dose 6.25 of 2 dose 3.125 of V dose o After 24 hrs 6 t12 -- 96.875 50 of 6th dose 25 of 5th dose 12.5 of 4th dose 6.25 fo 3rd dose 3.125 of 2 dose nil from 1st dose, after 5 t12 nearly complete drug elimination occurs first dose is eliminated after 5 VA. o So, after 5 t12 plasma concentration will be constant. 