For drugs with first order kinetics the time required to achieve steady state levels can be predicted from
Volume of distribution
Half life
Clearance
Loading dose
Ans. is 'b' i.e., Half-life Steady stateplasma concentration After 5 t1/2, nearly complete drug is eliminated from the body o If a constant dose of drug is repeated before 5 V/2, 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 t1/2. o With passage of each V/2 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 t1/2 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 t1/2 4 hours and plasma concentration 100 mg/ml 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 t1/2) the drug concentration --> 50 mg/ml. o After 8 hrs (2 t1/2) 75 mg/ml (50 of 1 st dose + 25 of 2" dose) o After 12 hrs (3 t'/2) --> 87.5 mg/ml (50 of 3" dose + 25 of 2" dose + 12.5 of 1' dose) o After 16 hrs (4 t1/2) --> 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 t1/2) --> 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 t1/2) --> 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 t1/2 nearly complete drug elimination occurs & first dose is eliminated after 5 VA). o So, after 5 t1/2 plasma concentration will be constant.