Continuous(multiple)dose kinetics Q CI(KE)(Va) Where Cs=steady state drug concentration;Q=infusion rate or dose per unit time; CI=total body clearance:K=elimination constant:V=volume of distribution The amount of time it takes to achieve the steady-state concentration is dependent on the elimination constant only.The equation for drug accumulation in plasma is similar to the equation for drug elimination: Cr =Css(1-ekeT) If a patient receives a constant infusion of a drug,the plasma drug concentration will be50% (1-1/2'=1/2)of the steady state concentration in one half-life,and 97%(1-1/2=31/32)of the steady state concentration in 5 half-lives. Continuous(multiple)dose kinetics Infusion started Infusion started Steady state approached 7 in about 5 t12 0 2t2 4t12 0 0 6 78 9 10 Time (t1/2)Continuous (multiple) dose kinetics Continuous (multiple) dose kinetics