Young child weighing 20 kg was given a drug in the dose lOOmg/kg body weight. The plasma concentration of the drug is 2mg/ dl and the clearance is 200 ml/hr. What is the time required to reach steady state plasma concentration -

Ans. is 'b' i.e., 20 hourso Volume of distribution = total dose/plasma concentrationo Total dose= dose/ kg x body weight = 100 x 20 = 2000 mgo Volume of distribution = 2000/2 = 1000o Half life = 0[?]693 x Volume of distribution/ clearance = 0[?]693 x 1000/200 = 3[?]5 hourso Time required to reach steady state plasma concentration is 5-5 half lives = 5[?]5 x 3[?]5 = 19[?]25 hourso Therefore the most appropriate answer is 20 hours.