<prompt> Young child weighing 20 kg was given a drug in the dose 100mgkg body weight. The plasma concentration of the drug is 2mg dl and the clearance is 200 mlhr. What is the time required to reach steady state plasma concentration -10 hrs20hrs30hrs40hrs  <response>: Ans. is b i.e., 20 hours Volume of distribution total doseplasma concentration Total dose dose kg x body weight 100 x 20 2000 mg Volume of distribution 20002 1000 Half life 0.693 x Volume of distribution clearance 0.693 x 1000200 3.5 hours Time required to reach steady state plasma concentration is 5.5 half lives 5.5 x 3.5 19.25 hours Therefore the most appropriate answer is 20 hours. 