<prompt> A steady state plasma concentration is achieved in how many hours, if half life of drug is 40 hrs. ?140hrs160hrs180hrs200 hrs  <response>: Ans. is c i.e., 200 hrs 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. Thus for a drug with T12 40 hrs to reach the steady state plasma concentration 5 t12s will be required. i. e. 5 X 40 hrs 200 hrs. 