<prompt> If a patient was given 1000 mg of a drug 1st order kinetics initially and after 2 hours the drug level in plasma is 500 mg, after 8 hours what will be the level in plasma?125 mg62.5 mg0 mg31 mg  <response>: B 62.5 If we measure the slope of this curve at a number of times we are actually measuring the rate of change of concentration at each time point, ACpA, represented by the straight line tangents in Figure. First order kinetics: Constant Fraction of drug is eliminated at constant interval of time i.e.., 50 of drug is eliminated at every t12. Rate of elimination is directly proportional to drug administered. In this case the drug is following first order kinetics, drug administered is 1000 mg, t12 is 120 min. So, 1000 mg - 500 mg in 2hrs - 250 mg in 2hrs -125 mg in 2hrs. Totally after 8 hours the drug remained is 62.5 mg 