Case Study 1 Fall 2010 1) a) Define Pharmacokinetics? b) Fig 1 shows the plasma concentration time profiles of three subjects A, B and C after the administration of the same dose of a drug X. i) From the profile explain the differences in the route of administration between the subjects. Write a short answer in terms of LADME. ii) Between subjects A and B identify the subject from which the drug X is eliminated faster? Fig 1 Ans a) Pharmacokinetics: The time course of the drug and metabolite concentrations in the body. b) (i) Subject A and B received the drug by an IV bolus (no Liberation and Absorption step) . Subject C received a dosage form wherein the drug had to be liberated from the dosage form and been absorbed into the blood. (Liberation and the Absorption step involved).(ii) In subject A the drug is eliminated faster. The plasma concentration fall faster in subject A when compared to subject B. 2) The table1 shows the serum concentration profiles of a certain drug in patient X. Please specify the units for the Pk parameters to get full credit. a) Determine if the elimination process is a first order or a zero order process. Plot the data on a semilog paper. b) Calculate Ke, the first order elimination rate constant. c) Calculate AUC 0-tlast and AUC 0-inf by trapezoidal rule. d) Calculate the concentration of the drug X in serum at time 5hr. Table 1 Time (hr) Conc.(ng/ml) 0 20 1 16.37 1.5 14.82 2 13.41 4 8.99 6 6.02 8 4.04 10 2.71 12 1.81 Ans) a) The elimination is a first order process. (plot of lnconc vs time is a straight line) hence plot on a semilog paper. 1.0010.00100.000 5 10 15Conc(mg/l)Time (hr)Serum conc vs Timeb) The equation is . Therefore the value of Ke = 0.2 hr-1 2.995 0.2 c) Time (hr) Conc.(ng/ml) AUC partial 0 20 1 16.37 18.19 1.5 14.82 7.80 2 13.41 7.06 4 8.99 22.39 6 6.02 15.01 8 4.04 10.06 10 2.71 6.74 12 1.81 4.52 AUC 0-tlast = 91.77 ng*hr/ml AUC tlast-inf =C12/Ke=1.81/0.2=9.05 ng*hr/ml AUC 0-inf = 91.77 + (1.81/0.2) = 100.82 ng*hr/ml d) 2.995 0.2 5C(5hr) = 7.352ng/ml True or False: 1) Therapeutic Drug Monitoring (TDM) in individual patients is important for drugs with a narrow therapeutic index. True 2) When the change in amount of the drug in the body is related to the amount by the following equation ^0, where X is the amount of the drug at a given time t, then we say the elimination is a zero order process. True 3) The plasma concentration time profile of a certain drug is dependent on the dosage form.
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