Biopharmaceutics and PK Lab 5Calculation of PK parameters usingone and two compartment model: IV bolus. Dr Sameh Rabea
Remember For 1st order kinetic one-compartment the equation will be: Cp= (Cp) 0 e –ktWhere: Cp: Y ; (Cp) 0 : intercept; t: X; k: -slope x 2.303; Slope= (logC2 – logC1)/t2-t1.Or Ke = ln (C1/C2)/t2-t1 The PK model: I.V. Central Ke injection Compartment Out. AUC= Cp0/ Ke Vdc= Dose/ Cp0. t ½= 0.693/ Ke.
For 1storder kinetic two-compartment the equation will be: Cp= A e –αt + B e –βt Where A: intercept of line 1 and B intercept of line 2; α: distribution rate constant and β: elimination rate constant.
The PK model: I.V. in Central K12 Peripheral Compartment Compartment inj. K 21 K2Cp0= A + BK2 = Cp0 / ( A/ α + B/ β )K12= A.B (β- α) 2 / Cp0 (A β + B α)K21= A β + B α / Cp0 .
AUC= A/α + B/β . t ½= 0.693/ β. Vd c= Dose/Cp0= Dose/ A+B. Vd area= Dose/AUC. β Vd ss = Vdc + (K12/K21) Vdc Vd tissue= Vd area – Vdc. Therefore: Vd area> Vd ss > Vdc> Vd tissue. But Vd ss is not affected by elimination, so its represents true volume of distribution. CL = Vdc. Ke or CL= Vdc. Β.
Problem # 1 A patient received 500 mg cefepime I.V bolus injection and numerous blood samples were drawn as the following: