2. In one compartment model with bolus dose in PK model, derive equation for concentration (C), half-life (t1/2), and clearance (ke) from mass-balance equation.
one compartment model with bolus dose in PK model is first order reaction
ke = elimination rate constant
Mass balance equation
Initial rate of dose available in body - rate of dose out = rate of change of dose with time
0 - ke*X = dX/dt
dX/dt = - ke*X
Relation between dose amount (X) and concentration of plasma (C)
X = C*V
V = Apparent volume of distribution
dX/dt = - ke*X
d(C*V) /dt = - ke*(C*V)
dC/dt = - ke*C
dC/C = - ke*dt
Integrate the equation
Initial concentration (at time t = 0) = Co
Final concentration (at time t = t) = C
ln (C/Co) = - ke*t
Half life (t1/2) is when the final concentration C = Co/2
ln [C/(C/2)] = - ke*t1/2
ln 2 = - ke*t1/2
t1/2 = - 0.6932 / ke
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