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Pharmacokinetics

objective is to describe time vs plasma
concentration profile of a drug



CHEE 440
evaluate performance of different dosage forms
adjust dosage regimens
ADME processes modeled by viewing body
as a series of interconnected compartments
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CHEE 440
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open one-compartment model


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process of distribution to each compartment is much
faster than absorption into blood and elimination
drug concentration everywhere in the compartment is
equal (CSTR)
elimination processes are pseudo-1st order
Vd
ka
D
CHEE 440
Cp
DB
kel
Du
Dm
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IV injection
dDB
 k el D B
mass balance :
dt
Cp  Cop exp k elt 

log Cp
time, t
CHEE 440
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Extravascular


tablets, capsules, transdermal...
most drugs absorbed by simple diffusion
DA 
DB 
DE
ka
k el
DoA k a
CP 
exp kel t   exp ka t 

Vd ka  k el 
CHEE 440
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Continuous infusion
k0
CP 
1 exp k el t 

Vd k el
Cp
time
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
biological half-life

time required to reduce amount of drug in body
to 1/2 original dose
0.693
t1 
2
k el

used to determine
fluctuation of plasma concentration between doses
 persistence of drug in system once drug
administration ceases

CHEE 440
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Dosing Schedule
MTC
Cp
MEC
time after administration
CHEE 440
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