A seminar on one & two compartment open model extra vascular administration

1. A SEMINAR ON ONE & TWO
COMPARTMENT OPEN MODEL
EXTRA VASCULAR
ADMINISTRATION
PRESENTED BY
SANKAR DASARI
M PHARM ,PHCETS ,1 YR 2 SEM
MALLAREDDY COLLEGE OF PHARMACY
GUIDED BY
Dr. SATYA BRATA BHANJA sir

2. 2
Pharmacokinetic models are used to simplify all the
processes that occur during drug administration that
include drug distribution and elimination in the body.
Compartment models – Classical pharmacokinetic models
That stimulate the kinetic processes of drug A,D and E
Compartment models broadly categorised into two types
Single compartment model
One compartment model

Multiple compartment model which includes
Two compartment model
Three compartment model

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4. 4

5. 5

6. 6

7. One Compartment Open model extra
vascular administration can be shown
in a diagrammatic way by the
following diagram
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8. Normal and semi log plots depicting one compartment
open model extra vascular administration
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9. 9

10. In One Compartment open model
 EXTRAVASCULAR ADMINISTRATION
When drug is administered by extravascular route,
absorption is prerequisite for its therapeutic activity. The
rate of absorption may be described mathematically as
zero-order or first-order process.
After e.v. administration, the rate of change in the amount
of drug in the body is given by
dx = Rate of absorption – Rate of elimination
dt
dX = dXev - dxe
dt dt dt
10

11. • During absorption phase, the rate of absorption is
greater than elimination phase.
dXev > dxe
dt dt
• At peak plasma concentration,
dXev = dxe
dt dt
• During post absorption phase,
dXev < dxe
dt dt

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12. ZERO-ORDER ABSORPTION MODEL
R0 KE
Drug Blood Excretion
This model similar to that of constant rate infusion and
all equation which applies to it are applicable to this
model.
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13. FIRST-ORDER ABSORPTION MODEL
Ka KE
Drug Blood Excretion
first order
From equ. dX = dXev - dxe
dt dt dt
Differentiating above equ. We get,
dX = Ka Xa – KEX, Ka= absorption rate const.
dt Xa= amt of drug remaining
to be absorbed.
Integrating above equ.,
X =

[ ]
tKTK
Ea
oa aE
ee
KK
FXK
--
-
-)(
13

14. ABSORPTION RATE CONSTANT
This can be calculated by METHOD OF RESIDUALS.
Method is also known as Feathering, stripping and
peeling.
Drug that folllows one- compartment kinetics and
administered e.v. , the concentration of drug in plasma
is expressed by biexponential equation:


Assuming A = Log Ka F X 0
Vd (Ka – KE)

C = A e-kEt – A e-Kat

14

15. During the elimination phase, when absorption is most
over, Ka >>KE

C = A e-Ket
In log form above equation is

Log C = Log A - Ket
2.303

Where, C = back extraplotted plasma conc. Values.
Substracting true plasma conc. From extraploted one,
log(C – C ) =Cδ = Log A - Ket
2.303

15

16. 16

17. This method works best when difference between Ka
KE is large (Ka/KE >3)
If KE/Ka > 3 , the terminal slope estimates Ka and not
KE whereas the slope of residuals line gives Ke and not
Ka.
This is called as flip-flop phenomenon since the slopes
of the two lines have exchanged their meanings.
17

18. Wagner Nelson Method for Estimation of K
a

The method involves determination of k
a
from percent un absorbed- time plots
and does not required assumption of zero or first- order absorption
After oral administration of single dose of drug at any given time ,the amount
of drug in the body X and the amount of drug eliminated from the body X
E

.Thus:
X=V
d
C ,
The total amount of drug absorbed into systemic circulation from time zero to
infinite can be given as :
Since at t = ∞, ,the above equation reduce to :
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19. The fraction of drug absorbed at any time t is given as:
Percent drug unabsorbed at any time is therefore:


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21. Two compartment open model
extra vascular administration
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References:
1.D.M. Brahmankar, compartment model in
Biopharmaceutics and Pharmacokinetics, Vallabh
prakashan, second editon, 2009; p:
2.Applied Biopharmaceutics and Pharmaceutics
sixth edition
LEON SHARGEL