1. PHARMACOKINETIC

2. PHARMACOKINETICS
How long it takes for a drug to reach the blood circulation
How long it takes for a drug to reach its site of action
How long a drug stays at its site of action
The dose needed to produce an adequate concentration of drug at its site of action
How often a dose must be given to maintain an adequate concentration of drug at its site of action

3. Definitions and Pharmacokinetic Terminology
Drug Absorption: the rate at which a drug enters the systemic circulation. Instantaneous for bolus intravenous administration
Bioavailability: F, the fraction of the dose that reaches the systemic circulation. F=1 for IV administration.
Absolute Bioavailability: Estimation of F for any other route in comparison to intravenous administration.
Relative Bioavailability: Estimation of F for a dosage form to another given by an extravascular (non-intravenous) route of administration.
Distribution: Movement of drug from the central compartment (tissues) to peripheral compartments (tissues) where the drug is present.
Elimination: The processes that encompass the effective "removal" of drug from "the body" through excretion or metabolism.

4. Definitions and Pharmacokinetic Terminology
Excretion: the removal of drug from the body by a physical process such as excretion into urine, bile, or sweat
Metabolism: the removal of drug from the body by metabolic transformation of the drug into other compounds. These processes include phase 1 (oxidative) or phase 2 (conjugative) metabolism
Volume of Distribution: the theoretical size (volume) of the space necessary to contain the amount of drug in the body given its concentration in specific fluids.
Clearance: the characterization of the volume which the body through elimination can completely remove all drug in a given period of time.
Half-Life: the length of time necessary to eliminate 50% of the remaining amount of drug present in the body

5. Definitions and Pharmacokinetic Terminology
Steady-State: the equilibrium condition reached when the amount of drug put into the kinetic system over time exactly equals the amount of drug eliminated by the system over that same period of time. (rate in = rate out)
Concentration: the measurement of the amount of drug contained in a specific volume of a biological fluid, typically plasma or urine. Cp
Maximum Concentration: the highest OBSERVED concentration from those included as the measurements of the time course of drug. Cmax
Time of Maximum Concentration: the time at which the highest concentration is measured from those included as the measurements of the time course of drug. Tmax
Area Under the Curve: the integration of drug concentration measurements over time using calculus. AUC0-∞ AUC0-24 AUC0-t

6. Pharmacokinetic Models
Clinical Pharmacokinetics
Pharmacokinetic Models
&
Concentration-time Profiles

7. one-compartment model & zero-order kinetics
A- You have a 10ml of orange squash. Put this into a 990ml of water
maximum
plateau
Amount in
water
Speed rise
water
Volume of distribution (Vd) = 1000

8. B- Each minute, empty 10ml of the orange liquid,discard this
and replace it with 10ml of water. Co
10 ml/min
5 ml/min
2.5 ml /min
Amount in
water
t1/2
water

9. One compartment model, first-order kinetics
This is a single compartment model,
That would occur if the bloodstream
was the only compartment in the body
(or if the Vd = the blood volume)
One compartment model, first-order kinetics

10. Apparent volume of distribution: the volume of fluid in which a drug would need to be dissolved to have the same concentration in that volume as it does in plasma
The Clearance (Cl) of a drug is the volume of plasma from which the drug is completely removed per unit time
The fraction of the drug in the body eliminated per unit time is determined
by the elimination constant (Ke)
Elimination half life (t1/2): the time taken for plasma concentration to reduce by 50%
Vd=amount of drug in the body
plasma drug concentration
Cl= rate of elimination of drug
*example:
Vd=1000 ml
Cl= 10 ml/min
t1/2=70 min
Ke=0.01
Cl = Ke x Vd
t1/2= 0.693/Ke

11. drug half-life

12. two-compartment model & zero-order kinetics
Why does a patient wake up after 5 minutes after an injection of thiopentone when we know that it takes several hours to eliminate this drug from the body?
What happens is that, initially the drug is all in the blood and this blood goes to "vessel rich" organs; principally the brain. After a few minutes the drug starts to venture off into other tissues (fat, muscle etc) it redistributes, the concentration in the brain decreases and the patient wakes up! The drug thus redistributes into other compartments.

13. C- This time put this orange squash into a beaker which has
a connection with an other one
equilibrium with the second
compartment
steady state
rapid rise

14. D- Again, each minute, empty 10ml of the orange liquid,discard this and replace it with 10ml of water
rapid fall
slower gradual fall
plateau

15. plateau
Semi-logarithmic graph of blood concentration versus time
alpha () phase: rapid redistribution phase, the alpha phase
plateau: equilibrium phase (where blood concentration = tissue concentration)
beta () phase: the elimination phase (where blood and tissue concentrations
fall in tandem)

17. Concentration profile depends on
Route of Administration
– Intravenous (bolus, infusion)
– Extravascular (oral, IM, SQ)
– Specialized
Disposition of the drug (ADME)
– distribution
– metabolism
– elimination

18. concentration-time profile
Curve generated by:
1. measuring drug concentration in plasma at time intervals after administration
2. plot drug concentration against sampling time
Absorption
Distribution
Elimination
Metabolism
Excretion
Usualy absorption of a drug from any site, is much more rapid than elimination from the systemic circulation

19. Cpmax: maximal plasma concentration
tmax: the time at which the maximal
plasma concentration occured
AUC: area under curve
After a single dose of drug is administered, the plasma concentration increasesas the drug is absorbed, reaches a peaks absorption is completed, and then declinesas the drug is eliminated

20. rate versus extent of absorption (rate varies)
A>B>C

21. rate versus extent of absorption (extent varies)
A>B>C (extent)
A=B=C (rate)
tmax

22. instantenous absorption?
i.v
oral,i.m,sc

23. other administration routes?
i.m>sc>oral

24. multiple dosing and drug accumulation
To maintain a pharmacological effect for a prolonged period, repeated dosing is necessary.
HOWEVER
If the interval between repeated doses is <4 drug halflives,drug accumulation will occur.
Drug has not been eliminated before next dose.
1 x t1/2 = 50% remaining
2 x t1/2 = 25% remaining
3 x t1/2 = 12.5% remaining
4 x t1/2 = 6.25% remaining

25. Steady-state concentration
Multiple dosing at 4 x t1/2 or less, drug accumulates until a steady-state concentration where;
rate of elimination = rate of absorption/distribution

26. Steady-state concentration

27. Why plasma concentration-dose graphics?
Toxic levels
Drug plasma concentration
Therapeutic levels
Sub-therapeutic levels