Introduction to Biopharmaceutics For Pharmacy students

1. Introduction
Biopharmaceutics
By: Assistant lecturer Bareq S. Mohammed
4th Stage students
Lecture (1)

2. Biopharmaceutics
• It is the study of how the physiochemical properties
of the drug, the dosage form (drug product), and the
route of administration affect the rate and extent of
systemic drug absorption.

3. Biopharmaceutics
• Thus, biopharmaceutics involves factors that
influence the following:
• 1. Protection and stability of the drug within the
product
• 2. The rate of drug release from the product
• 3. The rate of dissolution of the drug at the
absorption site
• 4. The availability of the drug at its site of action

4. Important terms
Absorption
• The process of movement of a drug from its site of
administration to the systemic circulation.
Bioavailability
• Defined as the rate and extent (amount) of drug
absorption, any alteration in a drug’s bioavailability is
reflected in its pharmacological effect.

5. Important terms
Drug distribution
The movement of the drug between one compartment
and the other (generally blood and extravascular tissue)
Drug elimination
Is the process that tends to remove the drug from the
body and terminates its action.
(metabolism) inactivates the drug
(excretion) exit of drug metabolite from the body.

6. ADME

9. Absorption of drugs
The process of movement of an unchanged drug from
the site of administration to the site of measurement
i.e. plasma.
Both the rate and the extent of drug absorption are
important. Such an absorption pattern has several
advantages:

10. Absorption of drugs

11. Cell membrane structure and physiology:

12. Mechanisms of drug absorption
1. Passive diffusion.
2. Pore transport.
3. Facilitated diffusion.
4. Active transport.
5. Ion pair transport.
6. Endocytosis.

13. Passive diffusion

14. Passive diffusion
Is defined as the difference in the drug concentration
on either side of the membrane.
Since no energy source is required the process is
called passive diffusion.

15. Fick’s low
States that the drug molecules diffuse from a region of
Higher conc. Lower conc.
until equilibrium is attained.

16. Fick’s low
dQ/dt = rate of drug diffusion (amount/time).
D = diffusion coefficient of the drug through the membrane (area/time)
A = surface area of the absorbing membrane for drug diffusion (area).
Km/w = partition coefficient of the drug between the lipoidal membrane and the
aqueous GI fluids (no units)
(CGIT – C) = difference in the concentration of drug in the GI fluids and the plasma,
called the concentration gradient (amount/volume).
h = thickness of the membrane (length)

17. Fick’s low
• when the drug is ingested, CGIT >> C and a large
concentration gradient exists thereby acting as the
driving force for absorption.
• Since under usual conditions of absorption, D, A,
Km/w, and h are constants, the term DAKm/w / h can
be replaced by a combined constant P called
permeability coefficient.

18. Fick’s low
• Permeability refers to the ability of the drug to
penetrate or diffuse through a membrane.
• As a result, the equation may be simplified to:

20. Introduction
Biopharmaceutics cont.
By: Assistant lecturer Bareq S. Mohammed
4th Stage students
Lecture (2)

21. Facilitated diffusion
• Carrier-mediated transport system that operates down
the concentration gradient (downhill transport)
• The driving force is the concentration gradient (hence
a passive process).
• No energy expenditure is involved.

22. Facilitated diffusion
• Examples
1. Entry of glucose into RBCs
2. Intestinal absorption of vitamins B1 and B2.

23. Active Transport
• Need energy in the form of ATP.
Active transport mechanisms are further subdivided
into
Primary–there is a direct ATP requirement.
transfers only one ion or molecule in only one
direction and hence is called a uniporter
e.g. absorption of glucose.

24. Active Transport
Secondary:
No direct requirement of ATP i.e. it takes advantage of
a previously existing concentration gradient.
The energy required in transporting an ion aids the
transport of another ion or molecule (co-transport)
either in the same direction or in the opposite direction.

26. Active Transport
Active transport is a more important process than
facilitated diffusion in the absorption of nutrients and
drugs and differs from it in several respects:
1. The drug is transported against the concentration
gradient
2. The process is faster than passive diffusion.
3. Energy expenditure is required.
.

27. Active Transport
Since the number of carriers is limited, the system is
capacity-limited i.e. at higher drug concentrations; the
system becomes saturated.

28. Pore Transport
• It is also called convective transport, bulk flow, or
filtration.
• This mechanism is through the protein channels
present in the cell membrane.
• Example, urea, water, and sugars.

29. Pore Transport

30. Ion-Pair Transport
• Example:
• Quaternary ammonium compounds + Mucin
• They are charged molecules, these drugs penetrate
membranes poorly. When linked up with an
oppositely charged ion, an ion pair is formed in which
the overall charge of the pair is neutral. This neutral
complex diffuses more easily across the membrane.
• Propranolol, a basic drug that forms an ion pair with
oleic acid, is absorbed by this mechanism.

31. Endocytosis
• It is a minor transport mechanism that involves
engulfing extracellular materials within a segment of
the cell membrane to form a vesicle (also called
vesicular transport) which is then pinched off
intracellularly

32. Endocytosis
• Endocytosis includes two types of processes:
1. Phagocytosis (cell eating): adsorptive uptake of
solid particulates
2. Pinocytosis (cell drinking): uptake of fluid solute.

33. Endocytosis

34. THANK YOU