This document provides an overview of pharmacology and drug absorption. It defines pharmacology as the science of drugs and describes pharmacokinetics as what the body does to drugs and pharmacodynamics as what drugs do to the body. The key parameters of pharmacokinetics - absorption, distribution, metabolism and excretion - are explained. Drug absorption mechanisms like passive diffusion, carrier-mediated transport and active transport are summarized. Factors affecting drug absorption like solubility, concentration and route of administration are also highlighted. The document concludes by defining bioavailability and bioequivalence.

1. Basics of Pharmacology
Date: 12/07/2023
Presented by:
Deepak Jagdish Askar
B. Pharm., M. Pharm., Ph.D (Pursuing)
Panjab University, Chandigarh

2. What is pharmacology?
• Pharmakon meaning “Drug” and Logos meaning “ Science”.
• Pharmacokinetic: Pharmakon- Drug and Kinetics- Movement
What the body does to the drug?
• Pharmacodynamic: Pharmakon - Drug and Dynamics- Power
What the drug does to the body?
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4. Pharmacokinetics parameter are :
1. Absorption: is the movement of the drug from its site of administration to the
systemic circulation.
2. Distribution: is the movement of the drug from the systemic circulation to the
target site and the other tissues.
3. Metabolism: also known as ‘Biotransformation’- Chemical alteration of the drug
in the body.
4. Excretion: is the passage out of systemically absorbed drugs.
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5. Biological membrane
• The plasma membrane consists of a bilayer of amphipathic lipids
with their hydrocarbon chains oriented inward to the centre of the
bilayer to form a continuous hydrophobic phase and their
hydrophilic heads oriented outwards.
• The cell membrane is bilayer and having 100Ao thick.
• It is made up of phospholipids, cholestrol, proteins and
carbohydrates.
• Polar groups are (phospholipids head) oriented at the two surfaces
and with non-polar (hydrocarbon tails) embedded in the matrix to
form a continuous sheet.
• This makes it electrically resistant and relatively impermeable.
• Their specific lipid and protein composition differs according to
cell/ organelle type.
• Hydrophobic nature means lipid loving- good permeability
property.
• Hydrophilic nature means water loving- good solubility property.
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7. Mechanisms of drug absorption
• Broadly it is classified as:
A. Tanscellular/Intracellular transport
B. Paracellular/Intercellular transport
C. Vesicular transport
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Mechanism of drug transportation
Passive diffusion
Carrier mediated
diffusion
Facilitated
diffusion
Active transport
Primary AT
Secondary AT
Endocytosis
Phagocytosis
Pinocytosis
Filtration

10. • The movement or translocation of drug from one side of the biological barrier to the other is called as
Biotransport and the mechanisms underlying the transfer of a drug across the biological barriers are
called as the transport mechanisms.
• At all the levels whether a drug is absorbed, distributed, metabolized or excreted, it has to pass across
the cell membrane.
Passive diffusion:
It is a non-ionic or simple diffusion processes.
It is a transfer process in which the drug molecules pass through a biological barrier from the phase of
higher concentration to the phase of lower concentration without requiring any ependiture of energy by
the biological system.
Non-electrolytes (i.e. nonionised drugs) can diffuse passively across the biological barriers at a rate
proportional to their lipid water partition co-efficient.
It means the drugs that are highly lipid soluble can diffuse rapidly whereas those that are less lipid
soluble will diffuse more slowly.
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11. • Many drugs are weak acids or bases that are present in the solution as both the non-ionized and
ionized species.
• Non-ionized molecules-more lipid soluble- can diffuse readily across the cell membranes.
• Ionized molecules- less lipid soluble- less able to penetrate the membrane.
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12. • The conditions which favour the neutral (non-ionised) form of the drug will enhance the drug
permeation (absorption).
• The conditions that favour ionisation will restrict the translocation of weak electrolytes, since the
proportions existing as the diffusible (nonionised) form is low. This leads to a phenomenon called
as ‘ion-trapping’.
• For example:
The ionised form of weakly acidic drugs (aspirin;pKa 3.5) which crosses the gastric mucosa (pH 2),
reverts to the ionised form within the cell (pH 7) and hence, slowly passes to the extracellular fluid.
This type of ‘ion trapping’ possibly also contributes to gastric mucosal cell damage caused by aspirin.
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13. Carrier-mediated transport
• Polar compounds such as sugars and amino acids and certain drugs of therapeutic interest
cannot penetrate membranes by passive diffusion but are moved by carrier systems present on
the membrane surface.
• These carrier molecules, which are usually proteins, combine with the drug substrate in
question and form a complex.
• This drug- carrier complex exhibits better permeability than the drug alone.
• After the drug carrier complex crosses the membrane, the carrier dissociates from the drug.
• The carrier then either returns to the original side of the membrane for reuse or is essentially
produced on one side and eliminated at the other sides.
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14. Active transport (Up hill transport)
• Active transport of drugs as a energy dependent, carrier mediated transport of drugs as a energy-
dependent, carrier mediated transport taking place against the electrochemical gradient (Electrical
as well as concentration gradient).
• The energy needed for the active transport is generated by the membrane ATPase.
• The process of active transport can be blocked by inhibiting cell metabolism or by reducing the
ATP levels by giving agents like sodium cyanide, sodium fluoride or 2,4-dinitrophenol.
• In a similar manner, the drugs or substrate, having similar physico-chemical characteristics can also
compete for the same carrier-mediated active transport process.
• It is also a capacity limited process and it is also depends upon the availability of the carrier.
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15. • The mechanism of transport by endocytosis involves the cellular uptake of exogenous molecules or
complexes, inside plasma membrane derived vesicles.
1. Phagocytosis (Uptake of particles)
2. Pinocytosis (fluid uptake)
Filtration process
• The free or unbound drugs(or metabolite) of smaller molecules size can pass through the pores or
spaces between the cells by the process of filtration.
• It is a purely a physical process where the rate of filtration is propotional to a pressure gradient.
• This is an important mechanism for drugs of small molecular size which are filtered through
glomerulus.
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16. ABSORPTION
• The process of movement of drug into the bloodstream from its site of administration is called as
Absorption.
1. Absorption via GI tract
The absorption of drugs from GIT is mainly by passive diffusion through the lipid sheath.
Few drugs are too smaller to diffuse through the pores in the cell membrane while uptake of sugar
and other nutrients is by active transport.
The gut is more impermeable to non-ionised lipid soluble form of drug and less permeable to the
ionised form.
The ability of a drug to be absorbed via GIT and to reach the systemic circulation is compromised
as a result of drug loss due to: metabolism in these cells and liver, by vomiting, by disease that may
affect drug absorption.
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17. From Mouth-
• Saliva pH is slightly acidic but the pH of stimulated saliva reaches 7.4 (alkaline). Hence, lipid soluble( non-
ionised) basic or neutral drugs can be absorbed from this site.
• After the sublingual absorption, the drug directly goes into systemic circulation bypassing first pass
metabolism.
From Stomach-
• pH acidic. Unionised acidic or neutral drugs are absorbed from this site.
From Intestine-
pH alkaline.It is having a larger surface area hence it is a major site of absorption. Unionised basic or neutral
drugs are absorbed from this site. The drugs have to pass through hepatic portal system before going to systemic
circulation hence there are chance of first pass effect.
From large intestine or colon-
pH alkaline. Unionised basic or neutral drugs are absorbed from this site. From external haemorrhoidal vein,
the major amount of the drug goes directly to the systemic circulation hence minimal first pass effect.
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18. 2. Absorption via lungs
• Lipid soluble drugs when given in a vapourised form (general anaesthetics) or as aqueous solutions
spray or as spray of suspended microfined particles are absorbed by simple diffusion from the
pulmonary epithelium and the mucous membrane of trachea and lungs.
• Absorption is rapid because of the large surface area and high vascularity.
• First pass metabolism is avoided.
3. Absorption via topical sites
Absorption of most drugs through the intact skin is of course poor as the keratinised epidermis
behaves like a barrier to permeability. However, the underlying dermis is quite permeable to many
lipid soluble drugs and hence, significant absorption can occur if the skin is abraded.
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19. • Absorption via Parenteral sites
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20. • Factors affecting absorption are:
1. Aqueous solubility
2. Concentration
3. Area of absorbing surface
4. Vascularity of the absorbing surface
5. Routes of drug administration
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21. Bioavailability of drugs
• Bioavailability is defined as the rate at which and the extent to which the active
concentration of the drug is available at the desired site of action (i.e. in the blood
stream)
• It is a measure of fraction of administered dose of a drug that reaches the systemic
circulation in the unchanged form. It is considered that bioavailability of drug
injected i.v. is 100% but it is frequently lower after oral ingestion because -
Incomplete absorption and due to hepatic metabolism.
• Incomplete bioavailability after s.c. or i.m injection is less common but may occur
due to local binding of the drug.
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22. • Bioequivalent- Two preparations of a drug are considered bioequivalent when the
rate and extent of bioavailability of the drug from them is not significantly
different under suitable conditions.
• Chemical equivalent - Oral formulations of a drug from different manufacturers or
different batches from the same manufacturer may have the same amount of the
drug is chemically equivalent.
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23. • References
• KD Tripathi - Essentials of Medical Pharmacology
• HL Sharma and KK sharma
• The Pharmacological Basis of Therapeutics, Goodman and Gillman’s
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24. Self study is the promoting factor for the self growth.
THANK YOU!
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