Nomenclature:Every drug has three names:
1) Chemical Name:
The drug is named according to its
chemical structure.
2) Generic name (common name):
Non proprietary name is assigned to the
drug to be easy to remember.
It should reflect some important pharmacologic
or chemical characteristics of the drugs.
3) Brand name (trade name):
Proprietary name is privately owned by the
manufacturer to distinguish certain drug
product from the other.
The name may have an indication to its
therapeutic use or the name of the
manufacture.
e.g. AspirinChemical name:Acetyl salicylic acidGeneric name:AspirinBrand name:RivoAspocidJuspirinAlexoprin
e.g. AcetaminophenChemical name:N-acetyl-p-amino phenolGeneric name:Acetaminophen (USP) or Paracetamol (BP)Brand name:AbimolParamolPanadol
e.g. KetoprofenChemical name2-(3-benzoylphenyl)propanoic acidGeneric name:KetoprofenBrand name:KetofanAlcofanProfenid
PharmacodynamicsHow do drugs act?
Drugs can produce their effects through one or more of the following mechanisms.
1) Drug-receptor interactions: The cells in certain tissue contain
structures called receptors. Receptors are macromolecules
component of the cell that bind the drug to produce a response.
Receptors are located at cell membranes or in the cell nucleus.
The drug is thought to fit onto a receptor like a key fits a lock.
The ability of the drug to bind to the receptor depends on the bond formed between the drug and the receptor.
[D] + [R] [DR] Response
Agonist:
A drug which can bind to
a receptor to produce a
response.
Antagonist:
A drug which bind to
receptor and produce no
effect (compete with the
agonist and inhibit its
effect).
2) Antimetabolites/cytotoxic:
Drug act by impairing cell reproduction.
This means that the affected cells may
remain alive and may continue to carry
out many of their functions, but are
unable to reproduce successfully, leading
to cell death (Methotrxate,
Cyclophosphamide).
The drug may resemble substances which are
used by the cells for nutrition and when
absorbed, the cells can not used them and so
failed to multiply.
The sulphonamides which are used to stop the
multiplication of bacteria are good example.
They are very similar in structure to para-
aminobenzoic acid and certain bacteria can not
distinguish between them and absorb the
sulphonamides and stop generation.
3) Action on enzymes:
Enzymes are substances which speed up
many chemical processes within the body.
Drugs may produce their effects through
inhibition or stimulation of certain enzymes.
Sulphonamides are used as antibacterial
agents as they inhibit folate synthase
enzyme so decrease the synthesis of folic
acid by bacteria death
4) Action on cell membrane:
The action of nerves and muscles
depends on ions passing across the
membranes surrounding these cells.
Certain drugs interfere with the
movement of these ions and thus prevent
nerve or muscle function (local
anaesthetics).
5) Chelating agents:
Adsorb drugs, electrolytes or biological
substances in the intestine to form non-
absorbable complex that is excreted in the
feces (Cholestyramine).
Activated charcoal is used as a non-specific
antidote in treatment of poisoning as it
adsorbs poisons on its surface and inhibit
their absorption from the GIT.
Pharmacokinetics
I. Drug Absorption
II. Drug Distribution
III.Drug Metabolism
IV. Drug Excretion
These factors
determine the drug
dose and frequency
of administration
I. Drug AbsorptionAbsorption is the transport of drug from the site of administration to the blood stream.Drugs must be librated and dissolved before it can be absorbed into systemic circulation.Absorption involves the passage of the drug across cell membranes.
II. Drug Distribution After the drug reaches the
blood stream, the drug is
distributed through the body
fluids and tissues.
Drugs exist in two forms: bound
and unbound (free) forms.
The protein-bound drug is
inactive and not subjected to
metabolism or excretion.
The binding capacity of plasma protein is limited.
Once saturation has been reached, a small increase in drug dose increase in free drug concentration pharmacological activity.
Competition of drugs for binding to plasma protein serious drug interactions.
Aspirin + Warfarin
Aspirin displaces warfarin from plasma protein
bleeding.