BASICS OF PHARMACOLOGY

PHARMACOLOGY

The term Pharmacology is derived from two Greek words Pharmacon meaning “drug” and
logos meaning “to study”.

Therefore, Pharmacology in simple terms defines as the study of drugs

Definition: Pharmacology can be defined as the study of the effects of drugs on the function
of living systems.

DRUG:

Drug is any chemical substance or product that is used or is intended to be used to modify or
explore physiological systems or pathological states for the benefit of the recipient.

Drug can be used for three purposes

i. Diagnosis of a disease/disorder: Ex. Fluorescein (A dye used in angiography or

angioscopy of the iris and retina.), Betazole (For use clinically to test gastric secretory
function.)
ii. Prevention of a disease: Ex. Vaccines
iii. Treatment / cure of a disease: Ex Paracetamol

SOURCES OF DRUGS

There are several sources of drugs

a) Plant Sources: Drugs can be obtained from various plant parts. Some of them are
i. Leaves: Some of the example of drugs obtained from leaves are
Digitalis purpurea - source of Digitoxin and Digoxin, which are cardiac glycosides.
Eucalyptus give oil of Eucalyptus, which is important component of cold & cough
syrup.
Tobacco leaves give nicotine.
Atropa belladonna gives atropine
ii. Flowers:
Poppy (Papaver somniferum) gives morphine (opoid)
Vinca rosea gives vincristine and vinblastine
iii. Fruits:
 Senna pod gives anthracine, which is a purgative.
Calabar beans give physostigmine, which is cholinomimetic agent.
iv. Seeds:
Nux Vomica give strychnine, which is a CNS stimulant.
Castor seeds give castor oil.
v. Roots:
Ipecacuanha root gives Emetine, used to induce vomiting as in accidental
poisoning. It also has amoebicidal properties.
Rauwolfia serpentina gives reserpine, a hypotensive agent. Reserpine was used for
hypertension treatment.
vi. Bark:
Cinchona bark gives quinine and quinidine, which are antimalarial drugs.
Quinidine also has antiarrythmic properties.
Atropa belladonna gives atropine, which is anticholinergic.
Hyoscyamus niger gives Hyosine, which is also anticholinergic.
vii. Stem:
Chondrodendron tomentosum gives tuboqurarine, which is skeletal muscle
relaxant used in general anesthesia.

b) Animal Sources: Drugs obtained from animals Ex. Human chorionic gonadotropin
(hCG) obtained from urine of Pregnant women which can be used for treatment of
infertility, Tyroxin from Sheep Thyroid, Vitamin A and Vitamin D from Cod Liver etc.
c) Mineral Sources: Some of the examples of drugs obtained from minerals are
Iron is used in treatment of iron deficiency anemia.
Mercurial salts are used in Syphilis (bacterial inf.).
Zinc is used as zinc supplement. Zinc oxide paste is used in wounds and in eczema.
Iodine is antiseptic. Iodine supplements are also used.
Gold salts are used in the treatment of rheumatoid arthritis
Fluorine has antiseptic properties.
Borax has antiseptic properties as well.
Selenium as selenium sulphide is used in anti-dandruff shampoos.
d) Microbial Sources:
Penicillium notatum is a fungus which gives penicillin.
Actinobacteria give Streptomycin.
 Aminoglycosides such as gentamicin and tobramycin are obtained from
streptomycis and micromonosporas.
e) Semisynthetic Sources: Partly obtained from natural sources and partly man-made Ex.
Apomorphine, Ampicillin
f) Synthetic Sources: Man-made drugs, drugs obtained by chemical synthesis Ex.
Antianxiety Drug, Anticonvulsant Drug
g) Recombinant DNA Technology: Drugs obtained through genetic engineering Ex.
Insulin

NOMENCLATURE/NAMING OF DRUG

1. Chemical Name
The name which reflects the chemical structure or composition of drug IUPAC Name
Ex. N-(4-hydroxyphenyl) acetamide
2. Non-Proprietary (Generic) Names
It is the original name the drug is given when the drug company applies for the approval
process Ex. Paracetamol or Acetaminophen
3. Brand Names or Trade Name
Name given by company which develops the drug. Ex. Crocin, Paradol, Dolo

ROUTES OF DRUG ADMINISTRATION (GENERAL)

Most drugs can be administered by a variety of routes. The choice of appropriate route in a
given situation depends both on drug as well as patient related factors.

Routes can be broadly divided into those for

(a) Local action and (b) Systemic action.

A. Local Routes (Local Action): These are the types of routes where the drugs intended to
used are not meant to reach into the blood circulation. Local routes can be given through
(a) Topical: The topical route includes application to the skin or to the mucous membrane
of the eye, ear, nose, throat, airway, or vagina for local effect.
(b) Deeper tissues: Certain deep areas can be approached by using a syringe and needle,
but the drug should be in such a form that systemic absorption is slow, e.g. intra-
articular injection (hydrocortisone acetate in knee joint), infiltration around a nerve or
 intrathecal injection (lidocaine), retrobulbar injection (hydrocortisone acetate behind
the eyeball)
(c) Arterial supply: Close intra-arterial injection is used for contrast media in
angiography; anticancer drugs can be infused in femoral or brachial artery to localise
the effect for limb malignancies.
B. Systemic Routes (Systemic Action): These are the types of routes where the drugs intended
to be used are meant to reach into the blood circulation. Systemic routes can be given
through
(a) Enteral: In this the drugs are delivered to the systemic circulation via Gastro Intestinal
Tract.
i. Oral (p.o): Drug is taken through the mouth, swallowed, and then
processed via the digestive system
ii. Sublingual/Buccal: The sublingual route involves placement of drug under
the tongue. The buccal route involves placement of drug between the cheek
and gum
iii. Rectal: The rectal route offers partial avoidance of the first-pass effect.
Larger amounts of drug and drugs with unpleasant taste are better
administered rectally than by the buccal or sublingual routes.
(b) Parenteral: This can be of
i. Inhalation: Route offers delivery closest to respiratory tissues (eg, for
asthma). Usually very rapid absorption (eg, for anesthetic gases). Volatile
liquids and gases are given by inhalation for systemic action.
ii. Transdermal: The transdermal route utilizes application to the skin for
systemic effect. Absorption usually occurs very slowly (because of the
thickness of the skin), but the first-pass effect is avoided.
iii. Injections: Drugs given to injections
a) Intradermal (i.d) The intradermal (ID) route involves injection into
the dermis, the more vascular layer of skin under the epidermis. Agents
for diagnostic determination and desensitization are usually
administered by this route
b) Intramuscular (i.m.) The drug is injected in one of the large skeletal
muscles—deltoid, triceps, gluteus maximus, rectus femoris, etc.
 Often faster and more complete (higher bioavailability) than with
oral administration. Large volumes may be given if the drug is not too
irritating. First-pass metabolism is avoided.
c) Subcutaneous (s.c): The drug is deposited in the loose subcutaneous
tissue which is richly supplied by nerves (irritant drugs cannot be
injected) but is less vascular (absorption is slower than intramuscular).
Like IM injection, SC injection provides absorption via simple
diffusion and is slower than the IV route. SC injection minimizes the
risks of hemolysis or thrombosis associated with IV injection and may
provide constant, slow, and sustained effects. This route should not be
used with drugs that cause tissue irritation, because severe pain and
necrosis may occur.
d) Intravenous (i.v.): The drug is injected as a bolus (Greek: bolos–lump)
or infused slowly over hours in one of the superficial veins.
Instantaneous and complete absorption (by definition, bioavailability is
100%). Potentially more dangerous.
e) Intraosseous infusion (i.o.) is the process of injecting medications,
fluids, or blood products directly into the marrow of a bone. It allows
placement of a drug directly into the cancellous bone adjacent to the
tooth to be anesthetized
ROUTES OF DRUG ADMINISTRATION (EYE)

1. Oral

2. Parenteral

3. Topical (most common) ex. Eye Drops, Eye Ointment/Gel

4. Subconjunctival Injections (antibiotics): a type of periocular route of injection for

ocular drug administration by administration of a medication either under the
conjunctiva or underneath the conjunctiva lining the eyelid.

5. Subtenon Injections: It involves administration of a medication to the area between

the sclera and the Tenon capsule.

6. Peribulbar/Retrobulbar Injection (lignocaine): Peribulbar injection is performed by

injecting the drug in the orbit around the equator of the eye ball (globe). The retrobulbar
route involves the insertion of a needle through the eyelid and orbital fascia to depose
the drug behind the globe into the retrobulbar space.

7. Intracorneal (stromal) (Voriconazole injections): Administration of a drug within the

eye cornea.

8. Intracameral (Anterior Chamber): An intracameral (IC) injection directly delivers

the drug into the anterior chamber of the eye.

9. Intra-vitreal (Vitreous): Intravitreal administration is done by injecting a drug

solution, suspension, or intraocular implants into the vitreous cavity.
Factors for choice of route of Drug administration
1. Physical and chemical properties of the drug (solid/ liquid/gas; solubility, stability, pH,
irritancy).
2. Site of desired action—localized and approachable or generalized and not approachable.
3. Rate and extent of absorption of the drug from different routes.
4. Effect of digestive juices and first pass metabolism on the drug.
5. Rapidity with which the response is desired (routine treatment or emergency).
6. Accuracy of dosage required (i.v. and inhalational can provide fine tuning).
7. Condition of the patient (unconscious, vomiting).