Routes of Drug
Administration
Drug Absorption
 Absorption
is the process by
which a drug enters the
bloodstream without being
chemically altered or
 The movement of a drug
from its site of application
into the blood
Drug Absorption

Factors which influence the rate of
absorption





the physicochemical properties of the
drug
routes of administration
dosage forms
circulation at the site of absorption
concentration of the drug
Drug Absorption
 Mechanisms




of absorption
passive diffusion
filtration
endocytosis
active transport
Lipid-Water Partition Coefficient

The higher the lipid/water p.c. the
greater the rate of absorption
decrease the lipid/ water p.c
will increase polarity of a drug, by
increasing
ionization.

increase
the lipid/ water p.c.
Will decrease polarity of a drug,
suppression of ionization

Routes of Drug
Administration
 The
possible routes of drug
entry into the body may be
divided into two classes:
Enteral
Parenteral
Enteral Routes

Enteral - drug placed directly in the GI
tract:
 sublingual
- placed under the
tongue
 oral - swallowing (p.o.)
 rectum - Absorption through the
rectum
Sublingual/Buccal
Some drugs are taken as smaller
tablets which are held in the mouth
or under the tongue.
 Advantages


rapid absorption
avoid first-pass effect
Sublingual/Buccal
 Disadvantages


small doses
unpleasant taste of some drugs
First-pass Effect

The first-pass effect is the term
used for the hepatic metabolism
of a pharmacological agent when
it is absorbed from the intestine
and delivered to the liver via the
portal circulation.
First-pass Effect
Oral
 Advantages



Convenient - can be self- administered,
pain free, easy to take
Absorption - takes place along the whole
length of the GI tract
Cheap - compared to most other
parenteral routes
Oral

Disadvantages



Sometimes non-efficient - only
part of the drug may be
absorbed
Expose to first-pass effect drugs absorbed orally are
initially transported to the liver
via the portal vein
irritation to gastric mucosa nausea and vomiting
Oral

Disadvantages cont.



effect too slow for emergencies
unpleasant taste of some drugs
Not suitable to use in
unconscious patient
Rectal
Uses
1. unconscious patients and children
2. if patient is nauseous or vomiting
3. good for drugs affecting the bowel such
as laxatives
4. irritating drugs contraindicated
Parenteral Routes



Intravascular (IV)- placing a drug
directly into the blood stream
Intramuscular (IM) - drug injected into
skeletal muscle
Subcutaneous - Absorption of drugs
from the subcutaneous tissues
Intravenous
Absorption phase is zero
(100% bioavailability)
1.Precise and accurate onset of action,
2. large amounts can be given
3. High risk of adverse effects
e.g. risk of embolism
Intramuscular
• .Pain at injection sites for certain drugs
• Used for oily or suspension drugs
Subcutaneous
1. slow absorption
2. absorption is limited by blood flow,
Inhalation
1.gaseous and volatile agents and aerosols
2.rapid onset of action due to rapid reach
circulation
a.large surface area
b.high blood flow
Topical
•Mucosal membranes (eye drops, antiseptic,
sunscreen,.)
•Skin
a. Dermal - ointment (local action)
b. Transdermal - absorption of drug through
skin (systemic action)
i. no first pass metabolism
e. g patches
Route for administration
-Time until effect







intravenous 30-60 seconds
inhalation 2-3 minutes
sublingual 3-5 minutes
intramuscular 10-20 minutes
subcutaneous 15-30 minutes
rectal 5-30 minutes
Oral 30-90 minutes
transdermal (topical) variable (minutes to
hours)
Experiment
:1
30 md/kg of
phenobarbital
sodium to rats by
 Oral
 IP
 IM
Action: loss of righting
reflex, ataxia,
anasethia.
Record onset time and
Experiment:
2
Effect of route of drug
administration
on drug action:
Magnesium sulphate
• I.P 1.0 gm/kg
sedation
• Oral 6.0 gm/kg
laxation