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Routes of Drug Administration
Dr. Haji Bahadar
• Factors affecting route
• Local Routes and their advantages and
• Enteral Routes and their advantages and
• Parenteral Routes and their advantages and
• A route of administration is the path by
which a drug is given to the body.
Factors affecting the choice of
1. Physical and chemical properties of the drug
2. Site of desired action
3. Rate and extent of absorption from different
4. Effect of digestive juices and first pass
metabolism on the drug
5. Rapidity with which the response is desired
6. Accuracy of dosage required
7. Condition of patient
• These can only be used for localised lesions at
accessible sites & for drugs whose systemic
absorption from these sites is minimal. E.g. GTN
applied as ointment
• High concentrations are attained at desired site
without exposing rest of body.
• The local routes are:
2. Deeper tissues
3. Arterial Supply
• This refers to external application of the drug to the surface
for localized action.
• (a) Skin: Drug is applied as ointment, cream, lotion
• (b) Mucous membrane: The dosage form depends on the
• (i) Mouth and pharynx: mouth washes, lozenges
• (ii) Eyes, ears and nose: As drops, ointments, irrigation,
• (iii)Gastrointestinal tract: As non-absorbable drugs given
orally e.g. aluminium hydroxide.
• (iv)Bronchi and lungs: As inhalations, aerosols (nebulised
solution or fine powder)- e.g. Salbutamol.
• (v) Urethra: As jellies e.g. Lidocaine.
• (vi)Vagina: vaginal tablets, cream.
• (vii) Rectum: As ointment, suppositories.
• Another local/ Parenteral route of
administration though invasive
• The drug is in such state that absorption is slow
and systemic absorption is minimal
• e.g. Hydrocortisone acetate in knee joint/
• Local but Parenteral route attained by drug with
minimal systemic absorption
• E.g. 1) Intra-arterial injection for contrast media
2)anti –cancer drugs in femoral artery/
brachial artery to localise malignancies in limbs
When drug is placed directly in the GI
• Oral administration is designated as Per Os (PO),
which means to administer ‘by mouth’.
• The medication is swallowed, and the drug is
absorbed from the stomach and small intestines.
Advantages of Oral admin.
• Safest route
• No skill required, self medication
• Painless, & acceptable
• Cost effective
• No maximal/strict sterilization
Disadvantages of Oral admin.
• Slow absorption delayed onset of
action Not suitable for emergencies
• Unpalatable and irritant drugs not
administered e.g. Chloramphenicol
• May cause nausea and vomiting
• Absorption of drugs variable and
erratic e.g. Streptomycin not absorbed
• Interactions of prescribed drug with food
and other drugs affects absorption
• Administration difficult in uncooperative
& unconscious patients
Disadvantages of Oral admin. – cont’d
• Some drugs are destroyed by gastric
secretions e.g. Insulin
• Some drugs are undergo extensive first
pass metabolism in the liver e.g.
• Some drugs are taken as smaller tablets which are held in the
mouth (buccal tablet) or under the tongue (sublingual
• Most commonly by suppository or enema.
• 2 types of enema:
i) Evacuant - e.g. soap water in rectum
ii) Retention- e.g. prednisolone enema in ulcerative colitis
1. By-pass liver - Some of the veins draining the rectum
lead directly to the general circulation, thus by-passing
the liver. Reduced first-pass effect by 50%.
2. Useful - This route may be most useful for patients
unable to take drugs orally (unconscious patients) or
with younger children Or in persons feeling nausea and
e.g. diazepam, paracetamol, Ergotamine, Indomethacin
Disadvantages of Rectal route
• Psychological, patient may be embarrassed
and dislike this way
• Irritation of mucosa & inflammation may
occur with repeated use
• Emergency (slow onset of action)
• Absorption unreliable, especially if rectum
is full of fecal matter
• Drug injected into the layers of skin raising a bleb
• e.g. BCG vaccine, allergy test
-small amount of drug injected
-may be painful
E.g. Insulin, Heparin
Patients can be trained for self-administration
Irritant drugs can cause severe pain- due to rich nerve supply
Less vascular tissue – slows absorption + if vasoconstriction is there then
further decreases absorption
Repeated injections at same site lipoatrophy decreased absorption
Highly vascular↑ absorption
Irritants, depot preparations, suspensions, colloids can be injected
Nerve liable to injury or irritation
Local infection with necrosis
Some drugs have decreased absorption by IM ( diazepam, phenytoin)
Some drugs should be avoided (heparin)
a) bolus- large dose dissolved in vehicle injected slowly e.g. Heparin
b) Slow injection- over 15-20 mins e.g. Aminophylline
c) Slow infusion- for constant plasma conc. About 1 litre soln infused for about 3-4 hrs
depending drug and patient conditions
-Immediate action ( useful in emergencies)
-Large volumes can be given
-Rapid adjustments possible
-Irritation of veins cause thrombophlebitis
-Extravasations of drug can cause irritation
-Only aqueous soln can given IV
Drug to be injected in the subarachnoid space for CNS action e.g. Spinal
Used for long duration surgeries to prevent complications from general
Direct and Rapid Action
N.B Strict aseptic conditions are required.
- Used for gaseous and volatile agents and aerosols.
A) Large surface area
B) Serves as local route in lung diseases
C) high blood flow
D) Hepatic first pass met. Is avoided
E) Small dose since direct delivery – less toxicity
- As result of that a rapid onset of action due to rapid
access to circulation.
• Most addictive route of administration because it hits the
brain so quickly.
• Difficulties in regulating the exact amount of dosage.
• Sometimes patient having difficulties in giving themselves
a drug by inhaler.
• Drug may induce cough e.g. Cromolyn sodium
• Pulmonary secretion may get enhanced