routes of drug administration

1. Routes of Drug Administration
Dr. Haji Bahadar
PharmD, PhD,
KMU-IPMS

2. Contents
• Definition
• Factors affecting route
• Classification
• Local Routes and their advantages and
disadvantages
• Enteral Routes and their advantages and
disadvantages
• Parenteral Routes and their advantages and
disadvantages

3. Definition
• A route of administration is the path by
which a drug is given to the body.

4. Factors affecting the choice of
route
1. Physical and chemical properties of the drug
2. Site of desired action
3. Rate and extent of absorption from different
routes
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

5. Classification

6. Local Routes
• 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:
1. Topical
2. Deeper tissues
3. Arterial Supply

7. Topical route
• This refers to external application of the drug to the surface
for localized action.
• (a) Skin: Drug is applied as ointment, cream, lotion

8. Topical Route
• (b) Mucous membrane: The dosage form depends on the
site :
• (i) Mouth and pharynx: mouth washes, lozenges
(strepsil)
• (ii) Eyes, ears and nose: As drops, ointments, irrigation,
nasal spray.
• (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.

9. Deeper tissues
• 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/
retrobulbar injection

10. Arterial Supply
• Local but Parenteral route attained by drug with
minimal systemic absorption
• E.g. 1) Intra-arterial injection for contrast media
in angiography;
2)anti –cancer drugs in femoral artery/
brachial artery to localise malignancies in limbs

11. Enteral Routes
• Definition:
When drug is placed directly in the GI
tract.
Enteral
Oral
Buccal/
Sublingual
Rectal

12. Oral Route
• 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.

15. Advantages of Oral admin.
• Safest route
• Commonest
• Convenient
• No skill required, self medication
• Painless, & acceptable
• Cost effective
• No maximal/strict sterilization
required

16. 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

17. 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.
Lidocaine, testosterone

18. Sublingual/ Buccal
• Some drugs are taken as smaller tablets which are held in the
mouth (buccal tablet) or under the tongue (sublingual
tablet).

19. Rectal route
• 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
• ADVANTAGES
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
vomiting.
e.g. diazepam, paracetamol, Ergotamine, Indomethacin

20. 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

21. Parenteral- Injections
Injections
Intradermal
Intramuscular
Subcutaneous
Intravenous
Intraperitoneal
Intrathecal
Intra-arterial
Intrarticular

22. Intradermal
• Drug injected into the layers of skin raising a bleb
• e.g. BCG vaccine, allergy test
• Disadvantage
-small amount of drug injected
-may be painful

23. E.g. Insulin, Heparin
Advantages
Reliable
Patients can be trained for self-administration
Disadvantages
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
Subcutaneous (s/c)

24. Intramuscular Injection
Advantages
More reliable
Highly vascular↑ absorption
Irritants, depot preparations, suspensions, colloids can be injected
Disadvantages
Painful
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)

25. Intravenous injection
Given as
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
Advantages
-Immediate action ( useful in emergencies)
-100% bioavailability
-Large volumes can be given
-Rapid adjustments possible
Disadvantages
-Irritation of veins cause thrombophlebitis
-Extravasations of drug can cause irritation
-Only aqueous soln can given IV

26. Intrathecal
Drug to be injected in the subarachnoid space for CNS action e.g. Spinal
anaesthetics
Advantages
Used for long duration surgeries to prevent complications from general
anaesthesia
Direct and Rapid Action
N.B Strict aseptic conditions are required.

27. Inhalation
- Used for gaseous and volatile agents and aerosols.
Advantages
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.

28. Inhalation
Disadvantages
• 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