Routes of Drug Administration (Enteral, Parenteral, Topical)
I. Enteral Routes: Placement of drug directly into any part of the GIT is called an 'enteral' mode of administration
a) Oral: Swallowing a drug through mouth
Advantages:
- Most commonly used method as it is safe, convenient & painless procedure
- Economical as sterilization of drug products is not essential
- No need of any assistant
Disadvantages:
- Onset of action is slower
- Polar drugs can't be given as they are not absorbed (eg: Streptomycin)
- Drugs are destroyed by the digestive juices (Eg: Penicillin-G, Insulin, Oxytocin)
- 1st pass effect (those destroyed in liver before reaching systemic circulation) (eg: Morphine, Isoprenaline)
- Bad test & Bad smell & irritant drugs can't be given
- Drugs can't be given to unconscious & uncooperative patients
- Drugs can't be given during emesis
b) Sublingual / Buccal
The drug is place beneath the tongue (sublingual) or crushed in mouth and spread over the buccal mucosa (Buccal).
Advantages:
- Quick onset of action because of rapid absorption due to more blood supply in that region
Bypasses the portal circulation
- no 1st pass metabolism
Drug action can be terminated at any time when side effects are observed
Disadvantages:
- Distasteful, irritant drugs can't be given
- Higher molecular weight drugs can't be absorbed (eg; insulin)
Examples
Isosorbide dinitrate tablets & Nitroglycerin tablets (for Angina), Isopranline sulfate tablets (for Bronchial Asthma), Nifedipine in powder form (in Hypertension)
c) Rectal: Through Rectum (Suppositories, Enema)
Advantages:
Useful in patients with nausea and vomiting
1st pass metabolism is greatly bypassed as a major portion of the drg is absorbed from external haemorrhoidal veins
Useful for gastric irritant drugs
Disadvantages:
Chances of rectal inflammation
Absorption is irregular
Inconvenient and embarrassing to the patient
Examples
Dulcolax & Glycerine suppositories, enemas, ointments for Local action
Aminophylline (Bronchodillator) & Indomethacin (Anti-inflammatory agent) Suppositories for Systemic action
II. Parenteral Routes:
Routes other than "Enteral" are called 'Parenteral' routes of administration. Administration of drugs by injection, by topical application to skin or by inhalation through the lungs are all parenteral.
a) Intravenous:Through lumen of the veins
Advantages:
Directly enters into the systemic circulation & no 1st pass effect & quicker onset of action
Less dose is needed to achieve greater therapeutic effects
Valuable in emergency
Can be given evening unconscious, uncooperative patients those are having nausea, vomiting & diarrhea
Hypertonic solutions & GIT irritant drugs can be infused
Large volume of fluids can be infused at a uniform rate
Amount of the drug can be controlled with an accuracy
Disadvantages:
Strict aseptic conditions are needed
Patient has to depend upon other person for administration of drug
Painful
Risky because once the is injected it can't be recalled
Introduction of any air or particulate matter produce embolism which is fatal
Drugs in suspensions & Oily drugs can't be given
Depot injections can's be given
Venous thrombosis & Thrombophlebitis of the vein injected
Necrosis around the site of action
Examples: Glucose, Glucose normal saline, Dopamine & Norepinephrine drips
b) Intramuscular
Deltoid muscle or gluteal mass of left or right buttock
Vastus muscle underlying the lateral surface of the thigh
Advantages:
Absorption is more predictable, less variable & rapid compared to Oral route
Depot injections can be given
Disadvantages:
Perfect aseptic conditions are needed
Chances of abscess at the site of injection
Chances of nerve damage leading to paresis of muscle supplied by it
Large volumes can't be given (maximum 5 – 10 ml)
Examples: Depot injection of Testosterone, Antibiotics, Antiemetics
c) Intraperitoneal
Into the peritoneal space
Rapid absorption due to large surface area
Painful, risky
Antirabies injection can be given
d) Intrathecal (Intraspinal)
Into the subarachnoid space
They crosses BBB & Blood CSF barrier
Strict aseptic conditions & grater expertise is needed
Its painful & risky procedure
Many radiopaque contrast media for myelography (to visualize spinal cord) are given through this route
Xylocaine injection for providing Spinal Anesthesia
e) Intramedullary:
Injection into the tibial or sternal bone marrow
f) Intra-arterial:
into the lumen of the desired artery
g) Intra-articular: injection directly into the joint space
h) Subcutaneous: Injection into the subcutaneous tissue under the skin
Inhalation: Inspiration through nose or mouth
III. Topical Routes
a) Transdermal
Transdermal Patches
In these adhesive patches, the drug is incorporated into a polymer (usually Polyisobutylene) which in turn is bonded to an adhesive plaster
The drug is delivered at the skin surface by diffusion, for percutaneous absorption into circulation
These preparations are designed to provide steady & smooth plasma concentration of the drug for a period ranging from 1-3 days from the site of their application
Site of application: Chest, Abdomen, Upper arm or Mastoid region
Examples: Transdermal Patches of Nitroglycerine, Scopalamine, Clonidine, Estradiol
For diagram refer KD Tripathi Text book
b) Conjuctival: into the conjuctiva for local effects eg: Sulfacetamide
c) Vaginal and Urethral: Pessaries are used for local actions
d) Inunction (Rubbing): rubbing onto the skin
Newer Drug Delivery Systems: To improve drug delivery and to prolong its duration of action, special drug delivery systems have recently been developed.
These include: Ocuserts, Progestaserts, Transdermal Adhesive Patches, Prodrugs, Computerised Miniature Pumps, Use of Monoclonal Antibodies and Liposomes as drug carriers.
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