Routes of Drug Administration

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)
  
•  1^st 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 1^st 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

    1^st 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 1^st 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.