DRUG ADMINISTRATION ROUTE

The administration route of a drug has a significant influence on the absorption of that drug.The administration route determines the time gap between when it is administered and the action taking place.The time between which a drug is administered and a response developed is the biological lag.
Medicine Direct notes two common routes of drug administration:

  • Oral or enteral and
  • Parenteral route

 

Oral Route
This has the following advantages:

  • It is a safe, appropriate and economical.
  • One can self-medicate.
  • The drug can be withdrawn

The following are the disadvantages:

  • Drug response is slow
  • Difficult to administer bitter drugs
  • Difficult to administer drugs that cause nausea
  • Gastric enzymes can render it inactive
  • Not feasible for an unconscious patient.

 

Oral Preparations

  • Pills and tablets that are enteric coated:

The coating is done with gluten or cellulose acetate.Acid juice in the stomach cannot destroy the coatings, thus inactivation of drug in the stomach is avoided.
However, alkaline intestinal juice can remove these coatings.

  • Spansules:

These are time or sustained release preparations in various coatings.Each coating tends to dissolve at different intervals.Thus the drug release is slowed for a protracted time.


Parenteral Route
These are any other routes other than enteral (oral).
It has the following advantages:

  • Fast absorption
  • Drug is given in proper dose
  • The drug goes into circulation active
  • It is used in emergencies
  • Can be used for unconscious patients

 

Disadvantages:

  • Pain from injection
  • Injection abscess procedures
  • Injection sterile procedures
  • It is costly
  • Cannot be self-administered

 

Parenteral Administration

  • Injection
  • Inhalation
  • Transcutaneous route
  • Transmucosal route
  • New drug delivery systems

 

Injection

  • Intradermal, e.g. B.C.G vaccine injected in skin layers.
  • Subcutaneous, for injecting non-irritant substance with even and slow absorption rate.
  • Intramuscular, for injecting into muscle tissue with uniform and speedy absorption rate.
  • Intra-arterial, for injecting into an artery.

If the proper artery is chosen, the drug effect can be localized in a specific organ.These routes are sometimes used for anticancer drugs.

  • Intraperitoneal, for injecting into the peritoneal cavity so that, fluids like glucose and saline can be administered to kids.
  • Bone – marrow, related to intravenous injection.

This is used when veins are unavailable because of thrombosis or circulatory collapse.
For kids, the femur or tibia is selected while for adults, the sternum for injection.

  • Intravenous, injecting directly into a vein.

 

Intravenous Advantages:

  • The drug is active as it goes into circulation.
  • Wanted blood concentration is achieved.
  • The rapid and instant effect is produced.
  • Useful for emergencies and unconscious patients.

 

Intravenous Disadvantages:

  • Drugs that precipitate blood components cannot be used.
  • Unpleasant reactions are immediate.
  • Drug withdrawal not possible.

Inhalation
This works for Gases, aerosols or vapours, and volatile liquid.

Advantages:

  • Instant drug absorption.
  • Localization of the effect in respiratory tract diseases.

 

Disadvantages:

  • Reduced dose regulation ability.
  • Local respiratory tract irritation may escalate its secretions.
  • The administration method is not easy.

 

Transcutaneous Route
This can be further classified into:

  • Iontophoresis
  • Inunctions
  • Jet injection and
  • Adhesive units.

 

Iontophoresis:
To use this method, one has to drive the drug deep into the skin with the use of a galvanic current like salicylates.
For a positively charged drug, anode iontophoresis can be used and for a negatively charged compound, cathode iontophoresis can be used.

Inunction:
Here the drug is rubbed on the skin.
The skin absorbs it and then a systemic effect is produced.
An example is the nitroglycerine ointment for angina.

Jet injection:
This method is painless as it does not need a spring.
It makes use of an instrument in a gun shape using a micro-fine orifice.
A dermojet (a high-velocity jet) is used to project the drug solution.

Adhesive units:
An example is a scopolamine for motion sickness.

 

 Transmucosal Route
This is classified as:

  • Sub-lingual
  • Trans-nasal
  • Trans-rectal

Sub-lingual route:
Here the drug is placed under the tongue till it is fully dissolved in the mouth.
An example is an isoprenaline and nitroglycerine.
It has the following advantages:

  • The onset of action is fast.
  • Terminates the effect of spitting tablet.
  • Drug inactivation in the stomach is prevented.
  • There is no inactivation in the liver as the drug goes directly into systemic circulation.

Trans-nasal route:

Trans-rectal route:
It has some advantages:

  • Gastric irritation is evaded.
  • Used by the elderly and terminally ill.

 

 New Drug Delivery Systems
Occusert:
It is administered under the eyelid, releasing drugs like pilocarpine for protracted periods.

Progestasert:
This is an intrauterine contraceptive ploy.
It creates controlled progesterone release inside the uterus for 12 months.

Pro-drug:
This drug is initially inactive, and then after administration, it becomes an active drug.
I-dopa compound, for example, is inactive.
When it is administered, it metabolizes to an active drug: dopamine.
It is an active drug for Parkinson.

Local application:
Drugs can be locally applied for onset action in a particular area.
The drugs can be in powder form, ointment, drops, lotion or paste.
They can be applied in the urethra and rectum, vagina, conjunctiva and the nasal mucous membranes.
There are certain preparations used for local applications:

  • Urethra uses a bougie.
  • Vagina uses a pessary.
  • Vagina and rectum use suppository.
  • Rectum uses enemata.