Routes of drug administration are the medium through which the drug is introduced into the body to show its pharmacological action or for diagnosis. They are generally classified by the location at which the substance is applied or based on the target of action is. Route of administration and dosage form are the main aspects of drug delivery.
Routes of Drug Administration - Overview
I. Systemic Route of Administration
Systemic Route of administration of drug involves the entry of a drug into the circulatory system which is further distributed to the whole body
It includes both enteral and parenteral route of administration.
A. Enteral Route of Administration
Enteral administration is the involvement of the gastrointestinal tract and is further classified as follows:
i) Oral Administration
It is the first choice for the administration of drugs. It is designated as Per Os (PO), which means to administer by mouth. The absorption of drugs administered by this route is determined by the physiological state of the GI tract.
Types of dosage forms administered through this route include pills, tablets, capsules, solutions, suspensions, emulsions, syrups, elixir, etc.
Advantages
Most Convenient and cost-effective.
Safest and painless.
Self-administered.
No sterilisation required.
Disadvantages
Not suitable for an emergency as the onset of action is slow.
Not suitable for unconscious patients, uncooperative and unreliable patients.
For drugs with extensive first-pass metabolism, this route is not used.
Unpalatable and highly irritant drugs are not suitable.
ii) Buccal or Sublingual Administration
Sublingual administration involves placing the drug under the tongue. Buccal administration involves placing the pill between the gums and cheek wherein both the cases, the drug is absorbed into the blood.
The types of dosage forms for this route include tablets, troches and lozenges. Ex: Nitroglycerin.
Advantages
Economic & Quick drug absorption.
Bypassing the first-pass metabolism.
Quick termination-spit off.
Self-administered.
Increased bioavailability.
Disadvantages
Not suitable for bitter and irritating drugs.
High doses can't be taken.
Less patient compliance.
Highly ionic drugs can not be administered.
iii) Rectal Route
Rectal medicines are administered through the anus, into the rectum.
The types of dosage forms for this route include suppositories and enemas
Ex: Prednisolone enema, indomethacin, diazepam.
Advantages
It avoids the first-pass metabolism.
Suitable for children and old age.
It is used for unconscious and vomiting patients.
Irritating drugs are contraindicated..
Disadvantages
Absorption is slow and erratic.
Not well accepted by patients.
Inconvenient.
B. Parenteral
The word parenteral is derived from Greek words para means outside and enter on means the intestine. These are the injection or infusion through a needle or catheter into the body. This route helps bypass the alimentary canal. They are classified as follows:
i) Inhalational
Inhaled medications can be absorbed rapidly and act both systemically and locally. A proper technique with inhaler devices is necessary to achieve the correct dose. Total size absorbed is variable.
Nasal Inhalations, Inhalation by smoking a substance is likely the most rapid way to deliver drugs to the brain, as the substance travels directly to the brain without being diluted in the systemic circulation. The severity of dependence on psychoactive may increase with more rapid drug delivery.
Advantages
May be used for local or systemic effects.
Disadvantages
Particle size of drugs determines anatomic placement in the respiratory tract.
May stimulate cough reflex.
Some drugs may be swallowed
ii) Injections
The injection is the act of putting a liquid, especially a drug, into a person's body using a needle (usually a hypodermic needle) and a syringe.
Injections are classified as follows:
a. Subcutaneous
The drug is deposited just beneath the skin in the loose subcutaneous tissue. As it is less vascular, absorption is slow, so prolonged action is produced. Only small volumes can be injected.
The needle is injected into the pinched skin at 90-degree angle and do this quickly without force. If you have very little fat, then inject at a 45-degree angle.
In addition to injection, it is also possible to slowly infuse fluids subcutaneously in the form of hypodermoclysis.
A subcutaneous route is used for protein drugs because such drugs would be destroyed in the digestive tract if they were taken orally.
Certain drugs (progestins for hormonal birth control) may be given by inserting capsules under the skin.
Advantages
Onset of action is faster than oral route.
Disadvantages
Sterile technique is needed.
More expensive.
Some drugs can irritate tissue and cause pain.
Only small volumes must be administered.
Various forms of SC route are:
- Dermojet: It is a needleless injection system with a high-pressure jet injector. A high velocity of drug solution is projected from a fine micro orifice using a GUN like an implant; the solution passes through the superficial layers and gets deposited in the subcutaneous tissue. It is nearly painless and suitable for mass inoculations. E.g. Insulin.
- Pellet: Drug in the form of solid pellet is introduced with TROCHAR and CANNULA .which provides sustained release of drug for weeks and months without repeated administration. E.g. DOCA, TESTOSTERONE.
- Sialistic (non biodegradable or biodegradable): Crystalline drug is packed in tubes or capsules and implanted under the skin. Slow and uniform release of drug for months with constant blood levels (non biodegradable drug have to be removed later). E.g. hormones and contraceptives like “NoRPLANT”.
b. Intravenous
Method of administering medications directly into the vein using a needle.it is the best way to deliver a precise dose quickly and in a well-controlled manner throughout the body. Drugs are delivered immediately into the bloodstream and tend to take effect more quickly than any other route.hence it is of great value in an emergency.
A 25 gauge needle 2 cm long with 25-degree angle is inserted into the skin. It is also used for irritable solutions which cause pain and damage to tissues if given by subcutaneous or intramuscular injection.
A solution containing a drug may be given in a single dose, or continuous infusion from a collapsible plastic bag or infusion pump through thin, flexible tubing inserted to the vein, usually a forearm.
Vital organs like heart, brain etc. get exposed to high concentrations of the drug.
Advantages
Rapid onset of action.
It bypasses the GI and first-pass metabolism.
Useful for drugs which are irritant to intramuscular route.
Disadvantages
Administered by trained person.
Accidental overdose can have serious consequences.
Limited to highly soluble drugs.
Break skin barrier.
c. Intramuscular
The drug is injected into one of a large skeletal muscle-triceps, rectus femoris, etc. It is a preferred route when larger volumes of a drug product are needed. It is more vascular; hence absorption is faster and less painful. The angle for IM is 90 degrees.
DEPOT preparations (oily solutions and aqueous suspensions) can be injected by this route.
Muscle permits the tissue to receive a larger volume of medication (deltoid and biceps maximum of 3ml).
NOTE: IM injections should be avoided in anticoagulant treatment patients as it can produce Local HAEMATOMA.
Advantages
Can administer larger volumes.
Technically easier than IV.
GI and first-pass metabolism are involved.
Disadvantages
Break the skin barrier.
Produce anxiety.
Painful.
d. Intradermal
The drug is delivered in the upper layer of the skin to the dermis, where the absorption is low. The angle for ID is 5 to 15 degrees with a needle placed almost flat to the skin.
It is the common method used for allergy testing.
Injections are made with fine short needles (26 gauge) and a small barrel syringe.
Advantages
Absorption is low, advantage for allergy testing.
Disadvantages
Amount of drug administered must be small.
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Needle Insertion Angles |
e. Intra Arterial
Intra Arterial injection or infusion is a method of delivering a drug directly into arteries to localise its effect to a particular organ/region while minimising the exposure of the body to potentially toxic effects of the agent.
Advantages
Used in chemotherapy to target drug organs.
Disadvantages
Drugs may be distributed to other tissues or organs.
f. Intra Articular
It is the injection which is directly delivered into the joints to relieve pain and swelling. Most of the anti-inflammatory drugs for arthritis treatment are given by this route.
Advantages
High concentration is obtained in localized areas.
Rapid onset of action.
Disadvantages
Sepsis and joint damage may occur on repeated drug administration.
g. Intrathecal
Intrathecal administration is a route for drugs via an injection into the spinal canal, or into the subarachnoid space so that it reaches the cerebrospinal fluid (CSF) and is useful in spinal anaesthesia, chemotherapy & pain management applications.
Advantages
Drugs act directly on meninges and CNS.
Bypass BBB & Blood-CSF barrier.
Disadvantages
Painful procedure.
Expertise needed.
iii) Transdermal
Transdermal administration is a route wherein active ingredients are delivered across the skin for systemic distribution of the drug. E.g. Transdermal patches. The drug is administered in the form of a patch or an ointment that delivers the drug into the circulation for systemic effect.
The absorption rate may vary. It is slow. Increased absorption with occlusive dressings. Formulations and devices for transdermally administered substances include:
Transdermal pathways are those by which drugs can cross the skin and reach the systemic circulation. Ex: Transcellular pathway, Intercellular pathway, Microneedles.
The more direct route used is known as the transcellular pathway.
Advantages
The transdermal delivery system (patch) is easy to use and withdraw.
Continuous release of the drug is observed for a specified period of time.
It is used for lipid-soluble drugs with a low dose and low molecular weight.
Low pre-systemic metabolism.
Disadvantages
Some irritation by patch or drug.
Permeability of skin is variable with the condition, anatomic site, age and gender.
Type of cream or ointment base effects the drug release and absorption.
II. Local Route of Drug Administration
These can only be used for localised lesions at accessible sites and for drugs whose systemic absorption from these sites is minimal.
High concentrations are attained at desired sites without exposing the rest of the body.
The local routes are:
A. Topical Route of Administration
The topical route includes: skin, eyes, or other specific membranes, the intranasal, inhalation, intravaginal and transdermal routes may be considered enteral or topical according to different definitions.
The medication is applied directly to the body surfaces, including the skin and mucous membranes of eyes, ears, nose, vagina and rectum.
Ex: Antibiotics, hormones, narcotics and chemotherapeutics.
B. Deeper Tissues
Few deeper areas can only be approached using a needle and syringe by this type of drug administration, but the drug should be in such a form that systemic absorption is slow and minimal.
Ex: Hydrocortisone acetate in the knee joint(intra-articular).
The retrobulbar injection which is a hydrocortisone acetate).
Lidocaine (Intrathecal injection).
C. Arterial Supply
Local but parenteral route attained by drug with minimal systemic absorption. The close intra-arterial injection is used for contrast media in angiography.
Anti-cancer drugs can be infused in femoral or bronchial arteries to localise the effect for limb malignancies. In these cases, the drug is injected into the artery, i.e., supplying the blood to the desired site.
Types of Dosage Forms Used for Different Routes
References
DM Brahmankar & SB Jaiswal, Biopharmaceutics and Pharmacokinetics - a Treatise, Vallabh Prakasham, Delhi.
Basic Pharmacokinetics by Hedaya, CRC press.
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