ROUTES OF ADMINISTRATION

❓. Describe the routes of drug administration. Their merits and demerits with suitable example? 

➡ Drugs can be administered by a variety of routes. The choice of an appropriate route depends both on the drug as well as patient-related factors.

Routes of drug administration can be classified into two major categories as follows:

1. Systemic

a. Oral

b. Sublingual

c. Rectal

d. Cutaneous

e. Inhalation

f. Parenteral

2. Local

a. Topical

b. For deeper tissues

c. Arterial supply

Systemic routes

Drugs intended to directly enter the bloodstream and distributed all over the body through circulation including the site of action are administered systemically.

Various systemic routes of drug administration are as follows:

a. Oral route

Drugs available in solid dosage forms like capsules, spansules, dragees,powders, tablets and liquid forms like elixirs, syrups, emulsions can be given orally

Merits

i. Safer

ii. More convenient

iii. Noninvasive and painless

iv. Assistance not required

v. Cheap

vi. May be destroyed by gastric juices, or amount is considerably reduced

in first-pass metabolism.

Demerits

i. Action is slower, not suitable for emergencies.

ii. Unpalatable drugs are difficult to administer.

iii. Can cause nausea or vomiting, may stain the teeth, leave an unpleasant taste.

iv. Certain drugs may not be absorbed, e.g. streptomycin.

b. Sublingual route

Here the tablet or pellet is placed under the tongue. Drug is directly

absorbed into the circulation. Example: Glyceryl trinitrate,

buprenorphine, desamino-oxytocin

Merits

i. First-pass metabolism is bypassed.

ii. Once desired effect is achieved the drug can be spat out.

iii. Rapid rate of absorption

Demerits

i. Only lipid-soluble nonirritating drugs can be used.

ii. Inconvenient to the patient.

c. Rectal route

Certain irritant and unpleasant drugs can be put into the rectum as suppositories or retention enema for systemic effect. 

For example:Aminophylline, indomethacin, diazepam and ergotamine are a few of them.

Merits

i. Used in patients having recurrent vomiting.

ii. Bypass first-pass metabolism.

Demerits

i. Highly inconvenient and embarrassing

ii. Absorption is slow and unpredictable.

iii. May cause rectal inflammation.

d. Cutaneous route

Highly lipid-soluble drugs are applied over the skin for low and prolonged action. First-pass metabolism in the liver is also bypassed. Drug can be incorporated in an ointment and applied over specific areas of the skin. For example: Betamethasone (Betnovate-C) 

Transdermal patches

i. These are the recent devices in the form of adhesive patches of various

shapes and sizes which deliver the drug at a constant controlled rate into the systemic circulation.

ii. The drug is held in between an occlusive backing film and a rate controlling micropore membrane whose undersurface is smeared with adhesive impregnated with priming dose of drug that is protected by another film to be peeled off just before application.

iii. The drug is absorbed percutaneously.

iv. Usual sites of application are chest, abdomen, upper arm, lower back, behind the ear, buttock and mastoid region. 

For example: Glyceryl trinitrate, fentanyl, nicotine, and oestradiol

Merits

i. Rate of drug delivery is constant.

ii. Patient compliance is better.

iii. Interindividual variations are reduced.

iv. Provides smooth plasma concentrations without fluctuation.

Demerits

i. Mild irritation and erythema is possible that can be overcome by

changing the site.

e. Inhalation

Volatile liquids and gases are given by this route for systemic effects. 

For example: General anaesthetic agents

Merits

i. Quick onset of action.

ii. Very less dose is required.

iii. We can regulate the amount of drug administered.

Demerits

i. Local irritation leading to increased respiratory secretions and bronchospasm.

f. Parenteral route

Refers to drugs injected directly into tissue fluid or blood without having to cross the intestinal mucosa.

Merits

i. Drug action is faster and surer.

ii. Gastric irritation and vomiting is not provoked.

iii. Can be used in unconscious, uncooperative patients.

iv. First-pass metabolism is bypassed in the liver.

Demerits

i. Chances of systemic toxicity are very high compared to the other routes.

ii. Invasive, painful procedure

iii. Preparations have to be sterilized and are costlier.

iv. Assistance of another individual required in most cases.

Various routes of parenteral drug administration are as follows:

i. Subcutaneous

ii. Intramuscular

iii. Intravenous

iv. Intradermal

• Subcutaneous

i. The drug is injected into the loose subcutaneous tissue that is rich in

nerve supply but is less vascular.

ii. Special forms of administration in this route are as follows:

a. Dermojet: Needle is not used. Essentially painless procedure. High velocity jet of drug solution is projected from microfine orifice using gun-like implement and the solution passes through superficial layers and gets deposited in the subcutaneous layer.

b. Pellet implantation: Solid pellet is introduced with a trochar and canula. It provides sustained release of drug over weeks, e.g. DOCA, testosterone.

C. Silastic implants: Crystalline drugs packed in biodegradable or nondegradable tubes or capsules implanted under the skin for slow uniform leaching of the drug, e.g. norplant for contraception.

Merits

1. Self-administration is possible.

2. Repository (depot) preparations can be inserted into subcutaneous tissue.

Demerits

1. Not suitable for emergency as absorption is slow.

2. Suitable only for nonirritant drugs.

• Intramuscular

i. Drugs are injected into larger skeletal muscles like deltoid, triceps,

gluteus, rectus femoris, etc.

ii. A volume of 5-10 mL can be given at a time. For example: Tetanus

toxoid, procaine penicillin.

Merits

i. Absorption is more rapid as the muscles are more vascular.

ii. Depot preparations can be administered by this route.

Demerits

i. Aseptic conditions are needed.

ii. Self-administration is impractical as deep penetration is necessary.

iii. They may cause injury to the nerves.

• Intravenous

i. Drugs are injected directly into the bloodstream through a vein.

ii. Drugs are injected as bolus or infused slowly over hours into

superficial veins.

Merits

Merits

i. This route of drug administration is of great value in emergencies as the

drug directly enters blood stream and effects are produced

immediately.

ii. 100% bioavailability, dosage of drug required is lesser.

Demerits

i. Most risky route.

ii. Vital organs like brain, heart, etc. get exposed to higher concentrations of the drug.

iii. Systemic toxicity is increased.

iv. Once injected the action of the drug cannot be halted.

•Intradermal

Injected into the skin raising a bleb or scarring or multiple puncture of the epidermis through a drop of the drug is done. For example: BCG vaccine, sensitivity tests.

Local routes

They can be used only for localized lesions at accessible sites and for drugs whose systemic absorption from these sites is minimal, slow or absent.

High concentration is attained at the desired site without exposing the rest of the body to the adverse effects or toxicity of the drug.

1. Topical

• Refers to external application of the drug to the surface of the localized

lesion.

• Can be used to deliver the drug to skin, oropharyngeal or nasal mucosa,

eyes, ear canal, anal canal, vagina, etc.

Examples:

1. Inhalation for bronchial mucosa (cromolyn sodium)

2. Irrigating solution or jellies (povidone iodine, lignocaine)

3. Paints, toothpastes, mouthwashes, gargles, lozenges, antiseptics,

astringents, haemostatics

2. Deeper tissues

• Can be approached with a syringe and needle.

• Care should be taken to see that the systemic absorption is slow.

Examples: Injection of local anaesthetic around a nerve, intra-articular injection of hydrocortisone acetate

3. Arterial supply

Close intra-arterial injections can be used for a contrast media in angiography and anticancer drugs used in the femoral or brachial artery to localize the effect for limb malignancies.