ROUTES OF DRUG ADMINISTRATION

Most of the drugs can be administered by different routes. Drug- and patient-related factors determine
the selection of routes for drug administration. The factors are:
1. Characteristics of the drug.
2. Emergency/routine use.
3. Site of action of the drug—local or systemic.
4. Condition of the patient (unconscious, vomiting, diarrhoea).
5. Age of the patient.
6. Effect of gastric pH, digestive enzymes and first-pass metabolism.
7. Patient’s/doctor’s choice (sometimes).
Routes

Local Systemic
General Pharmacology

Enteral Parenteral
– Oral – Inhalation
– Sublingual – Injections
– Rectal – Transdermal

Local Routes
It is the simplest mode of administration of a drug at the site where the desired action is required.
Systemic side effects are minimal.
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 2 Routes of Drug Administration

1. Topical: Drug is applied to the skin or mucous membrane at various sites for local action.
a. Oral cavity: As a suspension, e.g. nystatin; as a troche, e.g. clotrimazole (for oral candidiasis);
as a cream, e.g. acyclovir (for herpes labialis); as ointment and jelly, e.g. 5% lignocaine
hydrochloride (for topical anaesthesia); as a spray, e.g. 10% lignocaine hydrochloride (for
topical anaesthesia).
b. GI tract: As tablet that is not absorbed, e.g. neomycin (for sterilization of gut before
surgery).
c. Rectum and anal canal:
i. As an enema (administration of drug into the rectum in liquid form):
– Evacuant enema (for evacuation of bowel): For example, soap water enema—soap acts
as a lubricant and water stimulates the rectum.
– Retention enema: For example, methylprednisolone in ulcerative colitis.
ii. As a suppository (administration of the drug in a solid form into the rectum), e.g.
bisacodyl— for evacuation of bowels.
d. Eye, ear and nose: As drops, ointments and sprays (for infection, allergic conditions, etc.), e.g.
gentamicin eye/ear drops.
e. Bronchi: As inhalation, e.g. salbutamol, ipratropium bromide, etc. (for bronchial asthma and
chronic obstructive pulmonary disease).
f. Skin: As ointment, cream, lotion or powder, e.g. clotrimazole (antifungal) for cutaneous
candidiasis.
2. Intra-arterial route: This route is rarely employed. It is mainly used during diagnostic studies such
as coronary angiography and for the administration of some anticancer drugs, e.g. for treatment
of malignancy involving limbs.
3. Administration of the drug into some deep tissues by injection, e.g. administration of triamcinolone
directly into the joint space in rheumatoid arthritis.

Systemic Routes
Drugs administered by this route enter blood and produce systemic effects.

Enteral Routes
It includes oral, sublingual and rectal routes.

Oral Route
It is the most common and acceptable route for drug administration. Dosage forms are tablet, capsule,
General Pharmacology

syrup, mixture, etc., e.g., paracetamol tablet for fever, omeprazole capsule for peptic ulcer are given orally.
Advantages
z Safer.

z Cheaper.

z Painless.

z Convenient for repeated and prolonged use.

z Can be self-administered.

Disadvantages
z Not suitable for emergency as onset of action of orally administered drugs is slow.

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Routes of Drug Administration
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z It is not suitable for/in:

U Unpalatable and highly irritant drugs.

U Unabsorbable drugs (e.g. aminoglycosides).

U Drugs that are destroyed by digestive juices (e.g. insulin).

U Drugs with extensive first-pass metabolism (e.g. lignocaine).

U Unconscious patients.

U Uncooperative and unreliable patients.

U Patients with severe vomiting and diarrhoea.

Sublingual Route
The preparation is kept under the tongue. The drug is absorbed through the buccal mucous membrane
and enters the systemic circulation directly, e.g. nitroglycerin for acute anginal attack and buprenorphine
for myocardial infarction.
Advantages
z Quick onset of action.

z Action can be terminated by spitting out the tablet.

z Bypasses first-pass metabolism.

z Self-administration is possible.

Disadvantages
z It is not suitable for:

U Irritant and lipid-insoluble drugs.

U Drugs with bad smell and taste.

Rectal Route
Drugs can be given in the form of solid or liquid.
1. Suppository: It can be used for local (topical) effect (see p. 4) as well as systemic effect, e.g.
indomethacin for rheumatoid arthritis.
2. Enema: Retention enema can be used for local effect (see p. 4) as well as systemic effect. The drug is
absorbed through rectal mucous membrane and produces systemic effect, e.g. diazepam for status
epilepticus in children.

Parenteral Routes
Routes of administration other than enteral route are called parenteral routes.
General Pharmacology

Advantages
z Onset of action of drugs is faster; hence it is suitable for emergency.

z Useful in:

U Unconscious patient.

U Uncooperative and unreliable patients.

U Patients with vomiting and diarrhoea.

z It is suitable for:

U Irritant drugs.

U Drugs with high first-pass metabolism.

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 2 Routes of Drug Administration

U Drugs not absorbed orally.

U Drugs destroyed by digestive juices.
Disadvantages
z Require aseptic conditions.

z Preparations should be sterile and is expensive.

z Requires invasive techniques that are painful.

z Cannot be usually self-administered.

z Can cause local tissue injury to nerves, vessels, etc.

Inhalation
Volatile liquids and gases are given by inhalation for systemic effects, e.g. general anaesthetics.
Advantages
z Quick onset of action.

z Dose required is very less, so systemic toxicity is minimized.

z Amount of drug administered can be regulated.

Disadvantages
z Local irritation may cause increased respiratory secretions and bronchospasm.

Injections (Fig. 1.1)

Intradermal route: The drug is injected into the layers of the skin, e.g. Bacillus Calmette–Guérin
(BCG) vaccination and drug sensitivity tests. It is painful and only a small amount of the drug can
be administered.
Subcutaneous (s.c.) route: The drug is injected into the subcutaneous tissues of the thigh, abdomen
and arm, e.g. adrenaline, insulin, etc.

Intradermal

Subcutaneous

Intravenous

Intra-arterial
General Pharmacology

Intramuscular

Intra-articular

Fig. 1.1 Injectable routes of drug administration.

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Routes of Drug Administration
2

Advantages
z Self-administration is possible (e.g. insulin).

z Depot preparations can be inserted into the subcutaneous tissue, e.g. norplant for contraception.

Disadvantages
z It is suitable only for nonirritant drugs.

z Drug absorption is slow; hence it is not suitable for emergency.

Intramuscular (i.m.) route: Drugs are injected into large muscles such as deltoid, gluteus maximus
and vastus lateralis, e.g. paracetamol, diclofenac, etc. A volume of 5–10 mL can be given at a time.
Advantages
z Absorption is more rapid as compared to oral route.

z Mild irritants, depot injections, soluble substances and suspensions can be given by this route.

Disadvantages
z Aseptic conditions are needed.

z Intramuscular injections are painful and may cause abscess.

z Self-administration is not possible.

z There may be injury to the nerves.

Intravenous (i.v.) route: Drugs are injected directly into the blood stream through a vein. Drugs are
administered as:
1. Bolus: Single, relatively large dose of a drug injected rapidly or slowly as a single unit into a vein.
For example, i.v. ranitidine in bleeding peptic ulcer.
2. Slow intravenous injection: For example, i.v. morphine in myocardial infarction.
3. Intravenous infusion: For example, dopamine infusion in cardiogenic shock; mannitol infusion in
cerebral oedema; fluids infused intravenously in dehydration.
Advantages
z Bioavailability is 100%.

z Quick onset of action; therefore, it is the route of choice in emergency, e.g. intravenous diazepam to

control convulsions in status epilepticus.

z Large volume of fluid can be administered, e.g. intravenous fluids in patients with severe dehydra-

tion.
z Highly irritant drugs, e.g. anticancer drugs can be given because they get diluted in blood.

z Hypertonic solution can be infused by intravenous route, e.g. 20% mannitol in cerebral oedema.

z By i.v. infusion, a constant plasma level of the drug can be maintained, e.g. dopamine infusion in

cardiogenic shock.
Disadvantages
General Pharmacology

z Once the drug is injected, its action cannot be halted.

z Local irritation may cause phlebitis.

z Self-medication is not possible.

z Strict aseptic conditions are needed.

z Extravasation of some drugs can cause injury, necrosis and sloughing of tissues.

z Depot preparations cannot be given by i.v. route.

Precautions
z Drug should usually be injected slowly.

z Before injecting, make sure that the tip of the needle is in the vein.

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 2 Routes of Drug Administration

Intrathecal route: Drug is injected into the subarachnoid space (spinal anaesthetics, e.g. lignocaine;
antibiotics, e.g. amphotericin B, etc.).
Intra-articular route: Drug is injected directly into the joint space, e.g. hydrocortisone injection for
rheumatoid arthritis. Strict aseptic precautions should be taken. Repeated administration may cause
damage to the articular cartilage.
Transdermal route: The drug is administered in the form of a patch or ointment that delivers the
drug into the circulation for systemic effect (Fig. 1.2).
For example, scopolamine patch for sialorrhoea and motion sickness, nitroglycerin patch/ointment
for angina, oestrogen patch for hormone replacement therapy (HRT).
Backing layer
D D D D
D D D Drug reservoir
D D D D
D D D D D Rate controlling
membrane
Adhesive layer

Outer layer, which is

peeled off before
application to skin

Fig. 1.2 Transdermal drug-delivery system.

General Pharmacology

Key Points for Dentists

° Read the label of the drug carefully before administering a drug to the patient.
° Strict aseptic precautions should be taken while giving injections.
° Care should be taken to avoid needle-stick injuries, which may transmit infections, e.g. human immunode-
ciency virus (HIV), hepatitis B, hepatitis C, etc.

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 II. Routes of Drug Administration

ROUTE OF ABSORPTION ADVANTAGES DISADVANTAGES

ADMINISTRATION PATTERN
Oral • Variable; affected by many • Safest and most common, • Limited absorption of some drugs
factors convenient, and economical • Food may affect absorption
route of administration
• Patient compliance is necessary
• Drugs may be metabolized before
systemic absorption

Intravenous • Absorption not required • Can have immediate effects • Unsuitable for oily substances
• Ideal if dosed in large volumes • Bolus injection may result in adverse
• Suitable for irritating substances effects
and complex mixtures • Most substances must be slowly
• Valuable in emergency situations injected
• Dosage titration permissible • Strict aseptic techniques needed
• Ideal for high molecular weight
proteins and peptide drugs

Subcutaneous • Depends on drug diluents: • Suitable for slow-release drugs • Pain or necrosis if drug is irritating
Aqueous solution: prompt • Ideal for some poorly soluble • Unsuitable for drugs administered in
Depot preparations: suspensions large volumes
slow and sustained

Intramuscular • Depends on drug diluents: • Suitable if drug volume is moderate • Affects certain lab tests (creatine
• Suitable for oily vehicles and certain kinase)
Aqueous solution:
prompt irritating substances • Can be painful
Depot preparations: • Preferable to intravenous if patient • Can cause intramuscular
slow and sustained must self-administer hemorrhage (precluded during
anticoagulation therapy)

Transdermal • Slow and sustained

(patch) • Bypasses the first-pass effect • Some patients are allergic to
• Convenient and painless patches, which can cause irritation
• Ideal for drugs that are lipophilic and • Drug must be highly lipophilic
have poor oral bioavailability • May cause delayed delivery of drug
• Ideal for drugs that are quickly to pharmacological site of action
eliminated from the body • Limited to drugs that can be
taken in small daily doses
Rectal • Erratic and variable • Partially bypasses first-pass effect • Drugs may irritate the rectal
• Bypasses destruction by stomach acid mucosa
• Ideal if drug causes vomiting • Not a well-accepted route
• Ideal in patients who are vomiting, or
comatose
• Absorption is rapid; can have • Most addictive route (drug can
Inhalation • Systemic absorption may immediate effects
occur; this is not always enter the brain quickly)
desirable • Ideal for gases • Patient may have difficulty
• Effective for patients with respiratory regulating dose
problems • Some patients may have
• Dose can be titrated difficulty using inhalers
• Localized effect to target lungs: lower
doses used compared to that with
oral or parenteral administration
• Fewer systemic side effects

• Bypasses first-pass effect • Limited to certain types of drugs

Sublingual • Depends on the drug:
• Bypasses destruction by stomach
Few drugs (for example, • Limited to drugs that can be
acid taken in small doses
nitroglycerin) have rapid,
direct systemic absorption • Drug stability maintained because • May lose part of the drug dose if
the pH of saliva relatively neutral swallowed
Most drugs erratically or
incompletely absorbed • May cause immediate pharmacologi-
cal effects

Figure 1.5
The absorption pattern, advantages, and disadvantages of the most common routes of administration.

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