Easy Pharmacology

Routes of Drug administration

Enteral Others
1- Buccal e.g. Sublingual 1- Parenteral (Injection
2- Oral 2- Inhalation
3- Rectal 3- Topical
 I. ORAL ROUTE
* It is the most common and acceptable route for drug
administration. Dosage forms are tablet, capsule, syrup, mixture,
etc., e.g., paracetamol tablet for fever, omeprazole capsule for
peptic ulcer are given orally.
•Advantages:
- Convenient - portable, safe, no pain can be self-administered.
- Cheap - no need to sterilize (but must be hygienic of course)
- Variety of dosage forms available - fast release tablets, capsules,
enteric coated, layered tablets, slow release, suspensions,
mixtures
- Convenient for repeated and prolonged use.
•Disadvantages of oral route
- Sometimes inefficient: - high dose or low solubility drugs may
suffer poor availability, only part of the dose may be absorbed. -
First-pass effect: - drugs absorbed orally are transported to the
general circulation via the liver. Thus drugs which are extensively
metabolized will be metabolized in the liver during absorption. e.g.
the propranolol
-Food :- Food and G-I motility can effect drug absorption. Often
patient instructions include a direction to take with food or take on
an empty stomach.
- Local effect: - Antibiotics may kill normal gut flora and allow
overgrowth of fungal varieties. Thus, antifungal agent may be
included with an antibiotic.
- Unconscious patient: - Patient must be able to swallow solid
dosage forms. Liquids may be given by tube.
 II. BUCCAL and SUBLINGUAL ROUTE (SL)
• Some drugs are taken as smaller tablets which are held in the
mouth or under the tongue.
• These are buccal or sublingual dosage forms.
• Buccal tablets are often harder tablets [4 hour disintegration
time], designed to dissolve slowly.
Nitroglycerin, as a softer sublingual tablet [2 min disintegration
time], may be used for the rapid relief of angina.
• This Route of administration is also used for some steroids such
as testosterone and oxytocin. Nicotine containing chewing gum
may be used for cigarette smoking replacement.
 III. RECTAL ROUTE
• Drugs can be given in the form of solid or liquid.
- Suppository: It can be used for local (topical) effect as well as
systemic effect, e.g. indomethacin for rheumatoid arthritis.
- Enema: Retention enema can be used for local effect 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.
• Advantages of rectal route
- Used in children. - Little first pass effect.
- - Can be given in vomiting. - Can be given in unconscious
patient.
- - Higher therapeutic concentrations of drug are achieved rapidly
in rectum.
- - For rapid evacuation of bowel, usually during gut sterilization
before any surgical or radiological procedure.
• Disadvantages of rectal route
- Inconvenient, not well accepted. May be some
discomfort
- Drug absorption is slow and erratic.
- Irritation or inflammation of rectal mucosa can occur
 (Parenteral)
• Routes of administration other than enteral route are called
parenteral routes.
• Advantages of parenteral routes
- Onset of action of drugs is faster; hence it is suitable for
emergency.
- Useful in:
- Unconscious patient.
- Uncooperative and unreliable patients.
- Patients with vomiting and diarrhoea.
- It is suitable for:
- Irritant drugs. - Drugs with high first-pass metabolism.
- Drugs not absorbed orally.
- Drugs destroyed by digestive juices.
Disadvantages of parenteral routes
- Require aseptic conditions.
- Preparations should be sterile and is expensive.
- Requires invasive techniques that are painful.
- Cannot be usually self-administered.
- Can cause local tissue injury to nerves, vessels, etc
i. INTRAVENOUS (IV)
• Drugs may be given into a peripheral vein over 1 to 2 minutes or
longer by infusion, or Drugs are injected directly into the blood
stream through a vein.
• Drugs are administered as:
a) 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.
b) Slow intravenous injection: For example, i.v. morphine in
myocardial infarction.
c) Intravenous infusion: For example,; fluids infused intravenously
in dehydration.
• Advantages
1- Bioavailability is 100%.
2- Quick onset of action; therefore, it is the route of choice in
emergency, e.g. intravenous diazepam to control convulsions in
status epilepticus.
3- Large volume of fluid can be administered,
4- Highly irritant drugs, e.g. anticancer drugs can be given
because they get diluted in blood.
5- Hypertonic solution can be infused by intravenous route, e.g.
20% mannitol in cerebral oedema.
6- By i.v. infusion, a constant plasma level of the drug can be
maintained, e.g. dopamine infusion in cardiogenic shock.
• Disadvantages of IV
- Once the drug is injected, its action cannot be halted.
- Local irritation may cause phlebitis.
- Self-medication is not possible.
- Strict aseptic conditions are needed.
- Extravasation of some drugs can cause injury, necrosis and
sloughing of tissues.
- Depot preparations cannot be given by i.v. route.
• Precautions of IV
- Drug should usually be injected slowly.
- Before injecting, make sure that the tip of the needle is in the
vein
II)Subcutaneous (S.C.) Route
• The drug is injected into the subcutaneous tissues of the thigh,
abdomen and arm, e.g. adrenaline, insulin, etc.

• Advantages of SC route
- Actions of the drugs are sustained and uniform.
- Drugs can be given in presence of vomiting and diarrhea.
- Drugs can be given to unconscious patients.
- First pass effect is avoided.
- Drugs that are not absorbed from G.I.T can be given.
- Self-administration is possible (e.g. insulin).
- Depot preparations can be inserted into the subcutaneous
tissue, e.g. norplant for contraception.
• Disadvantages of SC route
- Only non-irritant drugs can be given otherwise severe irritation,
pain and necrosis of subcutaneous tissues can occur.
- Absorption of the drugs is slow than I/M injection.
- Expensive.
- Danger of infection, if proper sterilization techniques are not
used.
- Large volumes of drug cannot be given
iii. INTRAMUSCULAR (i.m) ROUTE
• The drug is injected deep in the belly of a large skeletal muscle.
The muscles that are usually used are detoid, triceps, Gluteus,.
Maximus, rectus, femurs depending on the specie of animal.
• The muscle is less richly supplied with sensory nerves, hence
injecting a drug 1m is less painful.
• Absorption of drug from gluteal region is slow especially in
females due to high fat deposition.
• Deep intramuscular injections are given at upper outer quadrant
of buttock to prevent the injury to major nerves.
• Deep I/M injections are less painful than I/M injections on arm
due to high fat content.
• Intramuscular injections are given at an angle of 90 degrees.
• Advantages
- Rate of absorption is uniform.
- Rapid onset of action.
- Irritant substances can be given.
-Drugs can be given to unconscious patients.
- Accuracy of dosage is ensured.
- Useful in emergency situations.
- First pass effect is avoided.
- Drugs producing gastric irritation can be given.
- Drugs that are not absorbed from G.I.T can be given.
•Disadvantages
- Small quantities up to 10 ml of the drug can be given at a time.
- Local pain and abscess formation.
- Technical person is needed, self-administration is difficult.
- Expensive.
- Danger of infection, if proper sterilization techniques are not
used.
- Chances of nerve damage.
iv. INTRATHECAL ROUTE
• Drug is injected into the subarachnoid space (spinal
anaesthetics, e.g. lignocaine; antibiotics, e.g. amphotericin B,
etc.).
v. 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
vi. INTRAPERITONEAL ROUTE
• Indication: Colon and Ovarian
• Peritoneal space has much surface area; may not be reached
by IV chemo
• Catheters used: implanted port
• Chemotherapy agents used: Cisplatin, Taxol
• Advantages: less systemic side effects
• Disadvantages: infection, pain.
vii. INTRAPLEURAL
• Seeding of pleura
• Used as sclerosing agent to stop pleural effusions
• Injected by physician into chest tube and clamped. Patient
changes position 15 min for 1 hour
• Chemotherapy agents used: Bleomycin, Adriamycin, Talc slurry
• Side effects: severe pain
viii. TRANSDERMAL ROUTE
• The drug is administered in the form of a patch or ointment that
delivers the drug into the circulation for systemic effect.
• For example, scopolamine patch for sialorrhoea and motion
sickness, nitroglycerin patch/ointment for angina, oestrogen patch
for hormone replacement therapy (HRT).
 •••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.
i. 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, Vaginal and anal canal:
• 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.
• As a suppository (administration of the drug in a solid form into
the rectum), e.g. bisacodyl— for evacuation of bowels.
•Advantages - Used in children. - Little first pass effect. - Can be
given in vomiting. - Can be given in unconscious patient. - Higher
therapeutic concentrations of drug are achieved rapidly in rectum.
- For rapid evacuation of bowel, usually during gut sterilization
before any surgical or radiological procedure.
• Disadvantages - Inconvenient. - Drug absorption is slow and
erratic. - Irritation or inflammation of rectal mucosa can occur.
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 (for bronchial asthma
and chronic obstructive pulmonary disease). Gases, volatile
liquids and solids (in the form of finely divided powders) are
inhaled for systemic and local effects. Inhalation of solids is called
insufflation. • Advantages - Rapid absorption of the drug due to
large surface area. - First pass effect is avoided. - Rapid local
effects. • Disadvantages - Only few drugs can be administered. -
May produce irritation of pulmonary mucosa. - Inconvenient
procedure. - Chances of cardiotoxicity.
f) Skin: As ointment, cream, lotion or powder, e.g. clotrimazole
(antifungal) for cutaneous candidiasis.
g) Transdermal: Transdermal patches can provide prolonged or
controlled (iontophoresis) drug delivery. Systemic absorption
(Transdermal) is better with low dose, low MWt, lipid soluble drugs
ii. 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.
iii. Administration of the drug into some deep tissues by
injection, e.g. administration of triamcinolone directly into the joint
space in rheumatoid arthritis.