Routes of Drug Administration
The “Right” ways of administering
Significance of Drug Administration
• Input of drug in the Human body.
• Permits entry of the therapeutic agent either
Directly or Indirectly into the Plasma.
• A drug once taken in any form has to be
then distributed, metabolized and finally
eliminated from the body.
How do we choose the right route of
• The route of administration is determined
primarily by the properties of the drug (such as
water or lipid solubility, ionization, etc.) and by the
• (for example, the desirability of a rapid onset of
action or the need for long-term administration or
restriction to a local site).
• The route of administration (ROA) that is chosen
may have a profound effect upon the speed and
efficiency with which the drug acts.
• Drug placed directly in the GI tract:
– Oral - swallowing
– Sublingual- placed under the tongue
– Buccal route
– Rectum- absorption through the rectum
– GI tubes (e.g. nasogastric, gastrotomy)
• Giving a drug by mouth is the most common
route of administration but it is also the
most variable , and requires the most
complicated pathway to the tissues.
• Little absorption occurs until the drug enters
the small intestine.
• Drugs are absorbed by:
• Passive Diffusion:
o Determined by the lipophilcity of the drug
o Ionized drugs are poorly absorbed (Strong
bases of pKa 10 or higher are poorly
absorbed, as are strong acids of pKa less
than 3, because they are fully ionized)
• Active Diffusion:
o By carrier proteins
o Example: ca+2 is carried by V.t-D dependent
Why most of the drugs are absorbed
from the small intestine?
1. Small intestine has a much larger surface area
for absorption (~200 m2) as compared to the stomach
2. Drug spends more time in the small intestine (~4 hrs)
than the stomach (~0.5-1 hrs).
Can food in stomach decrease absorption of drugs?
1. Food may delays gastric emptying time so that drugs
may destroyed by acid.
2. Interactions between drug and food particles.
Factors affecting GI absorption
1- Altered gastric motility e.g. diarrhea
2- Splanchnic blood flow (it decreases in shock)
3- Particle size and formulation
4- Physiochemical Factors: i.e. ions that affect
the absorption of some drugs. e.g.
Tetracycline: it binds to ca and ca containing
Advantages of Oral Route
– can be self-administered
– pain free
– Easy to take
– It is safe
– Absorption takes place along the whole length of
the GI tract
– Cheap compared to most other parenteral routes
– Some drugs have an Unpleasant taste
– Irritation to gastric mucosa can cause nausea and
– Destruction of drugs by gastric acid and
– Absorption is sometimes inefficient, only part of the
drug may be absorbed
– Effect too slow for emergencies
– Unable to use in unconscious patient or who have had
– First-pass effect
First Pass Effect
• When a drug is absorbed across the GI tract, it enters
the portal circulation before entering the systemic
• A drug can be metabolized in the gut wall or even in
the portal blood, but most commonly it is the
liver that is responsible for metabolism before the
drug reaches the systemic circulation (plasma). In
addition, the liver can excrete the drug into the bile.
• Any of these sites can contribute to this reduction in
bioavailability , and the overall process is known as
first-pass effect or first-pass elimination.
• The greater the first-pass effect, the less the agent will
reach the systemic circulation when the agent is
• Lidocaine (anesthetic agent) is a drug with a first-pass
effect that is so great that oral administration is not
• Propranolol: significant portion of the orally
administered dose is metabolized through a first-pass
• Nitroglycerin: More than 90% of nitroglycerin is
cleared during a single passage through the liver.
• Therefore, a much larger oral dose is required to
achieve the same therapeutic response as that
obtained from a dose administered intravenously. 16
The oral route should generally
be used when possible,
considering the patient’s
condition and ability to take or
tolerate oral drugs
• The drug is placed in
between gum and inner
lining of the check
• Delivery of insulin to the
buccal mucosa utilizing the
RapidMist ™ system
Sublingual and Buccal Routes
• Rapid absorption
• Drug stability
• Avoid first-pass effect
• Glyceryl trinitrate
• Small doses
• Unpleasant taste of
• 50% of the drainage
of the rectal region
bypasses the portal
circulation; thus the
drugs by the liver is
Advantages of Rectal Route
• Devoid of destruction of the drug by intestinal
enzymes or by low pH in the stomach
• Unconscious patients (postoperative)
• If patient is nauseous or vomiting
• Good for drugs affecting the bowel such as
• Irritating drugs contraindicated
• Can be used for both local effects and systemic
• Absorption may vary
GI Tubes (e.g. nasogastric, gastrostomy)
Liquid preparations are preferred over
crushed tablets and emptied capsules,
Tube should be rinsed before and
after instilling medication
• Parenteral administration is used for drugs
that are poorly absorbed from the
gastrointestinal tract, and for agents such
as insulin that are unstable in the GI tract
• Parenteral administration is also used for
treatment of unconscious patients and
under circumstances that require a rapid
onset of action
• Intravascular: Intravenous, Intra-arterial
• Intraosseous (infusion - bone marrow drains
directly into the venous system.)
• Intracerebral (into the brain parenchyma)
• Intra-cerebro-ventricular (in the cerebral
• Intracthecal (an injection into the spinal canal)
e.g. anesthesia, methotrexate
injected into the joint
cavity to relieve pain and
Intraosseous infusion is used commonly when there is failure to locate a suitable
veinous site, particularly in babies. This procedure is generally performed in the
Emergency Department or the Intensive Care Unit by a qualified practitioner.
• Injection is the most common parenteral route. For
drugs that are not absorbed orally, there is often no
• Rapid onset of action because the drug is injected
directly into the bloodstream
• Useful in emergencies and in patients that are
• The drug avoids the GI tract and first-pass metabolism
by the liver
• Smaller doses generally are required than the
other routes but cost is high
Disadvantages of Intravenous Route
Greater risk of adverse effects as:
• High concentration attained rapidly
• The amount injected cannot be recalled by
strategies such as emesis or binding to activated
• Risk of embolism (obstruction of blood vessel)
• May introduce bacteria through contamination
• Pain at application site
• No self administration facility
• Similar properties, advantages and
disadvantages of intravenous route.
• Intra-artery route is specially used when
high drug concentration in specific
tissue is required: Diagnostic purpose
and for chemotherapy
• Drugs administered intramuscularly can be
aqueous solutions or specialized depot
• It is often a suspension of drug in a nonaqueous vehicle, such as ethylene glycol or
• Locate the posterior
• Locate the greater
• Draw an imaginary
line between these
Injection site is above
and lateral to the
• Most dangerous site
because of sciatic
• Palm of hand on greater
• Index finger on anterior
superior iliac spine (hip
• Middle finger extended.
• Injection site lies within
the triangle formed by the
index and middle fingers40
• Drug is injected beneath the skin and permeates capillary
walls to enter blood stream.
• Absorption from the site of injection is dependent on local
• Concurrent administration of vasoconstrictor will slow
absorption. Epinephrine acts as a local vasoconstrictor and
decreases removal of a drug, such as lidocaine (local
anesthetic), from the site of administration.
• Examples of drugs given by this route are Insulin and
sodium heparin, neither of which is absorbed orally, and
both of which should be absorbed slowly over many hours.
Adapted from Smith, S.F., Duell, D.J., Martin, B.C. (2004) Clinical
Nursing Skills Basic to Advanced, 6th Ed. Pg. 556. New Jersey:
• Inhalation provides the rapid delivery of a drug across the
large surface area of the mucous membranes of the
respiratory tract and pulmonary epithelium, producing an
effect almost as rapidly as by intravenous injection.
• This route of administration is used for drugs that are gases
and volatile agents (for example, some anesthetics), or
those that can be dispersed in an aerosol.
• The route is particularly effective and convenient
for patients with respiratory complaints (for example,
asthma or chronic obstructive pulmonary disease) as drug
is delivered directly to the site of action and systemic side
effects are minimized.
• Topical application is used when a local effect of
the drug is desired.
• Used for most dermatologic and ophthalmologic
• Clotrimazole is applied as a cream to the skin in
the treatment of dermatophytosis.
• Atropine is instilled directly into the eye to dilate
the pupil and permit measurement of refractive
• This route of administration achieves systemic
effects by application of drugs to the skin,
usually via a transdermal patch.
• The rate of absorption can vary markedly
depending upon the physical characteristics of
the skin at the site of application.
• Small lipid soluble molecule.
• This route is most often used for the sustained
delivery of drugs, such as the antianginal drug,
Route for administration
-Time until effect-
intravenous 30-60 seconds
intraosseous 30-60 seconds
endotracheal 2-3 minutes
inhalation 2-3 minutes
sublingual 3-5 minutes
intramuscular 10-20 minutes
subcutaneous 15-30 minutes
rectal 5-30 minutes
ingestion 30-90 minutes
transdermal (topical) variable (mins to hrs)