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Routes of Drug Administration

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The “Right” ways of administering drugs

1. Right patient2. Right drug3. Right dose4. Right route5. Right time6. Right documentation

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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.

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How do we choose the right route of administration

• The route of administration is determined primarily by the properties of the drug (such as water or lipid solubility, ionization, etc.) and by the therapeutic objectives

• (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.

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Routes• Enteral/paraentral • Oral • Buccal• Rectal • Sublingual• Topical• Transdermal• Inhalant• Ophthalmic• Intranasal

• Otic• Vaginal• Intradermal• Subcutaneous• Intramuscular• Intravenous• Intraosseous• Intrathecal

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Enteral routes

• Drug placed directly in the GI tract:

– Oral - swallowing– Sublingual- placed under the tongue– Buccal route– Rectum- absorption through the rectum

(suppositories, anemas)– GI tubes (e.g. nasogastric, gastrotomy)

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Oral Route

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Oral Route

• 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.

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• Drugs are absorbed by:• Passive Diffusion: oDetermined by the lipophilcity of the drug

compoundo 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:oBy carrier proteins oExample: ca+2 is carried by V.t-D dependent

carrier system

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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 (~1-3 m2).

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?3. Food may delays gastric emptying time so that drugs

may destroyed by acid.4. Interactions between drug and food particles.

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Factors affecting GI absorption1- Altered gastric motility e.g. diarrhea2- Splanchnic blood flow (it decreases in shock)3- Particle size and formulation4- Physiochemical Factors: i.e. ions that affect

the absorption of some drugs. e.g. Tetracycline: it binds to ca and ca containing food

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Advantages of Oral Route

Advantages:– Convenient– 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

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Disadvantages:– Some drugs have an Unpleasant taste– Irritation to gastric mucosa can cause nausea and

vomiting– Destruction of drugs by gastric acid and digestive juices– 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

GI surgery– First-pass effect

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Systemic CirculationPortal Circulation

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First Pass Effect• When a drug is absorbed across the GI tract, it enters

the portal circulation before entering the systemic circulation.

• 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.

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• The greater the first-pass effect, the less the agent will reach the systemic circulation when the agent is administered orally.

• Lidocaine (anesthetic agent) is a drug with a first-pass effect that is so great that oral administration is not practical.

• Propranolol: significant portion of the orally administered dose is metabolized through a first-pass effect.

• 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.

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The oral route should generally be used when possible,

considering the patient’s condition and ability to take or

tolerate oral drugs

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Sublingual Route

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• The drug is placed in between gum and inner lining of the check

• Delivery of insulin to the buccal mucosa utilizing the RapidMist ™ system

Buccal Route

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Advantages• Rapid absorption• Drug stability• Avoid first-pass effect• Glyceryl trinitrate

Disadvantages• Inconvenient• Small doses• Unpleasant taste of

some drugs

Sublingual and Buccal Routes

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Rectal route

• 50% of the drainage of the rectal region bypasses the portal circulation; thus the biotransformation of drugs by the liver is minimized.

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Advantages of Rectal Route• Devoid of destruction of the drug by intestinal

enzymes or by low pH in the stomach• Unconscious patients (postoperative)• Children• If patient is nauseous or vomiting• Good for drugs affecting the bowel such as laxatives• Irritating drugs contraindicated• Can be used for both local effects and systemic

effects• Absorption may vary

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GI Tubes (e.g. nasogastric, gastrostomy)

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Liquid preparations are preferred over crushed tablets and emptied capsules, when available

Tube should be rinsed before and after instilling medication

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GI tubes

Advantages

Allows use of GI tract in patients who cannot take oral drugs

Can be used over long periods of time, if necessary

May avoid or decrease injections

Disadvantages

With nasogastric tubes, medications may be aspirated into the lungs

Small bore tubes often become clogged

Requires special precautions to give correctly and avoid complications

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Parenteral Routes

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• 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

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• Intravascular: Intravenous, Intra-arterial• Intraosseous (infusion - bone marrow drains

directly into the venous system.)• Intramuscular• Subcutaneous• Intracerebral (into the brain parenchyma)• Intra-cerebro-ventricular (in the cerebral

ventricular system)• Intracthecal (an injection into the spinal canal)

e.g. anesthesia, methotrexate

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Int rathecal in jection (subaracnoid space)

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Intra-articular

Femur(hip bone)

Joint capsule

Synovium

Corticosteroids are injected into the joint cavity to relieve pain and inflammation

Pelvic boneSynovial cavity (containing

synovial fluid)

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Tibia

INTRAOSSEOUS

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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.

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Intravenous (IV) • Injection is the most common parenteral route. For

drugs that are not absorbed orally, there is often no other choice.

Benefits• Rapid onset of action because the drug is injected

directly into the bloodstream• Useful in emergencies and in patients that are

unconscious• 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

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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 charcoal

• Risk of embolism (obstruction of blood vessel)• May introduce bacteria through contamination• Pain at application site• No self administration facility

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AdvantagesExtremely rapid action

Bypasses barriers to absorption

Drug levels are more accurately controlled

Good for administering irritant drugs

Suitable for large volumes

Can be administered to conscious / unconscious patients

Disadvantages

• Most dangerous route• Phlebitis commonly occurs and

increases risk of thrombosis.• Phlebitis / thrombosis may take

many days to subside• Must be performed slowly • Once injected, drug cannot be

removed• It may be difficult to find a

suitable vein. • Requires trained personnel .• Expensive - Sterility, pyrogen

testing and larger volume of solvent means greater cost for preparation, transport and storage

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Intra-arterial

• 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

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Intramuscular

• Drugs administered intramuscularly can be aqueous solutions or specialized depot preparations

• It is often a suspension of drug in a non-aqueous vehicle, such as ethylene glycol or peanut oil.

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Intramuscular AdministrationDorsal Gluteal

• Locate the posterior iliac spine.

• Locate the greater trochanter.

• Draw an imaginary line between these two landmarks.Injection site is above and lateral to the line.

• Most dangerous site because of sciatic nerve location

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Intramuscular AdministrationVentral Gluteal

• Palm of hand on greater trochanter of femur.

• Index finger on anterior superior iliac spine (hip bone).

• Middle finger extended.

• Injection site lies within the triangle formed by the index and middle fingers

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Subcutaneous• Drug is injected beneath the skin and permeates capillary

walls to enter blood stream.• Absorption from the site of injection is dependent on local

blood flow• 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.

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Subcutaneous Administration

Adapted from Smith, S.F., Duell, D.J., Martin, B.C. (2004) Clinical Nursing Skills Basic to Advanced, 6th Ed. Pg. 556. New Jersey: Prentice Hall

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INTRADERMAL SITES

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Inhalational• 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.

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Topical

• Topical application is used when a local effect of the drug is desired.

• Used for most dermatologic and ophthalmologic preparations.

• 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 errors.

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Transdermal

• 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, nitroglycerin.

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• 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)

Route for administration -Time until effect-