By

Dr. Muhammad Adil RasheedAssistant Professor

Pharmacology and Toxicology

UVAS, Lahore

ROUTES OF DRUG ADMINISTRATION

Drug Absorption

Absorption is the process by which a drug enters the bloodstream without being chemically altered

or The movement of a drug from its site

of application into the blood or lymphatic system

Factors affecting route of drug administration

Physicochemical properties of the drug

Onset of action required Type of response required Site of desired action Nature and Formulation of drug Circulation at the site of absorption Biotransformation Condition of patient

The possible routes for drug entry into the body may be divided into two classes:

ENTERAL

PARENTERAL

Routes of Drug Administration

ENTERAL ROUTES

ENTERAL Drug placed directly in the GI tract:

Oral swallowing (p.o., per os)Sublingual placed under the tongueRectum Absorption through the

rectum

Oral Administration of drug by ingestion. Not very much preferred in animals because of

restraining of animals is difficult.

Given in the form of drench or mixed with feed or water.

Applied with the help of stomach tube, or Nasogastric tube.

If rapid effect is required drug may be administered before meal if drug causes irritation may be administered after meal.

Advantages of oral route Can be self- administered, pain free, easy to

take. Absorption takes place along the whole length

of the GI tract. The drugs preparations needs no sterilization. Both solid and liquid dosage forms can be

given through this route. Most suitable route for GIT Infections and GI

parasites Cheap as compared to most other parenteral

routes.

Disadvantages of oral route

Drug action has slower onset son not suitable in case of emergency.

Drug absorption is irregular and unpredictable due to presence of ingesta.

First-pass effect - drugs absorbed orally are initially transported to the liver via the portal vein.

Irritation to gastric mucosa - nausea and vomiting.

First-pass Effect The first-pass effect is the term used for the

hepatic metabolism of a pharmacological agent when it is absorbed from the gut and delivered to the liver via the portal circulation. The greater the first-pass effect, the less the agent will reach the systemic circulation when the agent is administered orally

Disadvantages of oral route

Destruction of drugs by gastric acid and digestive juices.

Unpleasant taste of some drugs.

Unable to use in unconscious patient.

Poor administration techniques may lead to intratracheal delivery and subsequent aspiratory bronchopneumonia

Sublingual/Buccal

Drugs are taken as solutions or smaller tablets which are held in the mouth or under the tongue.

Advantages Rapid absorptionDrug stabilityAvoid first-pass effect

Disadvantages Inconvenient Small doses Unpleasant taste of drugs

1. Unconscious patients and children. 2. If patient is nauseous or vomiting. 3. Easy to terminate exposure. 4. Absorption may be variable. 5. Good for drugs affecting the bowel such as laxatives.

Rectal route of drug administration

Parenteral Intravascular Intravenous Intra-arterial

Extravascular Intramuscular Subcutaneous Intra-articular Intraperitoneal Intracardial Intrapleural Epidural Intradermal Intrathecal Intraoosseous

Other Extravascular Inhalation Topical Application Other Mucous Membranes (Vagina, Nose…)

Intravascular

Intravenous Intra-arterial Absorption phase is bypassed (100% bioavailability)1.Precise, accurate and almost immediate onset of action, 2. Large quantities can be given, fairly pain free3. Greater risk of adverse effects a. high concentration attained rapidly b. risk of embolism

Intravenous route of drug administration

Drug solution is injected directly in one of superficial vein either as bolus or infusion.

In cattle and Horses vein is jugular, In sheep and goat jugular, Caphaneous and cephalic, vein is and in dog vein is Caphaneous and cephalic.

Identify the vein to be used  in some animals this is straightforward, others may have to palpate (feel for) veins. Always inject with the blood flow.

Clean the site  with soap and water, or an alcohol swab.

Introduce the needle into the vein at a shallow angle.

Pull back the plunger to identify that the needle is in a vein  a small amount of dark red venous blood should trickle into the syringe.

Inject slowly to reduce the likelihood of damage to the vein and to lower the overdose risk.

Remove the needle slowly  if the needle is removed too quickly, the vein may collapse.

Immediately apply pressure to the site  bruising is caused by bleeding into the surrounding tissues. Immediate firm pressure will limit the amount of bruising caused.

Intravenous route of administration

Advantages of Intravenous route

Quick onset of action.

This route is used when precise control of the drug effect is required.

Highly irritating and non isotonic solutions can be given by slow IV because dilution provided by circulating blood.

Large volume of fluids can be administered through this route.

Disadvantages of Intravenous route

This route required special technique.

Air embolism may put life of animal in danger.

Extra vascular accumulation of irritant drugs may cause necrosis of peripheral tissues and phlebitis.

Not suitable for insoluble drugs like oils and suspensions.

Intramuscular route of administration

Drug is injected deep between the layers of one of large skeletal muscle because these are richly supplied with blood and less with nerves.

This route is used for providing systemic effects of drugs.

Advantages of Intramuscular route

Route of choice in animals.

Very rapid absorption of drugs in aqueous solution and oleaginous suspensions.

Absorption of drug is rapid except for oily and depot preparations.

The duration of action is longer than for IV injection, but usually a little shorter than for subcutaneous administration.

Mostly suitable route for fractious, wild and zoo animals, which may be difficult to restraint.

Large volume of fluids cannot be injected.

There is possibility of improper deposition of drug in nerve, blood vessels, fat or connective tissues.

It is not suitable for emergency situations because conditions like cardiovascular collapse or shock may impede absorption of drugs.

Disadvantages of Intramuscular route

Subcutaneous route of administration

The drug preparation is deposited in the loose subcutaneous tissue (Under skin).It is richly supplied with nerve but less blood supply.

AdvantagesLarge volume of non irritating drugs may be administered.

Absorption of drugs is slower than IM and IV.

It is suitable for depot preparations.

DisadvantagesNot suitable for irritant drugs

Intradermal route of administration

The drug preparation is injected in the dermis of skin.

Injection is applied on the skin of most sensitive part of body.

Advantages

Used for diagnostic purposes, like tuberculin test, Malein test, Antibiotic sensitivity test.

Disadvantage

Painful condition.

Intra articular Injection

Inject the drug in Joints For the treatment of arthritis More skill is required Painful application

Damage the cartilage

Intraperitoneal drug administration Injection into Peritoneum  (body

cavity).

IP injection is more often applied to animals than humans.

It is generally preferred when large amounts of blood replacement fluids are needed, or when low blood pressure or other problems prevent the use of a suitable blood vessel for Intravenous Injection.

Advantages Rapid absorption Large volume of drug may be injected. Used frequently in lab animals.

Disadvantages Not suitable for irritating compounds because it

causes chemical peritonitis. There is possibility of puncturing of intestine or

other abdominal organs.

Intra Cardiac Injection

Drug is injected directly in to the heart

Epidural Injection

An injection in the epidural space. It is a space located in the spine between

the vertebrae and the dural sac, which surrounds the spinal cord.

Intrathecal Injection

Drugs which cannot cross BBB are administered through this route

Intraoosseous Injection

Injection in Bone marrow

1.Gaseous and volatile agents and aerosols 2.Rapid onset of action due to rapid access to circulation a. Large surface area b. Thin membranes separates alveoli from circulation c. High blood flow

Other Extravascular Inhalation

Topical route of drug administrationSKINAbsorption is directly proportional to the lipid solubility of drugs. Absorption through skin can be enhanced by use of dressing, inunctions or special drug delivery devices like ear tags and transdermal patches.BATHIt is immersion of the body in medicated water. Baths are given generally for their local effects upon the skin in cutaneous disorders.DIPSIt is type of bath in which body is dipped in medicated fluid for a certain time. In vet. Dips are used in small animals to kill ectoparasites.

Topical route of drug administration

INUNCTIONSIt is the application of semisolid or liquid drug on the body by rubbing.DUSTINGIt is application of fine particles of solid on surface of body.

APPLICATION ON MUCOUS MEMBRANESIntramammary Administration.Intra ocular Administration.Intra aural Administration.Intranasal Route.IntravaginalIntrauterineIntra Prepucial

Specialized drug delivery systemsTransdermal Drug delivery systemTransdermal drug delivery system are topically administered medicaments in the form of patches that deliver drugs for systemic effects at a predetermined and controlled rate.

Liposomes.Liposomes are minute vesicles of lipid bilayers enclosing and aqueous compartment. They are utilized for the transportation of drugs to areas not normally accessible to free form of drug.

Specialized drug delivery systems

Dermojet/HyposprayIt is a special form of subcutaneous administration in which needle is not used. A high velocity jet of drug solution is projected from a micro fine orifice using a gun like device. It is painless method for insertion of drug in the body.

Specialized drug delivery systems

Intravenous 30-60 seconds Intraosseous 30-60 seconds 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 (minutes to

hours)

Route for administration -Time until effect-

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