Parenteral routes/ Injection

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Parenteral routes/ Injection:

It literally means routes other than gastrointestinal, but technically it refers to drug administration by injections under one or more layer of skin or mucous membrane.

Commonly used parenteral routes in veterinary medicine are:

a. Intravenous (I.V/IV) route:

Drug is injected directly into one of the superficial veins. Drugs immediately reaches systemic circulation and effects are produced rapidly.
Comparatively, small amounts of solutions is given by intravenous injection and large amount is administered through intravenous infusion.
Inserting needle is vein is difficult than any other routes because it requires special skill and proper restraining of animals.
Used for administering irritating solutions, rehydrating fluids, total parenteral nutrition and whole blood.

Advantages:

Produces quickest onset of action (15-30 sec) as drug is directly released in veins reaches heart immediately and distributed throughout the body rapidly.
It is most reliable route for acute situations, emergency medications and intensive care therapy due to rapid action and predictable plasma drug concentration.
It is best route to deliver precise dose quickly and in a well-controlled manner throughout the body.
It is only route by which highly irritating drugs and non-isotonic solutions can be given.
Large volume of fluids and large doses of drug can be administered without ill-effects by extending the time of infusion.

Disadvantages:

It requires trained personnel and special skills for careful injection.
It is most dangerous route of administration as it by-passes most body’s defense exposing the vital organs to high concentration drugs.
It requires the drug preparation to be perfectly sterile, pure and soluble presence of even traces of undissolved substances may lead to life-threatening infection, abscesses or allergic reactions.
It is not suitable for insoluble drugs, oily substances, or drugs in suspension. Drugs must be in aqueous solutions.
Poor injection technique or air embolism may put life of animal in danger.
Once injected, the drug cannot be removed.

b. Intramuscular route (I.M):

Drug is injected deep between the layers of one of large skeletal muscles. They are mostly carried out by hand injections or may also be carried out by darting.
Lipid-soluble drugs diffuse freely through capillary walls and are well absorbed when administered intramuscularly.
It is used for providing only systemic effects of drugs.
Used routinely for administration of many vaccines, antibiotics and steroids.

Advantages:

It can be used for solutions, aqueous solution and oleaginous suspension and other depot preparations.
It provides fairly rapid absorption of drug.
Mild to moderately irritant preparations can be injected.
It provides longer duration of drug action than IV injection but little shorter than SC administration.
It is mostly suitable for fractious, wild and zoo animals, which may be difficult to restraint.

Disadvantages:

Larger volume of fluids cannot be injected.
Improper injection technique may cause deposition of drugs in nerves, blood vessels, fat or connective tissue.
It is not suitable for emergency situations.
Repeated use of same site may leave the muscles sore and stiff.
Absorption is sometimes erratic, especially for poorly soluble drugs.

c. Subcutaneous route (S.C):

Drug preparation is deposited in the loose connective tissue just under the skin. The injected drug moves from the subcutaneous tissues into capillaries and then carried away by the bloodstream.
It is used for providing systemic effects of drugs. It is used for administering many protein drugs.

Advantages:

Relatively large volume of non-irritating drug may be administered.
Absorption of drugs is continuous but gradual and slower than from I.M sites.
It is suitable for pellet implantation and depot preparation.
Rate of drug absorption can be manipulated to some degree by use of a vasoconstrictor or cold or heat or massage to the injected site.

Disadvantages:

it is not suitable for irritant drugs as they may cause severe pain, tissue necrosis and sterile abscess formation.
It requires drug formulation to be strictly isotonic and at physiological pH.
It is not suitable in shock states because reduced peripheral circulation markedly hampers the absorption rate.

d. Intraperitoneal route:

Drug preparation is deposited into the peritoneal space. Peritoneum provides a larger surface area for absorption of drugs.

Advantages:

Disadvantages:

Not suitable for administering irritating compounds.
Not frequently used in large animals due to danger of infection and peritoneal adhesions.
Improper and faulty injection may lead to puncturing of intestine and other abdominal organs.

e. Epidural route:

Drug is deposited through vertebral interspace into epidural space.
In this route, needle donot puncture the meninges and there is less risk of traumatic injury to spinal cord.
It is commonly used in large animals to provide epidural anesthesia.

f. Intrathecal route:

Drug is injected into subarachnoid space.
Local anesthetics, analgesic and chemotherapeutic agents are given through this route.
Intra-arterial route:
Drug is injected directly into artery.
It produces high concentration of drugs in dependent area for short period of time, which is essential in cancer chemotherapy and in special radiographic or imaging techniques.
It may cause weakening of arterial wall or infection of arterial wall (aneurysm) which is life-threatening to patients.

g. Intra-medullary:

Drug is administered directly into the marrow of the bone.
Used mainly for blood transfusion or fluid therapy when other routes are not possible, especially in neonates.

h. Intradermal/intracutaneous route:

Drug is injected within layers of skin (dermis).
Provides localized effects and used mainly for testing hypersensitivity of drug or producing infiltration anesthesia.
Occasionally, used for vaccination purposes.

i. Intra-articular route:

Drug is administered directly into the joint space.
Used primarily to obtain high local concentration of drugs within inflamed joints.

j. Intracardiac route:

Drug is administered directly into the heart muscle.
Rarely used in emergency situations; as in cardiac arrest.
Epinephrine is used occasionally through this route during cardio-pulmonary resuscitation.

k. Intratracheal route:

Drug is administered in between the rings of trachea, especially in middle third of neck.
It is used primarily for treatment of respiratory tract infections.

l. Intracerebral route:

m. Other parenteral routes: