Parenteral administration is a route of drug administration devoid of oral route.
Here the drug is given from routes other than oral i.e. avoiding alimentary canal.
The name Parenteral come from “para”= aside + “enteral” = intestine.
Parenteral administration definition: It is a method of delivering the drug directly into the blood stream without having to pass the oral or alimentary mucous layer. I.e. the drug by passes the gut and enter the blood stream.
This route of administration is possible if the drug is in liquid dosage form.
This route is risky but has many advantages than the oral route of drug administration.
Parenteral administration types:
The administration is mostly done by using needle and is of following types
- Intra venous
1. Intavenous injection: This route delivers drug directly into the blood veins. The formulation is given as a single lump or slowly by drip over a period of hours.
In most cases, the superficial veins are selected for injection. It is route which shows fastest action compared to all others. This route is regularly used in times of emergency and critical care. Read more on what is IV therapy
2. Intramuscular: Here the drug is given directly into the large skeletal muscles.
The drug is released slowly from the sites of injection as the blood flows through. Since the muscle has less sensory nerves, irritant drugs can be given without pain. Also the drug formulation can be in suspension or oily form.
3. Intra-peritoneal: Administration of drugs into the peritoneal cavity is called intra-periotneal injection. This method is less used in humans but widely used in research animals used for drug testing. The injection is done at the abdominal region below the skin into peritoneal cavity.
4. Subcutaneous: Here drug is injected just below the skin. This route is used for vaccines, disease diagnosis etc. The drug is deposited into the loose subcutaneous tissue which has many nerves. So irritant drug must be avoided as it can be painful. The rate of drug absorption is slower than that from intramuscular injection. It is of different types like
a) Dermojet: Here a delivery system devoid of needle is used. It has very fine orifice and drug solution is projected by shot such that it reaches just below the subcutaneous tissue. The method is painless and suitable for mass inoculations.
b) Pellet implantation: Here a solid pellet containing drug is implanted subcutaneously. The drug is released slowly over a period of few months. Especially steroids like deoxycorticosterone, testoserone are given.
c) Subcutaneous injection: Here a syringe with fine needle is used to administer the drug in loose skin tissue. The injection can be very painful and used in cases like anti-rabies injection etc.
5. Intra-dermal injection: Here drug is given into the skin so it form a small bulge. Used for vaccincation and drug allergy testing.
6. Intrathecal: Here drug is administered into the spinal cord.
7. Epidural: The drug is injected near the spinal cord such that it affects the local nerves. Mostly used in anesthesia during surgery, delivery etc.
8. Intraosseous: The injection is done directly into the bone marrow. The needle has to pass through the solid bone and reach the marrow. This is route is possible in children as the large bones are not completely hardened and are a bit soft to allow the penetration of the needle.
Advantages of parenteral drug administration:
1. For emergency: When the drug has to start acting immediately in case of emergecy this is best. For example in case of heart failure, digoxin or adrenalin can be directly administered.
2. For unconscious patient: When patient is unconscious, he cannot swallow the medicine, then injection is best.
3. Avoid first pass metabolism: When a drug is taken by mouth, it has o pass the liver. Here most drugs undergo metabolism and may get destroyed before they show their effect. This is called first pass metabolism. For drugs which are destroyed by liver first pass metabolism, injection helps to avoid it.
4. Minimal wastage of drugs: When the drug is given by tablet form, it may not be completely absorbed from the gut and even some of it may be metabolized in the liver before it reaches blood. So more quantity of drug is required to produce desired effect. Here, the drug is directly released into blood stream by injection so minimum drug is needed to produce the effect as there is no wastage.
Disadvantages of parenteral administration:
1. Expensive method of drug administration: Inject able drugs are expensive as they need the instruments like syringe,
2. Needs a skilled help for injection:
3. Risky route: Drug once given cannot be controlled if there are adverse effects or poisoning. Where as if given by oral route, the chances of risk are reduced due to digestion or metabolism. Also drug absorption can be stopped by timely administration of charcoal. This is not possible in injection route. Hence we see anaphylactic shock on giving few drugs and it is difficult to control adverse effects leading to death.
4. Chances of pain and injury at site of injection.
5. Effective sterilization is required. The formulation and syringe needs sterilization else can lead to infections. Hence we see transmission of HIV-AIDS through contaminated needles.