Route of Drug Administration

 

The technique in which drugs are administered, will to some extent affect their clinical advantage and whether patients practice some adverse effects, called Administration. The administration of drugs is a general process but a significant clinical process. It is the method in which the drug is administered that will regulate to some amount whether or not the patient advances any medical advantage, and whether they suffer any adverse effect from their drugs.

Most drugs can be administered by different routes. The choice of a suitable route in a given condition depends both on the drug as well as patient associated issues.

Routes can be broadly divided into two categories i.e. local route and systemic route, each of which has advantages and disadvantages.

1.      Local routes

These routes can be used for local injuries at nearby sites and for drugs whose systemic absorption from these sites is nominal or absent. Accordingly, high concentrations are achieved at the wanted site without revealing the remaining body. In this route, systemic side effects or toxicity are subsequently absent or insignificant. Generally, the local routes are: -

a.      Topical: This mentions to external application of the drug to the superficial for localized action. It is frequently more expedient as well as comforting to the patient. Drugs can be proficiently distributed to the localized injuries on the skin, nasal mucosa, eyes, ear etc.

b.      Arterial supply: This denotes the administration of a drug into the artery. The close intra-arterial injection is used for distinction media in angiography. Anticancer drugs can be instilled in the femoral artery to limit the influence for limb malignancies.

c.       Deeper tissues: Definite deep spaces can be loomed by using a syringe and needle, but the drug should be prepared in such a form that systemic absorption is slow. e.g. intra-articular injection (It is usually accomplished by joint injection symptomatic relief in osteoarthritis).

2.      Systemic routes

The drug administered by systemic routes is anticipated to be absorbed into the bloodstream and dispersed all over, comprising the site of action, through circulation. The systemic routes are: -

a.      Oral route

This is the most regularly used route of drug administration and is the most expedient and financial. Solid dose forms such as tablets have high drug stability and deliver precise dosage. The oral route is the ancient and commonest route of drug administration. It is nonviolent, more appropriate, does not need help, non-invasive, often trouble-free. When a drug is taken by oral route, food and other drugs in the digestive tract may affect the absorption of the drug. So, some drugs should be taken with food or should be taken on an empty stomach, some drug should not be taken with other drugs, and still, some drug cannot be taken orally at all.

Limitation of oral route:

·         The action of drugs is slower in this route so this is not suitable for critical cases.

·         Administration by this route may cause nausea and vomiting.

·         This route is not preferable for uncooperative/unconscious or vomiting patient.

·         The absorption of the drug by this route is very slow.

b.      Sublingual route (SL) or buccal route

The tablet or pellet comprising the drug is positioned under the tongue or crushed in the mouth and spread over the buccal cavity. Only lipid-soluble and non-irritating drugs can be so managed. The sublingual mucosa proposes a rich source of blood vessels by which drugs can be absorbed. This is not a general route of administration but drug absorption into the systemic circulation is rapid by this route. The main benefit is that the liver is bypassed and drugs with the first-pass metabolism can be absorbed into the systemic circulation.

c.       Rectal route:

Some irritant and disagreeable drugs can be put into the rectum as suppositories for systemic effect. This route can also be employed when the patient is having regular vomiting or is insentient. The rectal route has extensive drawbacks in terms of patient suitability and random drug absorption but it does offer several welfares.

d.      Cutaneous:

Very lipid-soluble drugs can be applied over the skin for sluggish and extended absorption. The liver is also avoided. The drug can be combined in an ointment form and applied over a quantified area of skin. The absorption of the drug can be improved by rubbing the drug ointment.

e.       Inhalation:

Volatile liquids and gases are administered by inhalation route for complete action, e.g. general anaesthesia. Absorption takings place from the infinite surface of alveoli- action is very quick. When administration is obsolete the drug disperses back and is speedily removed in expired air.

f.        Nasal:

The nasal membrane can voluntarily absorb many drugs such as digestive juices and liver are avoided. Though, certain drugs like GnRH agonists, calcitonin are used as a spray or nebulized solution have been used by this route.

g.      Parenteral:

Parenteral states to the administration of drugs by injection that takes the drug unswervingly into the systemic circulation or tissue fluid avoiding the skin and mucous membranes and deprived of having to cross the enteral mucosa.

Advantage:

·         Drug action is earlier and assured in this route.

·         Gastric irritation and vomiting are not provoked.

·         These routes can be working even in insentient, unhelpful or vomiting patient.

·         Patient compliance difficulties are mostly evaded.

Disadvantage:

·         Preparation has to be decontaminated and is expensive.

·         Invasive and painful.

·         The assistance of another person is mostly needed.

·         Probabilities of local tissue damage.

The important parenteral routes are: -

i.          Subcutaneous route (S.C.)

For this route, a needle is injected into the fatty tissue just below the skin. After a drug is inserted, it then transfers into small blood vessels and is passed away through circulation. Absorption of this route is slower than intramuscular (I.M.) injection. By this route, only small volumes of drug can be inserted. Self-injection is probable due to deep dispersion is not required.

ii.          Intramuscular (I.M.)

The drug is inserted in one of the enormous skeletal muscles such as the deltoid, triceps, gluteus Maximus, rectus femoris etc. This route is chosen before the s.c. route when greater volumes of a drug are required. Due to the muscles present beneath the skin and fatty tissues, a lengthier needle is used for injection. It is less painful, but self-injection is frequently unviable because deep dispersion is required. This type of injection should be evaded in anticoagulant treated patients because it can cause a local haematoma.

iii.          Intravenous (I.V.)

For this route, a needle is introduced directly into a vein. A solution comprising the drug may be administered in a single dose or by unremitting infusion. For infusion, the solution is moved by gravity. An i.v. injection is more challenging to administer as compared to an s.c. or i.m. injection because inserting a needle into a vein may be problematic, especially when the person is overweight or obese. Through this route, the drug spreads directly into the blood circulation and effects are produced promptly. The amount of the drug required is the least due to its bioavailability (100%).

iv.          Intradermal injection (I.D.)

The drug is inserted into the skin rising a bleb or scarring/multiple perforations of the skin by a drop of the drug are done. This route is used for precise purposes only.

 

References

1.      https://www.merckmanuals.com/home/drugs/administration-and-kinetics-of-rugs/drug-administration

2.     Tripathi, K. D. (2018). Essentials of medical pharmacology (8th ed.). Jaypee Brothers Medical.