Routes of Drug Administration

Routes of Drug Administration: In today’s world of medicine, drugs are available in varied forms. Some are liquids, some are biphasic liquids while certain preparations are semisolids. The tablets, capsules, suspensions, ointments, injections, sustained-release preparations are some of the types of pharmaceuticals used in practice today. Hence, administration of these preparations also differs from type to type. Some are given orally while others are to be applied externally or to be injected into various body tissues. In this article, we will deal with the different routes of administration of drugs and the advantages and disadvantages of each route.

Systemic Effect :

The effect produced by the drug after being effectively absorbed in blood stream is known as systemic effect.

Local Effect :

The effect produced by the drug in a localized area where it is applied (administered) is known as local effect.

For systemic effect of drug, the possible routes for drug entry in the body may be divided into two main classes, viz., Enteral and Parenteral. For local effect the drugs may be applied externally.

Routes of Drug Administration

ENTERAL ROUTE

The term enteral is derived from word Enteron meaning intestine. In this case, the drug is placed directly in the Gastrointestinal tract (GIT). Three types of enteral routes are known: the oral route where the drug is taken in the mouth cavity and swallowed, the sublingual route where the drug is kept under the tongue and the enema where the drug is administered in the rectum, through the anus.

(A) Oral Route of Administration :

In this route of administration, the drug whether liquid or solid preparation is placed in the mouth cavity and is swallowed along with drinks such as water, milk etc. Sometimes the tablet is chewed by the patient and is then swallowed from mouth cavity. After administration of drug by this route, absorption of drug takes place in the intestine.

Advantages :

(1) Oral route of administration is the most commonly preferred and used route for drug of administration. Most of the medicinal preparations are consumed orally.

(2) Drug administration by this route does not require any special skill is essential, the route is very convenient and economical from infants upto the aged patients.

(3) Drugs to be utilized by this route needs no complicated processes such as sterilization.

Disadvantages :

(1) Though the oral route is widely used in the medical field, it also has certain limitations for its use in some emergency cases.

(2) It cannot be used in cases of unconscious and in-cooperative patients.

(3) Patients showing symptoms of vomiting and diarrhea cannot consume drugs by oral route.

(4) Certain drug preparations such as insulin undergo degradation in the gastrointestinal tract. Hence, such preparations cannot be given by oral route in order to avoid their degradation by digestive juices.

(5) After oral administration certain drugs like testosterone are destroyed in the liver cells (Hepatic first pass metabolism).

(6) The onset of action of drugs administered by oral route is upto 3-4 hours. Due to delayed onset of action, oral route cannot be used for drug administration in clinical emergencies.

Technique of Administration :

As far as the oral route of administration is concerned no special technique of administration is required. The tablet or capsule must be simply placed in the mouth cavity and swallowed with water or any other suitable liquid. For liquid preparations,
they are just to be swallowed.

(B) Sublingual Route of Administration:

In this case, the tablet of medicament is to be placed below the tongue and is allowed to dissolve in the mouth cavity. Thus, the active medicament gets absorbed through the buccal mucous membrane. The absorbed material is then directly passed into the systemic circulation. Ephedrine Hydrochloride tablet is administered by this route for the treatment of asthma. The tablet of Nitroglycerine used as a treatment regieme for Angina Pectoris is also administered sublingually.

Advantages :

(1) As this route shows rapid onset of action, it is useful in medical emergency cases such as in Angina Pectoris.

(2) The adverse effects of the drug can be prevented simply by spitting the tablet. Also, the drug effect can be effectively terminated by spitting of the tablet.

(3) As the drug directly reaches the systemic circulation, degradation of drugs in the stomach is avoided.

(4) Inactivation of the drugs in the liver is also avoided as the drug bypasses the portal circulation before reaching the blood.

Disadvantages :

The only disadvantage of this route is that the drugs having direct or toxic effects on heart should be cautiously administered by taking utmost care to avoid any such effect.

(C) Enema or Enemata :

This route involves administration of a liquid medicament into the rectum. The enemata is of two types which are as follows :

(i) Evacuant Enema: It is employed to remove the faecal matter. It is also used to remove flatulance. The maximum quantity of fluid administered at a time is about 600 ml. e.g. soap water enema. The water administered stimulates the rectum by distension while soap lubricates the pathway. This type of enemata is utilized before surgical operations, delivery and investigation of gastrointestinal tract by
X-rays etc. As it evacuates the bowel it is termed as evacuant enema.

(ii) Retention Enema: Here the administered fluid contains a medicament which is retained in the rectum. Thus, the medicament acts locally as predinisolone enema in ulcerative colitis. Sometimes the drug may act systemically by absorption through mucous membrane, e.g., Paraldehyde enema for production of basal anaesthesia. In this case the quantity of fluid administered is about 100-120 ml.

PARENTERAL ROUTES OF DRUG ADMINISTRATION

The parenteral routes includes the routes of drug administration other than the alimentary tract (“enteron”). In Latin “par” means beyond and “enteron” means intestine. Thus, in case of parenteral routes a drug in the form of solution or suspension is either injected in the body with the help of a hollow needle and a syringe (injection) or in some cases in the form of vapour or fine droplets drugs are inhaled in the respiratory tract (Inhalation).

Advantages :

(1) Injections can be employed in an unconscious or an uncooperative patient.

(2) They are also useful for the patients suffering from vomiting or diarrhoea or who cannot swallow things.

(3) Irritation of stomach by the drugs is avoided.

(4) Drugs which does not get absorbed from the small intestine can also be administered.

(5) This route has rapid onset of action which is a plus point in case of medical emergencies.

(6) Injections ensure accurate dosage of the medicaments.

Disadvantages :

(1) As these routes require special techniques of administration, these are not very convenient and economical for the patient.

(2) It is very difficult to control or reverse the effects of drugs administered by these routes.

(3) Self-medication is difficult in this case as drug administration by this route requires special technical skill.

(4) It is essential to follow strict aseptic technique in order to avoid possibility of infections.

(5) Skilled person is necessary for the injections to avoid injury to nerves, blood vessels, etc.

(I) INJECTIONS

(a) Intradermal Injection :

In this case, the drug is injected in the layer of the skin. Only a small quantity of the drug can be administered by this route and the injection is painful. This route is used for detecting allergy to the drugs, e.g., Penicillin is injected intradermally to observe allergic reactions to it. Also, vaccines are administered generally by this route, e.g., B.C.G. vaccine, small pox vaccine.

(b) Intravenous Injection :

In this case, the drug is injected directly into the veins. By this route, the drug produces rapid action and desired blood concentration of the drug is obtained by a definite dose. This route is quite useful for administering irritant and hypertonic solutions. Drugs with oily vehicles or those precipitating blood constituents should not be given by this route. Drugs should not be injected into the blood stream unless it is specifically indicated to do so.

Advantages:

(1) The onset of action of drug is very rapid. Hence, this route is effective in emergency cases. The approximate time for onset of action is found to be fifteen seconds.

(2) Large quantities of drugs can be administered by this route. Hence, it is useful for administration of normal saline solution.

(3) The irritating as well as hypertonic solutions can be administered intravenously because the drug is immediately diluted by the blood
stream.

(4) The desired blood concentration of the drug can be obtained accurately and immediately which is not possible to achieve by any other route.

Disadvantages :

(1) Utmost care is to be taken to see that the needle is inserted in the vein and drug is not leaking out from the site of injection. If the drug leaks out, it causes abscess formation and irritation around the site of injection.

(2) Speed of drug entering into the vein must be cautiously controlled and maintained. In certain cases the speed should be slow for drugs like Iron and Aminophylline as high concentration of these drugs in blood may be dangerous.

(3) Once the drug is administered intravenously, there is no retreat and its side effects are also quicker than that of drug given by any other route.

(c) Intramuscular Injection :

In case of intramuscular route the drug is injected into the muscle tissues. Drugs administered by intramuscular route includes soluble substances, mild irritants, suspensions and colloids. The absorption is farely uniform and even rapid as compared to subcutaneous injection. The volume of injection should be upto 10 ml.

Advantages:

(1) Mild irritants, suspensions, colloids and injections with insoluble oily bases can be administered by this route.

(2) This route also ensures uniform and slow absorption of drugs which include drugs with low solubility as well as repository penicillin
preparations.

Disadvantages :

(1) If proper care is not taken, there is possibility of injury to the nerves.

(2) Injected drug may produce local pain and abscess formation.

(3) Total volume of drug injected is restricted upto 10 ml.

(4) Certain intramuscular injections need more time for absorption as compared to oral administration; e.g., Intramuscular Diazepam, Digoxin, Phenytoin.

(d) Subcutaneous Injection :

In case of subcutaneous route, drugs are injected below the skin. Only non-irritant substances can be injected by this route. There is a slow absorption of drugs in this route as compared to intravenous and intramuscular injections. Inspite of slow absorption, the drug action is well sustained and uniform e.g., Protamine zinc insulin. Adrenalin in oil, certain hormones etc.

Hypodermoclysis :

This is a special process of injecting large amount of drugs through the loose subcutaneous tissues of the body. The best sites for hypodermoclysis include thighs, buttocks etc. This method is particularly useful in conditions where vein puncturing is difficult, e.g., in pediatric practice normal saline solution is given by this route.

Hypospray :

This method involves the subcutaneous introduction of a drug by means of high velocity jets projected through a fine orifice. This method is devoide of needles and thus avoids pain during injection. It is particularly useful for mass innoculation programme. It is also termed as “jet injection”.

Implants :

The advantage of sustained and slow action of drugs produced by subcutaneous injection is utilized in sustained release preparations in the form of implants. These subcutaneous drug implants can act as “depot”, e.g., DOCA or testosterone implants. These implants may be effective substitutes for repeated injections which can last for a period of about 9 to 15 months.

(e) Intraarterial Injection :

In this type of injection, a drug is injected directly into the artery. This leads to localisation of drug effect in a particular organ or tissue. The anticancer (antineoplastic) agents are given by this route. This route is also used for diagnostic studies and for injection of some antimalignancy drugs. But, due to various risks this route is used rarely and by experts only. The drug inserted may produce a sudden
high concentration of drug in the arterial blood and hence may be harmful locally or prove fatal for the tissue.

(f) Intrathecal Injection :

This route involves introduction of drugs in the subarachnoid space. This route is used when local and rapid effects of drugs like spinal anaesthetics, antibiotics and corticosteroids on the meninges are desired. Besides, this is also useful in spinal anaesthesia and acute central nervous system infections. Intrathecal administration requires a strict aseptic technique.

(g) Intraperitoneal Injection :

In this route, the drugs are injected into peritoneal cavity which offers a large absorbing surface. The drugs so absorbed enter the circulation § rapidly. Intraperitoneal injection is commonly employed in laboratories and is used very rarely in the clinical practice. It is used to give fluids like glucose saline solution to infants. There is a vast danger of adhesion and infection in employing this route.

(h) Intramedullary Injection :

When intravenous administration is not possible, the drugs are directly injected into the bone marrow. Intramedullary injection has most rapid onset of action after intravenous injection. This route of administration is particularly employed in infants and in restless patients; when veins are either blocked or useless for circulation due to thrombosis or circulatory collapse. This route is contraindicated in patients with history of bacteremia and osteomyelitis. Drug is inserted in sternum in adults and in the tibia or femur in children. This route is used occasionally for administration of blood in infants. Intramedullary injection requires all the necessary precautions involved in intravenous injection.

(i) Intraarticular Injection :

Intraarticular injection involves administration of certain drugs directly into a joint. This route of drug administration is employed for the treatment of local conditions which can achieve’ high local concentration of the drug e.g., Hydrocortisone acetate is given by this route in the treatment of rheumatoid arthritis. As in previous cases, it also requires perfectly sterile drug for the injection to avoid any possibility of infection.

Technique of Administration :

Injectional route includes administration of drug either in solution, suspension or emulsion form into different body parts with the help of hollow syringe and needle. When the syringe is filled and pressed, the drug leaks out through the needle and enters the body tissues. But, this ‘shot’ is painful and needs surgical sterility and proper skill. Hence, only qualified persons are able to give injections.

(II) INHALATION

In case of inhalation route, drugs are administered either as aerosole systems, or in the form of vapours. Besides this, certain drugs can be sprayed in the form of minute droplets which gets deposit over the mucous membranes, thus producing local effects. The best example of this type is Adrenalin spray used in the treatment of bronchial asthma. The drugs can also be administered as gases or in the form of
smoke. These include carbon dioxide gas and other volatile general anaesthetics. Absorption by this route is rapid, easy and high local as well as systemic concentration of the drug can be achieved.

Advantages :

(1) Drugs given by this route can be absorbed very fast resulting in rapid local and systemic effects of the drugs.

(2) The systemic concentration of volatile substances such as anaesthetics can be effectively controlled.

Disadvantages :

(1) As the drugs directly enters the left side of the heart, there is a danger of cardiac toxicity.

(2) Certain drugs producing local irritation may increase respiratory tract secretions.

(3) A special technical skill and sometimes specially designed apparatus is essential for administration of the drugs.

Technique of Administration :

Special apparatus such as masks etc. are to be used for inhalation of general anesthetics. Sometimes aerosol systems with automizer are used for spraying suspensions.

Aerosols, the stable suspensions of very fine liquid or solid particles in a medium are produced and administered by nebulizers.

(III) LOCAL APPLICATIONS

These preparations are meant for their action at the site of application. These external preparations include dusting powders, pastes, lotions, drops, ointments and plaster. The well known example of external preparation for local application is posterior pituitory powder used as a snuff for the treatment of Diabetes insipidus. Occasionally, the drugs may be utilized for their systemic action i.e., by injection or applied by rubbing, e.g., cod liver oil. Sometimes drugs may be applied locally as bougies for urethra, pessories for vagina and suppositories for rectum.

Advantages:

(1) These preparations provide an easy route of administration of certain medicament.

(2) Local applications, in general, are useful when prolonged effect of a drug is desired.

(3) These preparations decrease the possibility of systemic absorption of medicaments.

Disadvantages :

(1) Drugs in the form of watery solutions are sometimes absorbed in the blood which may lead to an undesirable toxic effect when applied on mucous membranes.

(2) The drugs for corneal application may penetrate or effect the ciliary muscles e.g., cocaine.