ROUTE OF DRUG ADMINISTRATION

“Route of drug administration is the path through which a drug or any substance enters into body or body fluid circulation”.

The following factors decide the route of drug administration:

1. Drug characteristics and their properties

2. Therapeutic objective

3. Routine treatment or emergency treatment

4. Site of action: Local or Systemic

5. Patient age

6. Patient condition

7. Patient preference

8. Doctor choice

The route of drug administration can be divided into the following types:

1.  Local Route of Drug Administration

2. Systemic Route of Drug Administration

LOCAL (Topical) ROUTE OF DRUG ADMINISTRATION

The drug is applied directly to the site of action, usually on the skin or mucous membrane. Common topical forms include creams, lotions, ointments, and foams.

The following sites are used for the local application of the drug:

1. Skin: Ointment, Lotion, Cream, Powder, Transdermal Patches

2. Eye, Ear, and Nose: Eye drops, ointment, spray

3. Oral cavity: Suspension, ointment, jelly, spray.

4. Bronchi: Inhalation, gases, volatile liquid, volatile solid (insufflations)

5. Gastrointestinal tract: Antacid, GIT sterilisation before surgery

6. Rectum: Enema, Suppository.

7. Vagina: Enema, Suppository, Douches

8. Urethra: Bougie, Pessary

9. Anal canal: Enema, Suppository.

   1. a. Enema: Drug is administered in liquid form. It may be an evacuated enema (similar to a saline enema) or a retention enema in the treatment of ulcerative colitis.

   2. b. Suppository: Drug is administered in solid form.

10. Artery: The drug is injected directly into an artery to deliver it to diseased cells. It is used in disease diagnosis (e.g., coronary angiography) and for administering anticancer drugs to cancerous tissues. This route is rarely used.

11. Deep tissue: The Drug is administered into deep tissue by injection. Ex: Administration of a drug directly into joints to treat Rheumatoid Arthritis.

Advantages

1. Produces direct action at the site of application.

2. Fewer systemic side effects as absorption is minimal.

3. Rapid onset of action at the target site.

4. Avoids first-pass metabolism.

5. Requires a smaller dose of the drug.

Disadvantages

1. It can be used only on accessible areas of the body.

2. Poor absorption through the skin or mucous membranes for some drugs.

3. Short duration of action,

4. It needs frequent application.

5. May cause local irritation or allergy.

6. Not suitable for systemic effects.

LOCAL ROUTE OF DRUG ADMINISTRATION

A. Rectal, Vaginal, and Urethral Routes:

Advantages:

• 1. Useful in unconscious patients

• 2. Useful in vomiting conditions

• 3. Useful in children

• 4. No first-pass metabolism of the drug

• 5. Higher drug concentration at the site of action

• 6. Very effective to evacuate the rectum before surgery or radiology

Disadvantages:

• 1. Inconvenient

• 2. Embarrassing

• 3. Slow and Erratic absorption

• 4. Irritation or inflammation may occur in the mucosal membrane

B. Bronchial Route of Drug Administration:

It is a local route where the drug is given into the respiratory tract by inhalation or insufflation. Gases, volatile liquids, and solids are inhaled, while non-volatile drugs are given as insufflations. It produces a local effect in the bronchi and is administered using an aerosol or nebulizer.

Advantages:

• 1. Local delivery of the drug

• 2. Quick absorption due to the large surface area of the lungs,

• 3. Higher concentration of the drug at the site of action

• 4. Quick onset of action,

• 5. No first-pass metabolism

• 6. A low dose is required

• 7. Low cost of medication

• 8. Low systemic side effects

Disadvantages:

• 1. Inconvenient process

• 2. Require proper training

• 3. Time-consuming

• 4. Wastage of the drug. Only 1-2% of drugs enter the bronchi,

• 5. Respiratory tract symptoms restrict medication

• 6. Expensive dosage form

• 7. May produce irritation in the pulmonary mucosa

• 8. Irritant drug increases pulmonary secretion.

• 9. Most preferred route for drug abuse (However, it will come under systemic absorption)

C. Nasal Route: It is a local route where drugs are given through the nose to produce local effects, like decongestant drops. Oxytocin spray can produce a systemic effect, but this use is rare.

D. Rectal Route: It mainly produces a local effect but can also provide a systemic effect due to the rectum’s rich blood supply. Drugs like diazepam, indomethacin, and chlorpromazine can be given by this route.

SYSTEMIC ROUTE OF DRUG ADMINISTRATION

The systemic route of drug administration can be divided into the following two parts

1. Enteral Route of Drug Administration

2. Parenteral Route of Drug Administration

Enteral Route (Oral Route) of Drug Administration:

It is the oldest, safest, and most common method of drug administration. Dosage forms like tablets, capsules, or liquids are taken by mouth and absorbed through the GIT for systemic effect.

Advantages:

• 1. Natural route

• 2. Convenient

• 3. Potable

• 4. No change in patient activity

• 5. Self-administration

• 6. No need for assistance,

• 7. Most suitable for repeated administration

• 8. Most suitable for prolonged use of the drug

• 9. Economical

• 10. Safe, Drug can be withdrawn after administration

• 11. Variety of dosage forms available

• 12. No pain or fear during administration

Disadvantages:

• 1. Irritable and non-palatable drugs are not accepted by the patient.

• 2. Irritation of the GIT may produce vomiting.

• 3. Not suitable in unconscious, uncooperative, vomiting, or diarrhoea.

• 4. Not suitable for children and elderly patients.

• 5. Drugs undergo first-pass metabolism. Like:

• a. Gastrointestinal juice may destroy drugs. Example: Insulin is destroyed by gastric juice.

• b. Liver destroys drugs.

• 6. GI contents hinder drug absorption. For example, calcium in the GIT prevents tetracycline and iron absorption.

• 7. GIT pH variation affects drug absorption. Aspirin absorption is retarded by high pH.

• 8. Irregular rate of drug absorption

• 9. A high dose is needed due to first-pass metabolism and slow absorption.

• 10. A large dose of the drug cannot be administered

• 11. Slow onset of action, thus not suitable in an emergency

Dosage form modifications can reduce some disadvantages —

• 1. Irritant drugs can be given in capsules or coated tablets,

• 2. Bitter drugs can be sugar-coated or flavored for better acceptability.

• 3. Enteric coating protects acid-sensitive drugs, such as erythromycin, from gastric acid.

Oral, sublingual, and rectal routes are all enteral if the drug enters systemic circulation.

Sublingual Route of Drug Administration:

Sublingual means under the tongue. The drug is placed under the tongue and absorbed through the mucosa. Ex. Glyceryl trinitrate.

Advantages:

1. Quick drug absorption into systemic circulation.

2. Quick onset of action

3. Very effective in an emergency

4. No destruction due to gastric juice and intestinal juice

5. No destruction in the Liver

6. Thus, no first-pass metabolism

7. Low dose required

8. After the desired effect, the drug may be spit out.

9. Fastest Routes of Drug Administration

PARENTERAL ROUTE OF DRUG ADMINISTRATION

Routes of administration other than the enteral route are parenteral. The drug is administered directly into the systemic circulation or tissue fluid.

Advantages

• 1. Quick onset of action due to elimination of the absorption factor

• 2. Useful in an emergency

• 3. Low dose of the drug due to the elimination of the absorption factor

• 4. Useful in an unconscious patient

• 5. Useful in an uncooperative patient

• 6. Useful during diarrhoea

• 7. Useful during vomiting

• 8. Uniform concentration of the drug in the blood produces uniform action

• 9. IV route is suitable for a large dose of the drug.

Disadvantages:

• 1. Inconvenient route of drug administration.

• 2. Psychological fear in the patient

• 3. Painful

• 4. Self-administration is difficult and usually requires paramedical assistance, except for insulin injections.

• 5. Not safe, the drug, once administered, cannot be withdrawn

• 6. Infection may occur, like hepatitis. AIDS

• 7. Injection may be contaminated, which will be harmful to the patient

• 8. Disposable syringes will be required to make it safer and free from infection.

• 9. More expensive because sterilisation and aseptic technique will be required to avoid contamination.

• 10. Nerve and other tissues may be injured.

Parenteral route includes the following routes of drug administration

1. Intradermal Route:

The drug is injected into the dermis layer of the skin either by raising a small bleb (e.g., BCG vaccine, penicillin allergy test) or by making multiple superficial punctures (e.g., smallpox vaccine). It is also called inoculation. This route is used only in special cases, allows administration of small and dilute doses, is painful, and the drug is absorbed mainly through the lymphatic system.

2. Subcutaneous Route:

The drug is injected into the subcutaneous tissue, where absorption is slow but uniform due to low vascularity, resulting in a prolonged duration of action. Oily solutions and aqueous suspensions can be used. The enzyme hyaluronidase may be added to enhance absorption. The dose should not exceed 2 mL, and patients can be trained for self-administration.

This route is reliable, but irritant drugs are avoided as the tissue is rich in nerves. In shock conditions, vasoconstriction reduces absorption. Repeated injections at the same site may cause lipoatrophy, leading to irregular absorption.

Methods:

• Dermojet: A needleless, high-pressure injector delivering the drug painlessly into subcutaneous tissue—ideal for mass inoculations.

• Pellet implant: A drug pellet is inserted subcutaneously through a small incision and stitched, allowing slow, prolonged release (e.g., testosterone, DOCA).

3. Silastic implants:

A Silastic tube containing a drug is implanted subcutaneously. It releases the drug slowly, and the drug is delivered into the blood for a longer duration.

Silastic tube is a non-biodegradable implant; thus, it has to be removed.

4. Intramuscular Route (IM):

The drug is injected into large skeletal muscles such as the deltoid, triceps, gluteus maximus, or rectus femoris. These muscles have a rich blood and lymph supply, allowing rapid and uniform drug absorption with minimal irritation. Absorption is faster from the deltoid than the rectus femoris, while in children, the rectus femoris is preferred due to underdeveloped gluteal muscles. The deltoid is used for small volumes (1–2 mL), and the gluteus for larger ones (up to 10 mL). Aqueous solutions are absorbed quickly, whereas oily or suspension acts slowly. Irritating drugs like quinine are injected deep into the muscle. Although reliable and fast, the IM route may cause pain, abscess formation, or nerve injury if injected improperly.

5. Intravenous Route:

In this route, the drug is injected directly into a superficial vein, allowing it to enter the bloodstream and produce an immediate effect. Only aqueous solutions are suitable; oily or suspension forms are not used. Possible complications include thrombophlebitis, tissue necrosis, air embolism, and a sudden drop in blood pressure. It is a risky route, especially for the brain and heart, due to possible drug accumulation.

Methods of Administration:

• a. Bolus: A large dose of the drug is dissolved in a suitable vehicle and injected slowly at once.

• b. Slow Infusion: A large volume of solution (e.g., dextrose or saline) is infused slowly, usually 1 L over 3–4 hours, to maintain a constant plasma concentration (e.g., oxytocin).

Advantages:

• a. Most suitable in an emergency because the drug will be immediately available at the site of action

• b. 100% bioavailability

• c. A large volume of the drug can be administered

• d. An irritant drug can be administered because the drug is immediately diluted and washed out from the site of administration.

• e. Dose can be adjusted rapidly. Infusion can be stopped immediately. Infusion rate can be increased if required.

6. Intraperitoneal:

The peritoneum has a large surface area. In infants, fluids are given intraperitoneally. This route is used to study drug effects in animals.

7. Intrathecal:

Injection of a drug in the subarachnoid space of the CNS is the intrathecal route of drug administration.

8. Intramedullary:

Injection of a drug into the bone marrow is called the intramedullary route of drug administration. It is very painful and rarely used.

9. Transmucosal:

Drugs are absorbed across the mucosal membrane. Sublingual route, nasal routeand rectal route are under the transmucosal route.

10. Transdermal Route:

Used for highly lipid-soluble drugs for absorption through the skin. Provides slow, prolonged absorption. Dosage forms include adhesive units, inunctions, iontophoresis, and jet injections.

• a. Adhesive Unit: It is available in the form of patches of different sizes and shapes. The drug is absorbed at a constant rate and is predictable.

• b. Inunction: Drug is rubbed on the skin to be absorbed to produce a systemic effect

• c. Iontophoresis: By this method lipid-insoluble drug can be administered into deeper tissues. Here, galvanic current is used to produce deep penetration of the drug,

• d. Jet injection: Dermojet is a form of transdermal route of drug administration.