Routes of drug administration: Systemic and Local/Topical Routes. Their advantages and disadvantages. Nursing, Medical, Pharmacy, USMLE, NCLEX, KAPS, NPLEX, GPAT, Exit Exam.

ROUTE OF DRUG ADMINISTRATION

Route means way from one place to another place. Administration means arrangement to control operation. “Route of drug administration is path through which drug or any substance enters into body or body fluid circulation”.

Following factors decide route of drug administration:

1. Doctor choice.

2. Routine treatment or emergency treatment

3. Therapeutic objective

4. Site of Action: Local or Systemic

5. Drug characteristics and its properties

6. Patient condition

7. Patient age

8. Patient preference

Route of drug administration can be divided into following types:

1. Local Route of Drug Administration

2. Systemic Route of Drug Administration

LOCAL/TOPICAL ROUTE OF DRUG ADMINISTRATION

The drug is applied at the site of drug action such as the skin or mucous membrane.

• · Topical route of drug administration means application of drug on the mucous membrane (eyes, nose, mouth, etc.) or skin surface. Cream, lotion, ointment, foam, eye drops, ear drops, etc are in dosage forms for topical application.

• · Local route refers to drug administration near the site of application. Examples are the administration of injection into muscle joints to produce local effects. An example is infiltration anesthesia. It is intended for local effect but may produce a systemic effect.

The following sites are used for topical/local application of drug/dosage forms

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

2. Gastrointestinal tract: Antacid, GIT sterilization before surgery

3. Rectum: Enema, Suppository.

4. Vagina: Enema, Suppository, Douches

5. Urethra: Bougie, Pessary

6. Anal canal: Enema, Suppository.

a.Enema: The drug is administered in liquid form. It may be an evacuate enema (like soap water enema) or retention enema in the treatment of ulcerative colitis.

b. Suppository: The drug is administered in solid form.

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

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

9. Skin: Ointment, Lotion, Cream, Powder

10. Transdermal Patches

11. Artery: The intra-arterial route is rarely used. It is used for diagnosis of disease like in coronary angiography. Some anticancer drugs are used to treat cancer. Drug is administered in arteries that supply drugs to cancerous cells.

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

LOCAL ROUTE OF DRUG ADMINISTRATION

The following are some commonly used local routes of drug administration.

A. Rectal, Vaginal And Urethral Routes Of Drug Administration have the following advantages and disadvantages:

Advantages:

1. Useful in unconscious patients

2. Useful in vomiting condition

3. Useful in children

4. No first-pass metabolism of the drug

5. Higher drug concentration at site of action

6. Very effective in evacuating 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: The drug is inhaled or insufflated into the respiratory tract. Generally gas, volatile liquid, or volatile solid are administered as inhalation. Non volatile drugs can also be administered as insufflations. This route is used to produce a local effect in bronchi. Aerosol or nebulizers are used for drug administration.

Advantages:

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

2. The quick onset of action,

3. No first-pass metabolism

4. Local delivery of drug

5. Higher concentration of drug at the site of action

6. A low dose is required

7. Low cost of medication

8. Low systemic side effects

Disadvantages:

1. Require proper training

2. Inconvenient process

3. Expensive dosage form

4. Time-consuming

5. It may produce irritation in the pulmonary mucosa

6. Wastage of drugs. Only 1-2% of drugs enter into bronchi

7. Irritant drug increases pulmonary secretion.

8. Respiratory tract symptoms restrict medication

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

C. Nasal Route: Drugs are administered through the nasal route. It is used to produce local effects such as decongestant nasal drops. However, oxytocin spray is used to produce systemic infection. However, it is rarely used to produce systemic effects.

D. Rectal Route: Generally it is used to produce local effects. But it can also be used to produce systemic effects. The rectum wall is rich in blood supply. Drugs can easily cross the mucosal layer to enter into blood. Drugs like diazepam, indomethacin, chlorpromazine, etc can be administered through 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 of Drug Administration: It is also called the oral route of drug administration. It is the oldest, safest, and most common route of drug administration. Drugs are administered to be absorbed from the gastrointestinal tract to produce systemic effects. Drugs are administered in dosage forms like tablets, capsules, liquid preparations, etc through the mouth.

Advantages:

1. Natural route

2. Convenient

3. Potable

4. No pain

5. Self-administration

6. No need for assistance,

7. Safe, The Drug can be withdrawn after administration

8. Economical

9. A variety of dosage forms are available

10. Most suitable for repeated administration

11. Most suitable for prolonged use of the drug

12. No change in patient activity

Disadvantages:

1. Irritable and nonpalatable drugs are not accepted by the patient

2. Drugs undergo first-pass metabolism. Like:

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

3. The liver destroys drugs.

4. Drug absorption may be delayed or stopped by gastrointestinal contents. Tetracycline absorption is stopped by calcium in GIT. Calcium delays or stop the absorption of iron.

5. Gastrointestinal pH variation affects drug absorption. Aspirin absorption is retarded by high pH.

6. A large dose is required due to first-pass metabolism and delayed absorption

7. Irregular rate of drug absorption

8. Large doses of the drug cannot be administered

9. Irritation with GIT may produce vomiting

10. Slow onset of action thus not suitable for emergency

11. Not suitable in unconscious patient, uncooperative patient, vomiting, diarrhea,

12. Not suitable for children and elderly patients.

Enteric coating protects drugs from acidic damage or gastric enzyme damage. Like erythromycin. Bitter drugs may be administered in sugar-coated tablet form. Usually, the oral route is considered an enteral route. However, if drugs are absorbed in the systemic circulation, the Sublingual and rectal routes will also be the enteral route.

Sublingual Route of drug administration: Sublingual means under the tongue. Drug is placed under the tongue and drug is absorbed through mucosa under the tongue. Ex. Glyceryl trinitrate.

Advantages:

1. Very quick drug absorption into the systemic circulation.

2. The very quick onset of action

3. Very effective in 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 doses require

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 considered as a parenteral routes. The drug is administered directly into the systemic circulation or tissue fluid. This route eliminates the absorption factor and first-pass metabolism.

Advantages

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

2. Useful in emergency

3. A 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 diarrhea

7. Useful during vomiting

8. The uniform concentration of drugs in the blood produces uniform action

9. Large doses of the drug can administered by IV route.

Disadvantages:

1. Self-administration of drugs is difficult. Assistance of paramedical staff is required for drug administration. Insulin injection is exceptional.

2. Inconvenient route of drug administration.

3. Psychological fear in the patient

4. Painful

5. Not safe, drug once administered cannot be withdrawn

6. Infection may occur like hepatitis. AIDS

7. The injection may be contaminated and will be harmful to the patient

8. More expensive because sterilization and aseptic techniques will be required to avoid contamination.

9. Disposable syringes will be required to make it more safe and free from infection.

10. Nerve and other tissues may be injured.

Parenteral route includes

1. Intradermal: The drug is administered into the dermis layer of the skin. The drug is administered into the skin by

a. Raising a bleb. Ex BCG vaccine, test for allergy sensitivity of penicillins or

b. By multiple superficial punctures or scaring of the epidermis, Ex smallpox vaccine.

Only small quantities and highly dilute drugs can be administered by this route. It is a painful route. The drug is absorbed through the lymphatic route.

2. Subcutaneous: The drug is injected into subcutaneous tissues. The dose should not exceed 2ml. Various modes are available for subcutaneous injection.

a. Dermoject: It is a high-pressure needleless injection. Drugs can be delivered quickly in the subcutaneous layer painlessly. It is most suitable for mass inoculation because it does not contact with the skin.

b. Pellet implant: The Pellet is implanted into the subcutaneous layer by incision and then stitched. Various hormonal drugs are administered by this route. Ex testosterone, desoxy corticosterone acetate (DOCA).

c. Sialistic implants: A silaistic tube containing the drug is implanted subcutaneously. It releases the drug slowly and the drug is delivered into the blood for a longer duration. The plastic tube is a nonbiodegradable implant thus it has to be removed.

Advantages: Subcutaneous is less vascular, thus drug absorption is slow but uniform. It prolongs the duration of action. The rate of absorption can be enhanced by the addition of the enzyme hyaluronidase. The patient can self-administer the drug.

Disadvantages: Subcutaneous tissue is rich in nerve thus irritant drugs cannot be administered by this route. In shock conditions, vasoconstriction takes place. Thus in shock conditions drug absorption through the subcutaneous route is not reliable. Repeated administration of drugs at the same site can cause lipoatrophy. It results in irregular absorption of the drug.

3. Intramuscular: The drug is administered into large skeletal muscles like the deltoid, triceps, gluteus maximus, rectus femoris, etc. The rate of absorption from the deltoid region is faster than the rectus femoris, especially in women. Rectus femoris is preferred in children because the gluteus is not well developed. Deltoid muscles are used for smaller volumes of drug usually 1-2 ml. For larger volume gluteus muscle is preferred. The volume of injection should not exceed 10ml. Generally aqueous solution is administered. Its absorption is faster. Oily solution and suspension are slowly absorbed. Irritating and painful drugs are injected into deeper parts of muscles ex. Quinine injection. While normal drugs are administered in the superficial part of muscles.

Advantages: Skeletal muscles are rich in lymphatic supply with low nerve fibers. It is a reliable route with rapid rate of absorption.

Disadvantages: It is painful and may cause abscesses. There is a risk of nerve damage if the drug is injected near the nerve. The needle may puncture blood vessels. Entry of drugs in a vein may be fatal.

4. Intravenous: The drug is injected into a superficial vein. Thus drugs directly enter into blood circulation to produce immediate effect. The drug can be administered in the following three manners

a. A blous: Bolus means lump. A large dose of the drug is administered. This drug is dissolved in a large volume of vehicle then it is administered slowly.

b. Slow Infusion: A large volume of drug is administered through slow infusion ex.

Dextrose, saline. Generally, one liter of injectable is administered in 3-4 hours. The rate of infusion also depends upon the patient's health condition. It is also preferred if constant plasma concentration of a drug is to be maintained for a longer duration ex. 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 drugs can be administered

d. Irritant drugs can be administered because the drug is immediately diluted and washed out from the site of administration.

e. Dose can be adjusted rapidly. The infusion rate can be increased, decreased, or stopped immediately.

Disadvantages:

a. Only aqueous solution can be administered through the IV route.

b. Suspension or oily preparation cannot be administered by this route.

c. Thrombophlebitis in the vein and necrosis in surrounding tissues may occur.

d. Air embolism may occur that may be fatal.

e. Rapid infusion may produce low blood pressure.

f. It is a risky route especially for the brain and heart because drugs may accumulate in these organs which may be fatal.

5. Intraperitoneal: Peritoneum has a large surface area. In infants, Fluids are injected intraperitoneally. It is usually preferred to study the effect of drugs in animals.

6. Intrathecal: Injection of the drug in the subarachnoid space of CNS is an intrathecal route.

7. Intramedullary: The injection of drugs into bone marrow is called an intramedullary route.

8. Transmucosal:. Sublingual, nasal and rectal route are under transmucosal route. Drugs are absorbed across mucosal membrane.

9. Transdermal Route: It is used for highly lipid-soluble drugs. The drug is slowly absorbed for a longer duration through the skin. The following dosage forms are used to administer the drug through the transdermal route.

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

b. Inunction: The drug is rubbed on the skin to be absorbed.

c. Iontophoresis: Here Galvanic current is used to produce deep penetration of the drug. Lipid-insoluble drugs are administered into deeper tissues through iontophoresis.

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