Routes of drug administration plays an important role to obtain maximum benefit from the drug. Drug administered into the body goes through several metabolic changes which affect the bioavailability of drug. Bioavailability is the proportion of drug that is available at site of action. Therefore, route of administration is important for maximum bioavailability. An intravenous route of administration has 100% bioavailability.
The choice of route of administration is depend on various factors which include:
- Effect of gastric pH, digestive juices and first pass metabolism.
- Convenience of the patient
- Desired onset of action
- Physical and chemical properties of drugs.
There are different routes of drug administration as follows,
Oral/ Enteral route
This is the most common and easiest route of administration. Dosage forms administered orally include tablets, capsules, syrups, powders, suspension, etc.
The oral route is most convenient, cheap and safe method of administration. Hence it is considered as the first choice of drug administration. The orally administered drug goes through first pass metabolism by liver. Hence the actual concentration of drug reaching to bloodstream is less.
- It is safe method of drug administration.
- It is convenient.
- It is cheap.
- Onset of action is very slow.
- Some drugs have gastrointestinal tract irritation.
- It is not useful in conditions like nausea, vomiting, emergency situation and unconscious patients.
- As drug is gone through first pass metabolism, high dose is required for desired action.
Sublingual and Buccal route of administration
Sublingual is the Latin term which means under the tongue. The mucous membrane under the tongue is supplied with large number of blood capillaries. Hence the drug directly enters into the systemic circulation. This route of administration has faster rate of absorption as compared to oral route. The sublingual route of drug administration bypasses the first pass metabolism.
Patients must be instructed to not to swallow tablets and avoid immediate consumption of water to ensure proper absorption of drug. For example, nitroglycerine, buprenorphine.
In buccal route of administration, medicine is placed between the gums and the inner lining of the cheek. For example, fentanyl buccal patches
Both route of administration has same advantage and disadvantage, only the site of action is different.
Advantages of sublingual and buccal route of administration
- Onset of action is faster than oral route.
- Excess drug can be easily spit out.
- 100% bioavailability can be achieved.
Disadvantage of sublingual and buccal route of administration
- Large quantity of dose cannot be administered.
- It is irritating if there are any existing open sores in the mouth.
- Medicine effect get reduced if it is swallowed.
This route of administration is useful in patients having vomiting, in unconscious patients who are unable to take tablets orally, when dug has unpalatable taste or odor, when drug can be destroyed by digestive enzymes.
The drugs given by rectal routes absorbed by rectums blood vessels and reach to bloodstream. Suppositories and enemas are the common dosage forms used in rectal route of administration.
- This route is helpful in children and elderly patients.
- It is useful when oral route of administration is not useful.
- The less amount of drug gets degraded as compared to oral route of administration.
- It is possible to give large quantity of dose.
- It is uncommon and unacceptable by most of the patients.
- Some drugs cause rectal irritation and proctitis, which may develop to ulceration or bleeding.
Parenteral route of administration
The term parenteral route of administration refers to any other route of administration than the digestive tract. But the most commonly used parenteral route of administration are intravenous (IV), intramuscular (IM) and subcutaneous (SC).
- Rapid onset of action.
- 100% bioavailability achieved.
- The best way for the patients who cannot ingest anything orally.
- Chances of infection
- Not suitable for oily and insoluble preparations
- Skilled person required to perform
Intravenous route (IV)
In this route of administration medicine is directly administered into the systemic circulation. This route is selected when a rapid effect is desired or when drug is poorly absorbed from the digestive tract. It is also useful in patients with severe nausea and vomiting or patients with unstable mental status.
Intramuscular route (IM)
In this route of drug administration, medicine is directly injected into the muscles. Muscles are highly vascular in nature. Oily, slow releasing and irritant preparations are given by intramuscular route. Injection sites include upper arm, buttocks or thigh.
Subcutaneous route (SC)
In this route medicine injected into fatty tissue just below the dermis of skin. Then medicine moves into the small blood vessels and reach to blood stream. It is easy to administer and requires minimal skills, so patients can self-administer the medicine, example insulin.
Other routes of drug administration
Medicine is administered by inhaling through the mouth with the use of inhaler. In this route drug is directly passes into the lungs, which gives maximum therapeutic action. How much drug quantity reach to lungs is depended on the size of droplets of the medicine incorporated in inhaler. Smaller droplets go deeper which increases the amount of drug absorbed. For example, budesonide.
The intranasal route of drug administration involves the delivery of medicine through the nasal passages. It is an alternative route to traditional routes, offers a direct path to the bloodstream through the nasal mucosa. The main factor which affects the rate of drug absorption through nasal route is the rate of nasal secretion. The rate of nasal secretion is inversely proportional to the availability of the drug. Diseases affecting nasal mucous membrane can affect the drug absorption.
In this route of administration medicine is directly administered into the eyes. This is the specialized route designed to treat the eye disease and disorders like, glaucoma, conjunctivitis and eye injuries. Most of the ocular drugs used for their local effects. The medicine is absorbed through the cornea or conjunctiva.
In this route of administration medicine is directly administered into the ear. This route of administration is used to treat various ear conditions and disorders to treat local ailments of auditory system. Before applying otic medicines, patient should thoroughly clean the ear.
In this route of administration medicine is directly inserted into the vagina. The medicine is absorbed through the vaginal wall. Dosage forms like tablet, cream, gel, suppositories are used in this system.
In this route of administration medicine is directly applied on the skin. This is used for localised effects and to treat superficial skin disorders, such as dry skin, eczema, psoriasis and fungal/bacterial/viral infections. This route is helpful for both therapeutic and cosmetics use. Dosage forms like cream, lotion, ointment, solution and powder are used.
In this route of administration medicine is directly applied on the skin. The main difference between cutaneous route and transdermal is, cutaneous route is focuses on localised effect and transdermal route delivering medicine for systemic effect. Example, nitro-glycerine patches for chest pain.
The diverse route of drug administration comes with spectrum of options for healthcare professionals to treat their patients, based on medication nature and patients physical and mental status. As we have seen every route of administration comes with its unique advantages and disadvantages. Understanding these various routes of drug administration helps to effective use of drug and minimise their side effects.
Frequently asked questions
Which is the fastest route of drug administration?
Intravenous (IV) route is the fastest route of drug administration.
Which is the slowest route of drug administration?
Oral route is the slowest route of drug administration.
Which is the safest route of drug administration?
Oral route is the safest route of drug administration.
Can you drink water after sublingual medicine?
No, you cannot drink water after administering medicine by sublingual route, because it will hamper the absorption of medicine.
Why are the routes of drug administration important?
Understanding various routes of drug administration helps to effective use of drug and minimise their side effects.
What route is under the tongue?
In sublingual route of administration drug is placed under the tongue. Sublingual is the Latin term which means ‘under the tongue’.
Which route of drug administration gives 100% bioavailability?
Intravenous (IV) route gives 100% bioavailability.