Introduction
Routes of drug administration are the pathways through which a drug enters the body. The selection of a suitable route depends on the drug’s properties (like solubility and stability), the desired speed of action, patient condition and the therapeutic goal. Drug administration routes are broadly classified into enteral, parenteral and other specialized routes.
A) Enteral Routes
Enteral administration involves delivering the drug through the gastrointestinal (GI) tract. It is one of the safest, most convenient and economical routes.
1. Oral Route
Oral administration means swallowing the drug. It is easy, self-administered and has a low risk of infection. Overdose can also be managed using antidotes like activated charcoal.
Limitations
- Slow absorption.
- Drugs may be destroyed by stomach acid (e.g., proteins).
- First-pass metabolism reduces drug effect.
Oral Preparations
- Enteric-coated tablets: Have a protective coating that prevents dissolution in the stomach. Useful for acid-sensitive drugs like omeprazole and for medicines irritating to the stomach such as aspirin.
- Extended-release formulations: Release the drug slowly over time, improving compliance. Example: extended-release morphine.
2. Sublingual Route
The drug is placed under the tongue and absorbed directly into systemic circulation through capillaries.
Advantages
- Rapid absorption.
- Avoids first-pass metabolism.
- Useful for emergency situations (e.g., nitroglycerin in angina).
3. Buccal Route
The drug is placed between the cheek and gum. It provides slow, steady absorption and avoids first-pass metabolism.
B) Parenteral Routes
Parenteral administration bypasses the GI tract by delivering drugs directly into body tissues or bloodstream. These routes give quick action and high bioavailability but require sterile technique and trained personnel.
1. Intravenous (IV)
The drug is injected directly into the bloodstream.
Advantages
- Immediate effect.
- Precise control of drug levels.
- Useful for drugs that are poorly absorbed orally (e.g., atracurium).
Disadvantages
- Risk of infection.
- Cannot be recalled once given.
- Risk of toxicity if given too rapidly.
2. Intramuscular (IM)
The drug is injected into large muscles. Absorption is moderate to fast depending on the formulation.
Types
- Aqueous solutions: Absorbed quickly.
- Depot preparations: Slow release, e.g., depot medroxyprogesterone, haloperidol decanoate.
3. Subcutaneous (SC)
The drug is injected into the loose tissue under the skin.
Advantages
- Slower, sustained absorption.
- Less risk of hemolysis than IV.
Limitations
- Not suitable for irritant drugs.
- Pain or necrosis may occur.
C) Other Routes of Drug Administration
1. Inhalation Route
Drugs are inhaled through the mouth or nose. Absorption is rapid due to the large surface area of the respiratory tract.
Uses
- Gases like anesthetics.
- Aerosols for asthma, such as albuterol or fluticasone.
2. Nasal Route
Drugs are sprayed into the nose. It is useful for local and systemic effects.
- Decongestants like oxymetazoline.
- Hormones like desmopressin.
- Calcitonin nasal spray for osteoporosis.
3. Intrathecal / Intraventricular
Drugs are injected directly into cerebrospinal fluid to bypass the blood-brain barrier.
- Used in severe CNS infections, e.g., intrathecal amphotericin B.
4. Topical Route
Applied to skin or mucous membranes for local action.
- Skin creams (e.g., clotrimazole).
- Ophthalmic and ear preparations.
5. Transdermal Route
Drugs are delivered through the skin for systemic action using patches.
- Nitroglycerin patch.
- Nicotine patch.
- Scopolamine patch for motion sickness.
6. Rectal Route
Drugs are administered as suppositories or enemas.
Advantages
- Useful when patient is vomiting or unconscious.
- Avoids stomach acid and partially avoids first-pass metabolism.
Limitations
- Absorption may be irregular.
- Some drugs irritate rectal mucosa.
Detailed Notes:
For PDF style full-color notes, open the complete study material below: