Pharmacology: Routes of Drug Administration
Intended Learning Outcomes
By the end of this lecture, you should be able to:
1. Understand the factors that govern the selection of drug administration routes.
2. Classify the different routes of drug administration.
3. Describe the advantages and disadvantages of these routes.
Key Factors Influencing the Choice of Route
1. Drug Properties:
- Physical form (solid, liquid, gas).
- Solubility, stability, pH, and irritancy.
2. Site of Action:
- Localized and accessible vs. generalized and less accessible.
3. Absorption:
- Rate and extent of absorption via various routes.
4. First-Pass Metabolism:
- Degradation by digestive enzymes or the liver before reaching systemic
circulation.
5. Response Speed:
- Rapid response required (e.g., emergencies) vs. routine treatment.
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6. Patient Condition:
- Suitability for unconscious, vomiting, or cooperative patients.
7. Dosage Precision:
- Routes like intravenous or inhalational allow accurate dosing.
Classification of Routes
1. Local Routes: Limited to a specific site for localized action with minimal
systemic absorption.
2. Systemic Routes: Drug is absorbed into the bloodstream for distribution
throughout the body.
Local Routes
Advantages: High drug concentration at the target site, minimal systemic side
effects, convenient application.
Disadvantages: Limited to accessible sites, unsuitable for deep or generalized
conditions.
1. Topical:
- Application on the skin or mucous membranes (e.g., eyes, ears, nose, throat).
- Examples:
- Skin: Ointments, creams, transdermal patches.
- Oral cavity: Nystatin suspension for oral candidiasis.
- Bronchi: Inhalation of salbutamol for asthma.
2. Deeper Tissues:
- Injections into specific tissues for local action.
- Examples:
- Intra-articular hydrocortisone for joint inflammation.
- Intrathecal lidocaine for spinal anesthesia.
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3. Arterial Supply:
- Intra-arterial injections for localized effects in specific tissues.
- Example: Anticancer drugs in limb malignancies.
Systemic Routes
Advantages: Wide distribution, suitable for generalized conditions, and various
formulations available.
Disadvantages: Potential systemic side effects, slower action (oral), and invasive
techniques (parenteral).
1. Oral (Ingestion):
- Most common and convenient route.
- Examples: Tablets, syrups, capsules.
- Advantages: Non-invasive, cost-effective, suitable for long-term use.
- Disadvantages:
- Slow onset (requires absorption).
- Unsuitable for irritant drugs, unconscious patients, or drugs degraded by
gastric juices (e.g., insulin).
2. Sublingual and Buccal:
- Drugs placed under the tongue or against the cheek for rapid absorption.
- Examples: Glyceryl trinitrate (angina), desaminooxytocin.
- Advantages:
- Quick onset of action.
- Avoids first-pass metabolism.
- Disadvantages:
- Unsuitable for irritant or lipid-insoluble drugs.
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3. Rectal:
- Used for systemic absorption or local effects.
- Examples: Diazepam (seizures), suppositories for vomiting patients.
- Advantages: Useful for unconscious or vomiting patients.
- Disadvantages: Inconvenient, unpredictable absorption, potential irritation.
4. Cutaneous (Skin):
- Highly lipid-soluble drugs for slow and prolonged absorption.
- Example: Transdermal patches for glyceryl trinitrate.
- Advantages: Convenient, bypasses first-pass metabolism.
- Disadvantages: Potential for local irritation.
5. Inhalation:
- Gases or volatile drugs absorbed via the lungs.
- Examples: General anesthetics, bronchodilators (e.g., salbutamol).
- Advantages: Rapid onset, minimal systemic toxicity.
- Disadvantages: Local irritation, bronchospasm.
6. Parenteral (Injection):
- Administered via injection, bypassing the digestive system.
- Types:
- Subcutaneous (s.c.): For slow absorption, small volumes (e.g., insulin).
- Intramuscular (i.m.): Faster absorption for mild irritants (e.g., depot
injections).
- Intravenous (i.v.): Immediate effect, 100% bioavailability (e.g., dopamine
infusion in shock).
- Advantages:
- Suitable for emergencies and unconscious patients.
- Avoids digestive enzymes and first-pass metabolism.
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- Disadvantages:
- Painful, requires sterile techniques, costly.
- Risks: Tissue injury, systemic toxicity, infection.
Parenteral Route in Depth
1. Subcutaneous (s.c.):
- Example: Insulin injections.
- Advantages: Self-administration possible, prolonged absorption.
- Disadvantages: Limited to small volumes, unsuitable for irritants.
2. Intramuscular (i.m.):
- Example: Vaccines, depot injections.
- Advantages: Rapid absorption, suitable for oily suspensions.
- Disadvantages: Painful, risk of abscess or hematoma.
3. Intravenous (i.v.):
- Example: Emergency drugs like diazepam for seizures.
- Advantages: Fastest action, precise dosing, suitable for emergencies.
- Disadvantages: Most risky route due to potential for necrosis, systemic toxicity,
and infection.
