Pharmacology: Drug Administration Routes

Introduction

• A drug is an agent used for diagnosis, treatment, cure, or prevention of disease in humans or animals.
• A successful therapeutic response occurs when a drug reaches the receptor site in sufficient concentration to exert its pharmacological action.
• Drug absorption into body tissues from the administration site depends on the required action (local or systemic) and speed of response.

The Oral Route

• Used for systemic or local effects.
• Drugs are administered in solid or liquid form.
• Absorption occurs in the gastrointestinal tract (G.I.T.).
• Advantages: Simplest, self-administration possible, safest.
• Disadvantages: Onset of action is slow, absorption is irregular, certain drugs are destroyed by enzymes/secretions in the G.I.T., drug solubility can be affected by substances like calcium, slow gastric emptying can cause drug inactivation, unsuitable for unconscious/vomiting patients.

The Buccal Route

• Drugs are administered as tablets.
• High vascularity of the tongue and buccal cavity, and saliva presence facilitate drug dissolution.
• Tablets formulated for this route provide a quick onset of action.
• Advantages: Relatively quick onset, direct absorption into systemic circulation (avoiding first-pass effect), suitable for unconscious patients, suitable for antiemetic drugs.

The Sublingual Route

• Absorption occurs under the tongue.
• Provides a very fast onset of action, but duration is typically short.

The Rectal Route

• Drugs are administered as liquids (enemas), solids (suppositories), or semisolids (creams/ointments).
• Used for both systemic and local effects.
• Some drugs absorbed in the rectum bypass the liver (first-pass effect), thus bioavailability may be less than 100%.
• Advantages: Useful when oral route is unsuitable (e.g., vomiting, unconscious patients), suitable for patients with G.I.T. irritation, can be used for local action.
• Disadvantages: Absorption can be irregular, less convenient than oral route, low patient acceptability.

The Vaginal Route

• Drugs are administered as pessaries, tablets, creams, ointments, or vaginal douches.
• Used for both local and systemic effects.
• Advantages: Drugs avoid the first-pass effect. Higher fluid content in the vagina leads to more efficient drug dissolution than the rectal route.

The Inhalation Route

• Drugs are inhaled through the nose or mouth.
• Used primarily for respiratory conditions, delivering drugs directly to the lungs.
• Advantages: Lower drug dose required for systemic effect compared to oral route, reduced side effects.

The Topical Route

• Skin is used as the administration site.
• Primarily for local effects.
• Formulations include ointments, creams, pastes, lotions, and recently developed transdermal patches (for systemic effects).

The Parenteral Route

• This describes drug administration via injection.
• Various routes include:
• Intravenous (IV): Direct injection into the systemic circulation, very fast onset of action.
• Intramuscular (IM): Injection into muscle tissue, relatively fast onset of action, especially with liquid formulations; slower/prolonged action possible with suspensions or oily forms.
• Subcutaneous (SC): Injection beneath the skin, easiest/least painful injection, slower onset of action, but prolonged action (e.g., insulin injections).
• Intradermal (ID): Injection into the skin between the dermis and epidermis, small volumes, often used for allergy testing and immunizations.
• Intra-arterial: Injection into an artery, primarily used for diagnostic purposes (e.g., X-ray contrast).
• Intra-spinal: Injection into the subarachnoid space, peridural space, or cisterna magna, used for spinal anesthetics.
• Intra-articular: Injection into the synovial fluid of a joint, used for localized corticosteroid administration for anti-inflammatory purposes.