The absorption, distribution, and overall effect of a drug in the body depend on both the route of administration and the formulation used. Drugs are delivered in specific units called dosage forms, each tailored to optimize efficacy, stability, and patient compliance.
A dosage form refers to the physical form of a drug product suitable for administration. A single drug may be available in multiple dosage forms, each designed to modify how the drug is delivered and absorbed. Selection depends on patient needs, target effect location, and pharmacokinetics.
🔑 Local vs Systemic Effects
- Local Effect: Drug activity is limited to the site of application (e.g., topical cream).
- Systemic Effect: Drug enters systemic circulation and acts at distant sites (e.g., oral tablet, IV injection).
Dosage forms consist of:
- Active Ingredient: The pharmacologically active compound.
- Inactive Ingredients (Excipients): Substances included to aid manufacturing, stability, delivery, or absorption.
| Excipient Type | Purpose | Common Dosage Forms |
|---|---|---|
| Binders | Hold ingredients together in a cohesive unit | Tablets |
| Lubricants | Prevent sticking to manufacturing equipment | Tablets, Capsules |
| Disintegrants | Promote breakup of the dosage form after intake | Tablets, Capsules |
| Diluents | Add bulk to formulations for proper dosing | Tablets, Capsules, Lyophilized Powders |
| Preservatives | Prevent microbial growth | Liquids, Ophthalmics, Topicals |
| Flavoring Agents | Improve palatability | Oral Liquids, Chewable Tablets |
| Colorants | Aid in product identification | Tablets, Capsules |
| Solvents | Dissolve active ingredients | Solutions, Injectables |
| Coating Agents | Mask taste or control release | Enteric-coated, Extended-release tabs |
📌 Note: Not all excipients are inert for all patients. Some may cause allergies or intolerances.
A drug's solubility is its ability to dissolve in a solvent, typically water or biological fluids. This property directly influences absorption, especially for enteral and parenteral routes.
🔑 A drug must be dissolved before it can be absorbed into the bloodstream. Poor solubility often leads to poor bioavailability.
| Property | Effect on Drug Performance |
|---|---|
| High Solubility | Faster dissolution, quicker onset |
| Low Solubility | Slower or incomplete absorption |
📌 Solubility can be modified using salts, particle size reduction, or formulation with solubilizing agents.
Routes of administration are classified into two broad categories:
- Enteral: Administration involving the alimentary canal
- Parenteral: Administration bypassing the gastrointestinal tract
📌 Each route affects onset, bioavailability, and duration of action.