Biopharmaceutics is the study of how the physical and chemical properties of a drug, the type of dosage form, and the route of administration influence the rate and extent of drug absorption into the body. In simple terms, it explains how a drug moves from its dosage form into the bloodstream and eventually produces a therapeutic effect.
This subject helps pharmacists understand why some drug products work faster or better than others, why certain dosage forms are chosen, and how formulation problems can reduce drug availability.
What Is Biopharmaceutics?
Biopharmaceutics connects pharmacy, physiology, and pharmacokinetics. It focuses on how the body interacts with a drug before it enters systemic circulation. The core objective is to ensure that the drug reaches the blood in the right amount and at the right time.
Key Concepts in Biopharmaceutics
1. Pharmaceutical Phase
This phase includes what happens inside the dosage form before the drug dissolves. For solid dosage forms (like tablets):
- Disintegration → tablet breaks into granules
- Deaggregation → granules break into fine particles
- Dissolution → drug dissolves in GI fluids
A drug must dissolve before it can be absorbed.
2. Pharmacokinetic Phase
This phase covers:
- Absorption – movement of drug from its site of administration into the bloodstream
- Distribution – transport of drug into tissues and organs
- Metabolism – conversion into metabolites
- Excretion – removal from the body
3. Pharmacodynamic Phase
This phase involves how the drug interacts with receptors to produce therapeutic or toxic effects.
Bioavailability
Bioavailability is the fraction of an administered dose that reaches the systemic circulation in unchanged form. It depends on:
- Dissolution rate
- Absorption characteristics
- First-pass metabolism
- Drug–food interactions
- Formulation factors
For example, intravenous (IV) drugs have 100% bioavailability.
Factors Affecting Biopharmaceutics
1. Drug-Related Factors
- Solubility: poorly soluble drugs absorb slowly
- Particle size: smaller particles dissolve faster
- Lipophilicity: lipid-soluble drugs cross membranes easily
- Polymorphism: different crystalline forms dissolve differently
2. Dosage Form Factors
- Tablets vs capsules vs liquids
- Coatings (enteric, sustained-release, etc.)
- Excipients used in formulation
- Manufacturing methods
3. Physiological Factors
- Gastric emptying rate: faster emptying increases absorption
- GI pH: affects drug ionization and solubility
- First-pass effect: metabolism in liver before drug reaches circulation
- Blood flow to absorption site
Importance of Biopharmaceutics
Biopharmaceutics helps pharmacists and formulators answer important questions:
- Why does one tablet work faster than another?
- Why do some drugs fail to show expected therapeutic response?
- Why do certain patients respond differently to the same drug?
- How can we improve dosage forms to enhance bioavailability?
Applications in Pharmacy Practice
- Designing effective dosage forms
- Improving absorption characteristics of drugs
- Predicting therapeutic response
- Identifying formulation-related problems
- Selecting appropriate administration routes for patients
Biopharmaceutics vs Pharmacokinetics
Biopharmaceutics focuses on the drug before it enters the bloodstream (dissolution, absorption influences).
Pharmacokinetics deals with the drug after absorption (distribution, metabolism, elimination).
Detailed Notes:
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