Biopharmaceutics — “Drug Form Matters”
Biopharmaceutics studies how the dosage form and formulation affect drug absorption.
Core Insight:
Even the best drug is useless if the body can’t absorb it properly.
Key Factors Biopharmaceutics Studies:
Drug Physicochemical Properties
- Solubility – Can the drug dissolve?
(If it can’t dissolve, it can’t be absorbed… simple.) - Permeability – Can it cross biological membranes?
- pKa & Ionization – pH conditions affect drug absorption.
- Particle size – Smaller = dissolves and absorbs faster.
Dosage Form Design
Different forms release drug differently:
- Tablet
- Capsule
- Suspension
- Solution (fastest)
- Controlled-release tablet
- ODT, SR, CR, XL, TD patches, suppositories — all release the drug at different speeds.
Excipients
Inactive ingredients, but they change everything:
- Disintegrants → break the tablet quickly
- Lubricants → may slow dissolution
- Polymers → create sustained release
- Surfactants → improve absorption
Absorption Site Factors
- Gastric emptying rate
- Intestinal motility
- pH of stomach & intestine
- Bile salts (help in fat-soluble drug absorption)
Goal of Biopharmaceutics
Predict how the formulation affects drug absorption and therapeutic effect.
In short:
Biopharmaceutics focuses on the dosage form → how fast & how much drug gets into the bloodstream.
Part 2: Pharmacokinetics — “What the Body Does to the Drug”
Here comes the main engine room.
Pharmacokinetics = ADME
- Absorption
- Distribution
- Metabolism
- Excretion
Let’s deep-dive.
Absorption — Drug entering the bloodstream
Process where the drug moves from site of administration → blood.
Factors controlling absorption:
- Route (oral, IV, IM, Subcut, rectal, transdermal)
- Solubility
- Membrane permeability
- Blood flow
- First-pass metabolism
Oral drugs face the biggest challenge → must survive acid, enzymes, liver first-pass effect.
Distribution — Drug spreads through the body
Once in blood, drug is distributed to tissues.
Influencing factors:
- Blood flow (brain, liver get high flow)
- Protein binding (albumin binding reduces free drug)
- Tissue affinity (fat-loving drugs store in adipose)
Distribution is measured as Vd (Volume of distribution).
Metabolism — Body transforms the drug
Mostly happens in the liver.
Phases:
- Phase I: oxidation, reduction, hydrolysis
(CYP450 enzymes) - Phase II: conjugation
(Glucuronidation, sulfation, acetylation)
Metabolism:
- Can activate a prodrug (e.g., codeine → morphine)
- Can detoxify drug for excretion
Excretion — Removing the drug
Main organs:
- Kidney (urine)
- Liver/bile (feces)
- Lungs (volatile anesthetics)
- Sweat, saliva, milk (minor)
Kidney excretion steps:
- Filtration
- Secretion
- Reabsorption
Pharmacokinetic Parameters
These are the corporate KPIs of drug movement:
✔ Cmax – peak concentration
✔ Tmax – time to reach peak
✔ AUC (Area Under Curve) – total drug exposure
✔ Half-life (t½) – time to reduce concentration by 50%
✔ Clearance (Cl) – rate of drug removal
✔ Bioavailability (F) – fraction of drug absorbed
How PK and BP work together
Biopharmaceutics
Decides how the drug enters the body.
Pharmacokinetics
Decides what happens next.
Think like this:
Dosage form → affects absorption → which controls PK → which determines effect.
Example:
A sustained-release tablet changes:
- absorption rate (slow)
- peak levels (lower)
- half-life effect (prolonged)
Practical Pharmacy View
These concepts help pharmacists predict:
- How fast a drug works
- How dosage changes affect patients
- Why two brands with same drug may act differently
- How food interactions change drug absorption
- Why liver/kidney patients need dose adjustment
MCQs — Pharmacokinetics & Biopharmaceutics
Bioavailability
Q1.
Which of the following routes has 100% bioavailability?
A. Oral
B. Rectal
C. Intravenous
D. Intramuscular
Correct Answer: C — Intravenous
Why?
IV gives drug directly into bloodstream → no absorption, no first-pass effect.
First-Pass Metabolism
Q2.
A drug with extensive first-pass metabolism will show:
A. Increased oral bioavailability
B. Decreased oral bioavailability
C. No change in Tmax
D. Higher Cmax
Correct Answer: B — Decreased oral bioavailability
Why?
First-pass reduces the amount reaching systemic circulation.
Absorption Rate
Q3.
Which dosage form will achieve the fastest absorption?
A. Enteric-coated tablet
B. Suspension
C. Solution
D. Sustained-release tablet
Correct Answer: C — Solution
Why?
Drug is already dissolved → no disintegration/dissolution needed.
Volume of Distribution (Vd)
Q4.
A drug has a very high Vd. What does this indicate?
A. Drug stays mostly in the blood
B. Drug is highly bound to plasma proteins
C. Drug distributes extensively into tissues
D. Drug is excreted unchanged
Correct Answer: C — Distributes extensively into tissues
Why?
High Vd = drug leaves blood & enters tissues (fat/liver/muscle).
Half-Life
Q5.
If the half-life of a drug is 8 hours, how much drug remains after 24 hours?
A. 12.5%
B. 25%
C. 50%
D. 6.25%
Correct Answer: A — 12.5%
Why?
24 hrs = 3 half-lives → 100 → 50 → 25 → 12.5%.
Clearance
Q6.
Clearance of a drug primarily depends on:
A. Bioavailability
B. Elimination processes
C. Drug solubility
D. Gastric emptying
Correct Answer: B — Elimination processes
Why?
Clearance = ability of body (kidney/liver) to remove drug.
Metabolism — Phase I
Q7.
Which of the following is a Phase I metabolic reaction?
A. Glucuronidation
B. Sulfation
C. Oxidation
D. Acetylation
Correct Answer: C — Oxidation
Why?
Oxidation = Phase I; others = Phase II.
Protein Binding
Q8.
A drug that is highly protein-bound will show:
A. More free drug in plasma
B. Lower risk of drug interactions
C. Lower Vd
D. Higher free fraction during hypoalbuminemia
Correct Answer: D — Higher free fraction in low albumin
Why?
Less albumin → more unbound drug → higher effects/toxicity.
Zero-Order Kinetics
Q9.
A drug that follows zero-order kinetics is characterized by:
A. Constant percentage eliminated per hour
B. Constant amount eliminated per hour
C. Rate dependent on concentration
D. No metabolism involved
Correct Answer: B — Constant amount per hour
Why?
Zero-order = fixed amount (e.g., phenytoin, alcohol).
Effect of Food
Q10.
Food may delay drug absorption by:
A. Increasing gastric emptying
B. Decreasing gastric emptying
C. Increasing dissolution rate
D. Altering pH to alkaline
Correct Answer: B — Decreasing gastric emptying
Why?
Food slows stomach movement → delays absorption.
Also read -Bioequivalence testing of generic drugs and special considerations for biopharmaceutical products