Biopharmaceutics 1 (28/01/19)

Question 1

What is the process of tablets or capsules being made to granules or aggregates?

Answer 1

Disintegration

Question 2

What is the process of granules or aggregates being made into fine particles?

Answer 2

Deaggregation

Question 3

What is the Noyes-Whitney equation?

Answer 3

dm/dt = (DA(cs-c))/h

dm/dt: rate of dissolution (or change of mass over time)
D: diffusion coefficient
A: Surface area of particle
h: thickness of diffusion layer
cs: saturation concentration in the diffusion layer
c: concentration in the GI fluid

Question 4

What factors affect the dissolution rate?

Answer 4

Surface Area (affects particle size and porosity. increased by wetting agent)

Solubility of diffusion layer (cs) (weak acid solubility increases with increase in pH, Solubility in stomach < solubility in intestine)

drug in solution (c)

Diffusion of drug ( inversely proportional to viscosity)

Thickness of diffusion layet (h) (agigation dependent)

Crystal vs amorphous state (Amorphous will dissolve faster)

Solvates (generally, higher solvation degree, lower solubility)

Question 5

If absoption does not increase with dissolution (dm/dt) what does this mean?

Answer 5

It is NOT the limiting step.

Question 6

Explain the difference between “drug” and “medicine” and why we need to make the distinction

Answer 6

Drug =Active pharmaceutical ingredient (API), pharmacological agent, and/or therapeutic molecule

Medicine = dosage form, formulation, drug delivery system, Drug + excipent

Question 7

Define Absolute bioavailability

Answer 7

fraction of the drug in the dosage form that arrives in the systemic circulation

Question 8

Why does “available at the site of action” translate to arrives to the systemic circulation?

Answer 8

Practical reason – blood can be sampled easily. Most tissues are not accessible for sampling.
Pharmacokinetic theory – Blood is the central compartment from which drug is distributed.
Pharmacokinetic theory – Absorption is the process of drug entering the central compartment by a route of administration.
Pharmaceutics – once the drug is in the central compartment, the formulation is irrelevant; drug is now dissolved in blood plasma. Formulation is only relevant to absorption.

Question 9

What are the types of administration (ROA)?

Answer 9

1) Across epithelial layers (Skin, small intestine, bucal, gastric, rectal, nasal, bronchial)
2) Bypass epithelial layer via injection/parenteral (Intravascular/directly into blood: i/v, intra arterial) (extravascular/into other body tissue, from which drugs absorbed into local capillaries: SC, IM, and IP/intraperitoneal)

Question 10

Describe transdermal delivery and absorption

Answer 10

Absorption rate is low and occurs in capillary bed of dermis, but drug must first penetrate avascular epidermis

Question 11

What is stratum corneum?

Answer 11

Structure of tightly packed dead cells

Question 12

Advantage of transdermal drug absorption?

Answer 12

Long acting (hours to days), and no first pass metabolism

Question 13

Key features of Gastrointestinal drug absorption

Answer 13

• Large Surface area
• High permability (due to lipid bilayer, gaps between cells which asbsorbs hydrophillic drugs, and specific carrier systems can be exploited)