39 Questions
What does Fick’s First Law of Diffusion state?
The rate of diffusion is proportionate to concentration gradient, cross-sectional area, and diffusion coefficient
What does the diffusion coefficient (D) measure?
The amount of solute diffusing across 1 cm$^2$ in 1 second
What does the term 'J' represent in the context of diffusion?
Flux, measuring the amount of substance that will flow through a unit area during a unit time interval
When does diffusion stop according to the provided text?
Diffusion stops when the concentration gradient (dc/dx)* equals 0
What is the main buffer system in the intestine?
Bicarbonate system
What is the approximate fasting pH range in the duodenum of the small intestine?
6.2-7.0
What is the fasting concentration of bile salts in the intestinal fluid?
3 mM
What is the fasting surfactant concentration of bile salts compared to the fed state?
Fasting is higher
What is the approximate ratio of bile salt to phospholipids in the intestinal fluid?
4:1
What is the approximate thickness of the unstirred water layer adjacent to the intestinal membrane?
30-50 µm
How much intestinal surface area is needed for sufficient oral absorption?
800 cm²
What is the in vivo effective permeability (Peff) of the intestine?
$10^{-4}$ cm/s
According to the Biopharmaceutical Classification System (BCS), which class represents substances with high solubility and high permeability?
Class I
What is the transit time of the stomach in the fasting state for drug absorption?
12 minutes
According to FDA guidance, what is the pH range for securing a waiver of in vivo bioavailability and bioequivalence studies for solid oral dosage forms?
1.2-6.8
What is the deciding factor for drug dissolution in orally administered products?
Solubility
What is the driving force for diffusion?
Frictional force exerted by viscosity of the solution
What is the function of the diffusion coefficient?
It is a function of temperature/viscosity and related to solute radius
What does Fick's 2nd Law of Diffusion explain?
The diffusion process and changes in concentration along the direction of diffusion
What happens when the concentration gradient decreases according to Fick's 2nd Law of Diffusion?
Diffusion slows down
What does Einstein's random walk theory determine?
The diffusion coefficient
How is the diffusion coefficient often experimentally measured?
In a two-chamber vessel separated by a porous membrane
What is the function of a diffusion cell?
To monitor the diffusion of a drug between donor and receptor chambers
What does passive diffusion involve?
Mass transfer of molecules based on a concentration gradient
What does sink conditions imply in diffusion?
Constant removal of drug in the receptor chamber and replacement of solvent
What is the goal of sink conditions in diffusion?
To drive concentration gradient to a constant
What does Fick's 1st Law of Diffusion explain?
Diffusion occurs according to a concentration gradient
What does Fick's 2nd Law of Diffusion predict?
How diffusion will cause a concentration change with respect to time
What is the primary objective of dissolution rate studies?
Assessment of oral drug absorption under physiological conditions
Which factor can influence the dissolution rate of drugs?
Agitation
What is the role of bile salts in drug dissolution?
Enhancing the solubility of lipophilic drugs
Which step is involved in drug dissolution from a solid dosage form?
Swelling
What does the Biopharmaceutical Classification System (BCS) utilize for dissolution studies?
250mL of dissolution fluid
How are dissolution tests carried out?
Under simulated in vivo sink conditions with constant replacement of the dissolution medium
What is the influence of excipients on drug dissolution?
They can increase or decrease the aqueous solubility of drugs
How does particle size affect drug dissolution rate?
Micronization of particles increases the dissolution rate and oral absorption
What is the role of diffusion layer thickness in drug dissolution?
The thickness decreases over time, leading to an increase in the intrinsic dissolution rate
What is the purpose of dissolution testing in drug quality control?
To determine the bioavailability of a drug
What is the significance of in vitro dissolution testing?
It is the most important quality control test for many pharmaceutical preparations
Study Notes
Drug Dissolution and Factors Affecting Dissolution Rate
- The process of drug dissolution is a kinetic process of solid particles going into solution, which is vital for determining the bioavailability of a drug in vivo.
- In vitro tests are used for drug quality control, with dissolution testing being the most important quality control test for many pharmaceutical preparations.
- Drug dissolution from a solid dosage form involves steps such as wetting, penetration of the solvent, swelling, disintegration, and dissolution of individual drug particles.
- Dissolution tests are carried out under simulated in vivo sink conditions with constant replacement of the dissolution medium and specific apparatuses and protocols as described by the USP.
- The primary objective of dissolution rate studies is the assessment of oral drug absorption under physiological conditions, and the Biopharmaceutical Classification System (BCS) utilizes 250mL of dissolution fluid.
- Physiological conditions in the gastrointestinal (GI) tract after ingesting 250mL of water are reported, including stomach and intestinal pH levels.
- Factors influencing drug dissolution rate include the diffusion layer thickness, agitation, pH, solubility, and the influence of excipients, surfactants, bile salts, particle size, and solid state properties.
- The thickness of the diffusion layer decreases over time, leading to an increase in the intrinsic dissolution rate, and the dissolution rate depends on the way solid particles are scattered over the bottom of the vessels.
- The pH of the dissolution medium, the solubility and dissolution of weak electrolytes and salts, and the influence of excipients can affect the dissolution rate of drugs.
- Excipients in drug formulations can increase or decrease the aqueous solubility of drugs, with different effects from substances such as lactose, starch, lubricants, and surfactants.
- Bile salts can form micelles, enhancing the solubility of lipophilic drugs and potentially increasing the dissolution rate of poorly water-soluble drugs.
- Particle size and surface area have a direct relationship with the dissolution rate, with micronization of particles increasing the dissolution rate and oral absorption.
Test your knowledge of drug dissolution and factors affecting dissolution rate with this quiz. Explore the key steps involved in drug dissolution from solid dosage forms, the importance of in vitro dissolution testing, and the impact of factors such as pH, solubility, particle size, and excipients on drug dissolution rate. Gain insights into the role of bile salts, surfactants, and the Biopharmaceutical Classification System in assessing oral drug absorption.
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