Preformulation - Dissolution

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Questions and Answers

What characterizes the process of dissolution compared to solubility?

Dissolution is static, while solubility is dynamic.

Dissolution is a property of liquids only.

Dissolution refers to the formation of a solid.

Dissolution involves a solid drug becoming dissolved in a solvent. (correct)

What is the definition of melting point (m.p.)?

The average temperature of a substance's phase changes.

The temperature at which a solid transitions into a gas.

The temperature at which a solid changes to a liquid. (correct)

The maximum temperature at which a liquid can remain stable.

What is indicated by the heat of fusion (H)?

The temperature at which a phase change occurs.

The heat absorbed or released during a solid-liquid phase change. (correct)

The mass of solute dissolved in a solvent.

The amount of heat needed for a liquid to become gas.

When considering drug dissolution, which term refers to the mass that dissolves in a solvent at a specific temperature?

Solubility Signup and view all the answers

Which of the following statements is true regarding the process of melting?

Different materials have distinct melting points based on their bond strengths. Signup and view all the answers

What is the primary requirement for drugs in capsules and tablets before absorption can occur?

They must dissolve in the gastrointestinal fluid. Signup and view all the answers

Which step follows after drug disintegration in the dissolution process?

Deaggregation of solid drug particles. Signup and view all the answers

According to Hess's law, what is one of the components needed for the dissolution of a solid in a solvent?

Energy in the form of heat of fusion. Signup and view all the answers

What occurs immediately after a drug is in solution within the blood and tissues?

It begins the absorption process. Signup and view all the answers

What does the dissolution process inherently require?

A combination of the solid with a solvent. Signup and view all the answers

Which is a result of successful drug dissolution in the gastrointestinal environment?

Transfer of dissolved drugs into systemic circulation. Signup and view all the answers

What is the sequence of steps involved in the drug dissolution model illustrated?

Disintegration, deaggregation, dissolution. Signup and view all the answers

What key factor is necessary on the molecular level to facilitate drug dissolution?

Heat energy to break down molecular bonds. Signup and view all the answers

What is required for the process of solvation to occur effectively?

Interaction between solute and solvent Signup and view all the answers

How does the Noyes-Whitney equation relate to drug dissolution?

It describes the rate of drug dissolution based on diffusion. Signup and view all the answers

What does the dissolution rate constant (k) in the Noyes-Whitney equation depend on?

Diffusion properties of the solute Signup and view all the answers

Which of these factors does NOT affect drug dissolution according to the provided information?

Ambient light conditions Signup and view all the answers

In an endothermic dissolution process, which condition is true?

-2UsL < Uss + ULL Signup and view all the answers

What does the variable D represent in the Noyes-Whitney equation?

Diffusion coefficient Signup and view all the answers

The thickness of the diffusion layer (h) plays what role in drug dissolution?

It determines the concentration difference in the solution. Signup and view all the answers

Which statement best describes the term 'solvated entity'?

A discrete structure formed when solvent surrounds solute molecules. Signup and view all the answers

What effect do excipients have in the context of drug dissolution?

They enhance the rate of dissolution. Signup and view all the answers

Which of the following accurately describes a characteristic of exothermic processes in dissolution?

Heat is released when the solute and solvent interact. Signup and view all the answers

What happens during the process of drug dissolution when solute molecules diffuse away?

They become part of the bulk solution. Signup and view all the answers

During the dissolution process, what is one key factor that determines the surface area available for a solid drug?

The crystalline form of the drug Signup and view all the answers

Which variable in the Noyes-Whitney equation is a direct indicator of the concentration in the bulk solution?

CB Signup and view all the answers

Which of the following describes the impact of agitation on drug dissolution?

It improves the rate at which the drug dissolves. Signup and view all the answers

Study Notes

MPharm Programme: Preformulation-Dissolution

Course presented by Prof. Amal Ali Elkordy
Course focuses on preformulation and dissolution aspects of medicines.
Email address for lecturer provided.

Drug Dissolution: Overview

Definitions of key terms are discussed.
Importance of drug dissolution process is explained.
Methods to measure drug dissolution are covered.

Drug Dissolution Principles

States of matter: solid, liquid, and gas
Melting: the process of changing a solid to a liquid through heat
Solubility: the amount of solute dissolving in a given mass or volume of solvent at a specific temperature, a static property
Dissolution: the process by which a solid drug dissolves in a solvent, a dynamic property

Melting

Melting point (m.p.): temperature at which a solid transforms into a liquid.
Melting requires heat; heat of fusion (ΔH) is the amount of heat absorbed or released during a phase change.
Values for ΔH and melting point are provided for aspirin and palmitic acid.

Importance of Drug Dissolution

Most drugs need to dissolve in bodily fluids before absorption.
Drugs in capsules and tablets must dissolve in gastrointestinal fluids for absorption.

Drug Dissolution Process

Drugs in dosage forms undergo disintegration and deaggregation.
This leads to dissolution in the gastrointestinal tract, allowing for absorption into blood and tissues.
Dissolution stages are visualized in a diagram.
The dissolution process involves enthalpy change (ΔH).

Illustration of Drug Dissolution Process: Molecular Level

Dissolution involves breaking bonds within the solid drug.
Bonds are formed between solute and solvent.
This process is either endothermic or exothermic, depending on the relative energies involved.
Step-by-step illustrations details the mechanisms, including dissolving solid, solute-solvent interaction and heat of fusion for solute and solution.

Illustration of Drug Dissolution Process: Simple Diffusion Model

Simple diffusion model demonstrates the process.
An illustration shows the diffusion layer, solid drug, aqueous phase, and concentration gradients.

The Noyes-Whitney Equation

This equation describes drug dissolution based on simple diffusion (film theory).
The equation relates the dissolution rate (dC/dt) to various factors including: dissolution rate constant (k), surface area (A), the saturation solubility (Cs), and concentration in the bulk solution (Cb).

Noyes-Whitney Equation (Continued)

The equation accounts for factors like diffusion coefficient (D), and thickness of the diffusion layer (h).
The equation is used for estimating and predicting dissolution rates for pharmaceutical particles.
"Sink" conditions are encountered when rate of absorption is faster than the rate of dissolution.

Factors Affecting Drug Dissolution

Agitation of dissolution medium affects the diffusion layer thickness.
Viscosity of the solution impacts diffusion coefficient.
Particle properties, including size, wetting, porosity, and surface area affect the process.
Crystalline form and saturation solubility (Cs) of the drug are crucial factors impacting the dissolution rate.
Volume of solution affects the drug concentration in the bulk (Cb).
Excipients in the formulation affect the process.

Methods for Measuring Drug Dissolution

Different methods for measuring drug dissolution are described.
- Beaker method
- Flask stirrer method
- Rotating basket method
- Paddle method
- Flow-through-cell (for low solubility drugs)
Figures depicting these methods are also included.

Dissolution Testing and Sink Conditions

Sink conditions (Cb << Cs) are ideal for dissolution studies.
Non-sink conditions (CB approaches Cs ) require more complex analysis.
Steps for setting up dissolution testing are detailed. This includes determining saturation solubility (Cs), withdrawing samples at intervals, and measuring drug concentration in samples to make a dissolution curve, plotting concentration vs. time.

Dissolution Curve

Results are displayed as percentage of the dissolved drug plotted against time.

Effect of Particle Size on Drug Dissolution

Smaller particles dissolve faster than larger particles.
The rate of drug dissolution increases significantly with smaller particle size, important for better dissolution and absorption in the body.

Influence of Wetting on Drug Dissolution

An example illustrates how wetting a drug (hydrophobic drug example: cinnarizine) can impact its rate of dissolution in different aqueous solutions.
Better wetting facilitates faster dissolution.

Utilisation of Polymorphism to Improve Drug Solubility

Metastable polymorphs can dissolve faster than stable polymorphs, enhancing solubility.
Example graph showing how metastable polymorphs dissolve over time.

Summary of the Course

Simple models illustrate drug dissolution processes via diffusion.
The Noyes-Whitney equation explains dissolution rates based on particle properties and experimental conditions.
"Sink conditions" and their importance in drug dissolution studies are explained.
Common dissolution methods are described.

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Description

This quiz covers essential aspects of preformulation and dissolution in pharmaceuticals, focusing on the definitions, principles, and methods used in drug dissolution. You will explore the states of matter, melting points, and the dynamics of solubility. Perfect for MPharm students looking to enhance their understanding in this field.