Physicochemical properties of drugs Flashcards
What are physicochemical properties?
Fundamental characteristics of drugs that influence their behavior in formulations and biological systems.
Why are physicochemical properties important in pharmacy?
They affect drug formulation, solubility, bioavailability, membrane permeability, and clinical effectiveness.
Name five physicochemical properties of drugs.
Molecular weight, solubility, boiling/melting point, partition coefficient (log P), and particle size.
What is the partition coefficient (log P)?
A measure of a drug’s lipid solubility, influencing membrane permeability.
Define solubility.
The maximum amount of solute that can dissolve in a solvent under specific conditions.
What is dissolution?
The process by which a solid drug dissolves in a solvent.
What factors affect solubility?
Lipophilicity (log P), molecular size, pKa, crystal lattice energy, and solvent properties.
How does molecular size affect solubility?
Larger molecules require larger solvent cavities, decreasing solubility.
How much water is required to dissolve a very soluble substance?
<1 mL.
What is the difference between “slightly soluble” and “practically insoluble”?
Slightly soluble requires 100-1000 mL of water, while practically insoluble requires >10,000 mL.
What is the difference between crystalline and amorphous solids?
Crystalline has an ordered molecular structure and sharp melting point, while amorphous lacks order and is generally more soluble.
Why are amorphous forms preferred in pharmacy?
They have higher solubility and dissolve more easily
What is polymorphism in drugs?
The existence of different crystalline forms of the same drug, affecting solubility and stability.
What is the difference between enantiotropic and monotropic polymorphs?
Enantiotropic can convert between forms under different conditions, while monotropic has one stable form.
Why are metastable polymorphs often preferred?
They dissolve faster and have higher bioavailability.
What are crystal hydrates?
Crystalline drugs that incorporate water molecules.
How do hydrates compare to anhydrous forms in solubility?
Hydrates have lower solubility and higher melting points.
Which is more soluble: monohydrate or anhydrous drug?
Anhydrous.
What is crystal lattice energy?
The energy required to separate molecules or ions from a solid crystal.
How does lattice energy affect solubility?
Higher lattice energy means lower solubility.
What factors influence drug dissolution rate?
Wettability, particle size, porosity, solvent properties, and excipients.
How does particle size affect dissolution?
Smaller particles increase surface area, enhancing dissolution rate.
What role do surfactants play in dissolution?
They reduce surface tension and improve wettability.
What does the Noyes-Whitney equation describe?
The rate at which a drug dissolves.
What happens when the diffusion layer thickness decreases?
Dissolution rate increases.
What is the key difference between solubility and dissolution rate?
Solubility is the maximum concentration a solute can achieve in a solvent, while dissolution rate is how fast it dissolves.
Can a drug be highly soluble but dissolve slowly?
Yes, like hydroxypropyl methylcellulose, which dissolves slowly despite high solubility.
What are sink conditions in dissolution testing?
The dissolution medium must be at least 3 times the volume needed for saturation to ensure continued dissolution.
Why are sink conditions important?
They prevent saturation and allow accurate measurement of dissolution rates.
What is diffusion in drug absorption?
The movement of drug molecules from high to low concentration, essential for crossing biological membranes.
Why must a drug be in solution to be absorbed?
Only dissolved molecules or ions can diffuse across membranes.
Higher solubility leads to
better bioavailability
Metastable polymorphs
dissolve faster.
Anhydrous forms
dissolve better than hydrates
Smaller particles
faster dissolution
Sink conditions prevent
dissolution stopping due to saturation
