Lecture 01, 2

• What is the Noyes-Whitney equation used for?

  To describe drug dissolution rates

  
• What factors affect the dissolution of a drug?

  • Surface area of the drug
  • Temperature of the solvent
  • Solvent composition
  • Agitation or stirring
• What are key parameters for in vitro dissolution testing?

  Volume, pH, temperature, apparatus speed
• How is solubility defined?

  Amount of substance that dissolves in a solvent
• What are the key differences between solubility types?

  Types include thermodynamic and kinetic solubility
• What factors affect the solubility of a solid in an aqueous medium?

  • Temperature
  • pH of the solvent
  • Molecular structure
  • Presence of co-solvents
• What is dissolution?

  Process of solid substances forming a solution
• What is the rate of dissolution?

  Amount of drug dissolving per unit time
• What is the dissolution theory based on the diffusion layer model?

  • Stage 1: Interfacial reaction
  • Stage 2: Diffusion through the boundary layer
• What happens to energy during dissolution?

  Energy is absorbed or released during bond changes
• What are the types of dissolution rates of solids in liquids?

  • Interface-controlled
  • Diffusion-controlled
• What is the relationship between diffusion layer thickness and dissolution rate?

  Inverse relationship; thicker layer slows dissolution
• What is the intrinsic dissolution rate (IDR)?

  Characterises dissolution and apparent solubility
• What are typical parameters for dissolution testing?

  • Volume: 900 mL
  • pH: 1.2 to 6.8
  • Temperature: 37 ± 0.5 °C
  • Apparatus speed: 50/100 rpm
• What is considered a rapidly dissolving product?

  ≥75% of labelled dose dissolved in 45 min
• How does particle size affect dissolution rate?

  • Smaller particles increase surface area
  • Increased surface area enhances dissolution rate
• What role do surfactants play in dissolution?

  They improve wettability and dissolution rates
• What is the maximum amount of solute in solubility?

  Most stable crystalline form in solution
• What are the expressions of solubility?

  • Descriptive solubility (USP, BP, PhEur)
  • Units: µg/mL, mg/mL, g/mL, g/L, kg/L
• What is thermodynamic solubility?

  Equilibrium concentration profile of solute
• What is kinetic solubility?

  Concentration-time profile of solute dissolution
• What are the precautions for solubility measurement?

  • Use pure solvent and solute
  • Test after saturation
  • Reliable analytical methods
  • Controlled temperature
• What are the challenges in thermodynamic solubility measurement?

  • Number of compounds assessed
  • Scarcity of compounds
  • Questionable purity
  • Crystallinity of early discovery lots
• What factors affect solubility based on structural features?

  Molecular surface area, melting and boiling points
• How does molecular surface area affect solubility?

  • Larger molecules require more solute-solvent contacts
  • Solubility decreases with increased molecular surface area
• How do melting and boiling points relate to solubility?

  Higher points generally decrease aqueous solubility
• What is polymorphism in relation to solubility?

  • Different structural forms of the same compound
  • Varying solubility, stability, and bioavailability
• How does temperature affect solubility?

  Increased temperature usually increases solubility
• What is the role of co-solvents in solubility?

  Increase polarity and enhance solubility
• How does pH influence solubility?

  It affects the degree of ionisation of drugs
• What parameters determine solubility in relation to pH?

  • Degree of ionisation
  • Molecular size
  • Interactions with solvent
  • Crystal properties