Solutions 2

• What does the rate of dissolution depend on?

  Agitation, particle size, viscosity, pH, temperature
• What is the Intrinsic Dissolution Rate (IDR)?

  Measure of dissolution independent of variables
• What conditions are kept constant to measure IDR?

  Surface area, agitation, pH, ionic strength
• What does the equation for IDR represent?

  Rate of mass transfer per area of dissolving surface

  
• How can the IDR equation be simplified?

  By introducing the intrinsic dissolution rate constant, k
• What are the units of the intrinsic dissolution rate constant, k?

  cm/s
• How do you calculate the intrinsic dissolution rate constant, k?

  Using the formula with mass, time, and area
• What indicates that sink conditions apply in Example 1?

  Concentration is less than 10% of saturated solubility
• What is the intrinsic dissolution rate constant, k, in Example 1?

  2.38 x 10^-4 cm/s
• How do you calculate the diffusion coefficient in Example 1?

  By multiplying k by the boundary layer thickness
• What is the diffusion coefficient in Example 1?

  1.19 x 10^-6 cm²/s
• What is the total surface area of the granules in Example 2?

  0.14 m²
• What indicates that sink conditions apply in Example 2?

  Concentration is less than 10% of saturated solubility
• What is the diffusion coefficient in Example 2?

  2.23 x 10^-7 cm²/s
• Why measure the Intrinsic Dissolution Rate (IDR)?

  • To depict the dissolution rate of a drug
  • To screen drug candidates and understand solution behavior
  • To determine batch-to-batch chemical equivalency

  
• What does the Noyes-Whitney equation assume?

  Constant surface area during dissolution
• What is the Hixson-Crowell Cube Root Law based on?

  Uniformly-sized particles and cube root of weight
• What does the plot of cube root mass undissolved against time yield?

  A linear plot with intercept and gradient

  
• What is the cube root dissolution rate constant, k, in Example 3?

  0.0158 g^1/3 min^-1
• What is the intrinsic dissolution rate (IDR)?

  Measure of dissolution independent of variables
• What should the cube of the intercept equal in Example 3?

  Approximately 0.5 g

  
• What is the significance of the intercept in Example 3?

  • Represents the initial mass (M₀)
  • Should be approximately equal to the initial mass

  
• What factors affect the rate of dissolution?

  Agitation, particle size, viscosity, pH, temperature
• What conditions must be constant to measure IDR?

  Surface area, agitation, pH, ionic strength
• What does the equation for IDR represent?

  Rate of mass transfer per area of dissolving surface

  
• What is the unit of the intrinsic dissolution rate constant, k?

  cm/s
• How do you calculate the intrinsic dissolution rate constant, k?

  Using the modified equation with known values
• What indicates that sink conditions apply in a dissolution test?

  C is less than 10% of Cs
• What is the intrinsic dissolution rate constant, k, for the given example?

  k = $2.38 \times 10^{-4} \text{ cm s}^{-1}$
• How do you calculate the diffusion coefficient, D?

  D = k x h
• What is the diffusion coefficient for the given example?

  D = $1.19 \times 10^{-6} \text{ cm}^2 \text{ s}^{-1}$
• What is the total surface area of the granules in Example 2?

  A = $0.14 \text{ m}^2$
• What is the intrinsic dissolution rate constant for Example 2?

  k = $2.23 \times 10^{-5} \text{ cm s}^{-1}$
• How do you determine if sink conditions apply in Example 2?

  C is less than 10% of Cs
• What is the Hixson-Crowell Cube Root Law used for?

  To describe dissolution with changing surface area
• What does the Hixson-Crowell Cube Root Law assume about drug particles?

  Particles are uniformly sized
• What does the plot of cube root mass undissolved against time yield?

  A linear plot

  
• What is the cube root dissolution rate constant, k, in Example 3?

  k = $0.0158 \text{ g}^{1/3} \text{ min}^{-1}$
• How is the intercept of the plot related to the initial mass?

  It gives the value of M0
• What should the cube of the intercept approximate in Example 3?

  Approximately 0.5 g