Dissolution of solids

Question 1

Overview of dissolution steps

Answer 1

• Step 1 - solute molecule leaves particle
• Step 2 - creation of cavity in the solvent
• Step 3 - Solute molecule enters cavity

Question 2

Boundry (h) layer

Answer 2

Saturated and drug molecules remain unless extremely saturated

Question 3

Cs

Answer 3

Saturation solubility concentration of the bounday layer

Question 4

Mass transfer

Answer 4

• Drug molecules move from boundary layer to bulk solvent takes time to enter solution to then be absorbed
• Movement of drug into solution

Question 5

Noyes whitney equation

Answer 5

• dm/dt = k1 A(Cs-C)/h
• Chage in mass
• K1 - dissolution rate constant, A - surface area of undissolved solid drug
• If h gets bigger that rate of dm/dt is lower
• Saturated solubility fixed when conditions are fixed

Question 6

Increase saturation solubility

Answer 6

• Surface area of the undissolved solid drug top of fraction - reduce particle size
• Increase temp increase Cs (endothermic)
• Change solvent add second solvent cosolvent alter Cs
• Viscosity of dissolution medium
• Molecular characteristics size
• Thickness of boundary layer

Question 7

Things that impact thickness of boundary layer

Answer 7

• Agitation of drug in solution in the dissolution medium increase thickness of h
• Cannot be altered in vivo

Question 8

Experiment to determine solubility

Answer 8

• Drug and solvent should be as pure as possible use buffer instead of water to resemble stomach
• Magnetic stirring bar
• Cupboard and controlled chamber temperature e,g, 37 like body
• Has to look cloudy if not add more drug
• Take sample filter it or centrifuge it
• Take supernatant from the solution in the centrifuge
• Use UV spectrometer more drug more absorbance light goes through the solution more absorbance more drug required to saturate solution
• Calibration curve line of best fit assume concentration of drug in solution

Question 9

Dissolution process

Answer 9

• After swallowing tablet the drug molecule enters solution
• Layer surounding the crystal gets saturated called bounday layer
• Drug molecule moves to bulk solvent

Question 10

Concentration of drug in solution at time

Answer 10

• Increase volume of solvent
• Remove dissolved drug from solution

Question 11

Dissolution weight constant

Answer 11

• Effects viscosity of the medium
• Molecular characteristics such as size of molecule