2.) Pharmaceutical Formulations 1

DISSOLUTION
1. What is dissolution?
  1. Dissolution is the movement of molecules or ions from a solid state to a solution state
  2. Solubility on the other hand is the amount of solute that dissolves in a solvent
2. Why is dissolution important?
  1. Many drugs are in the form of solutions
  2. Drugs must be in solution to be absorbed across biological membranes
  3. Drugs of low solubility provide bioavailability challenges
3. Process
  1. The first thing is the removal of the solute molecule from the solid
  2. Second the solvent molecules create a cavity
  3. The individual solute molecules fit inside these cavities
4. Energy Change
  1. Necessary to overcome cohesive forces (Wa +Wb)
    1. Replaced by adhesive forces
  2. An Ideal solution has an energy change of zero.
5. Noyes Whitney Equation
  1. How is it used?
    1. The Noyes Whitney equation is used to calculate the rate of dissolution i.e the rate at which a molecules in a solid state move into a solution phase
  2. The Noyes Whitney equations simply states that the diffusion co-efficient, the surface area of the solute particles, the concentration of the solute particles at the boundary layer and the height of the boundary layer all effect the rate of dissolution
    1. The diffusion co-effeicient, the SA od the solute particles and the the concentration of solute particles at the boundary layer are all directly proportional to the rate of dissolution
    2. Whereas the height of the boundary layer is inversely proportional to the rate of dissolution
  3. Dissolution Mechanism
    1. Overall the rate of dissolution depends on the rate determining step, this is the diffusion of the solute molecules across the static boundary layer
  4. Sink Conditions
    1. If c is less than 10% of Cs then sink conditions apply
  5. Assumptions
    1. The Noyes Whitney equation assumes that there is no change in the surface area of the dissolving particles. Therefore if a change of surface area occurs it cannot be used
SOLUTIONS
1. What is a solution?
  1. A mixture of two or more components to form a single. molecularly homogeneous phase
  2. In pharmacy we are interested in how a solid or liquid mixed within another liquid
2. What are the advantages and disadvantages?
  1. Advantages
    1. Easy to swallow
    2. Rapid Absorption
    3. Onset of action faster
    4. Can be flavoured
  2. Disadvantages
    1. Hard to transport
    2. Less stable than solid dosage forms
    3. Can be easily contaminated
    4. Dependant on patients ability
    5. Can require taste masking
3. Choice of Solvent
  1. Aqueous
  2. Non- Aqueous
4. Types of Solutions
  1. Local Use
  2. Systematic Use
  3. Intermediate Products

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2.) Pharmaceutical Formulations 1

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