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2.) Pharmaceutical Formulations 1
- DISSOLUTION
- What is dissolution?
- Dissolution is the movement of molecules or
ions from a solid state to a solution state
- Solubility on the other hand is the amount
of solute that dissolves in a solvent
- Dissolution is the movement of molecules or
ions from a solid state to a solution state
- Why is dissolution important?
- Many drugs are in the
form of solutions
- Drugs must be in solution to be
absorbed across biological
membranes
- Drugs of low solubility provide
bioavailability challenges
- Many drugs are in the
form of solutions
- Process
- The first thing is the
removal of the solute
molecule from the
solid
- Second the solvent
molecules create a cavity
- The individual solute
molecules fit inside these
cavities
- The first thing is the
removal of the solute
molecule from the
solid
- Energy Change
- Necessary to overcome
cohesive forces (Wa +Wb)
- Replaced by adhesive forces
- Replaced by adhesive forces
- An Ideal solution has an
energy change of zero.
- Necessary to overcome
cohesive forces (Wa +Wb)
- Noyes Whitney Equation
- How is it used?
- 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
- 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
- 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
- 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
- Whereas the height of the boundary
layer is inversely proportional to the
rate of dissolution
- 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
- Dissolution Mechanism
- Overall the rate of dissolution depends on the
rate determining step, this is the diffusion of
the solute molecules across the static
boundary layer
- Overall the rate of dissolution depends on the
rate determining step, this is the diffusion of
the solute molecules across the static
boundary layer
- Sink Conditions
- If c is less than 10% of Cs
then sink conditions apply
- If c is less than 10% of Cs
then sink conditions apply
- Assumptions
- 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
- 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
- How is it used?
- What is dissolution?
- SOLUTIONS
- What is a solution?
- A mixture of two or more
components to form a single.
molecularly homogeneous phase
- In pharmacy we are interested in
how a solid or liquid mixed within
another liquid
- A mixture of two or more
components to form a single.
molecularly homogeneous phase
- What are the advantages
and disadvantages?
- Advantages
- Easy to swallow
- Rapid Absorption
- Onset of action
faster
- Can be
flavoured
- Easy to swallow
- Disadvantages
- Hard to transport
- Less stable than
solid dosage forms
- Can be easily
contaminated
- Dependant on
patients ability
- Can require taste
masking
- Hard to transport
- Advantages
- Choice of Solvent
- Aqueous
- Non- Aqueous
- Aqueous
- Types of Solutions
- Local Use
- Systematic Use
- Intermediate Products
- Local Use
- What is a solution?
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