Mark Hewitt Flashcards
Make a list of physical and chemical properties of a drug substance that affect their pharmacological activity?
Melting and boiling point Volatility Particle size and shape pH Log P
What is a true solution?
A mixture of 2 or more components that form a homogeneous mixture (one phase)
What types of solutes are possible?
Electrolyte
Non-electrolyte
What is a saturated solution?
The solute is in equilibrium with the solid phase
What is an unsaturated solutions?
Dissolved solute is in a concentration below that necessary for complete saturation
What is a supersaturated solution?
Contains more of the solute than is normal
What are the possible units for solubility?
mol/L
mg/L
ppm
Why is solubility important in pharmaceutics?
As many formulations are solutions, and the drug needs to be dissolved before it can be absorbed
What is intrinsic solubility?
Solubility of the free unionised solute
How can you measure solubility?
Experimentally: Saturated shake flask method and automated Potentiometric acid/base titration
Computationally
Rank in order of solubility:- NaCl, Nicotine, Pentanol, Ethanol, Glucose and Aspirin
NaCl, Ethanol, Glucose, Pentanol, Aspirin and Nicotine
Name the factors that influence solubility?
Number of polar groups (OH) Number of non-polar groups (CH3) If hydrogen bonding can occur Acid/basic characteristics If branched or unbranched Molecular size
What is the partition coefficient (P)?
Ratio of concentration between two immiscible phases
Why is octanol used as a solvent when measuring log P?
As it mimics phospholipids (membrane)
What methods can you use to determine log P?
Shake flask method - need to use octanol and water - don’t need to know structure
HPLC - need to know structure
Electrochemical method - ionisable drugs
Can you determine log P without doing any experiments?
Yes, software package called EPI
Log P increases when?
Increase in size
Increase in carbon atoms - non-polar content
High log P value means?
Less soluble in water - hydrophobic
Less polarising
Low log P value means?
More water soluble - hydrophilic
More polarising
What does a big log P value mean for the delivery of the drug?
Accumulate in the hydrophobic region of the cell membrane, wont get to target
What does a low log P value mean for the delivery of the drug?
Pass through the cell membrane readily but will also pass out of cell membrane readily
What is molality?
Amount of substance (in moles) per unit mass of solvent
What are the units of molality?
mol kg-1
What is Raoult’s law?
The partial vapour pressure of a substance in a mixture is proportional to its mole fraction and its vapour pressure when pure
What is Henry’s law?
The vapour pressure of a volatile solute is proportional to its mole fraction in a solution
What is an ideal dilute solution?
A solution which has a low concentration of solute, so obeys Henry’s law
What is a colligative property of a solution?
That a solute in solution will affect the properties of the solution
List three colligative properties?
Raise in boiling point
Reduction in melting point
Produce an osmotic effect
What are the units for colligative properties?
mol kg-1 = same as molality
What is osmotic pressure?
The pressure that must be applied to the solution to stop the osmotic flow
What is tonicity?
The measure of the osmotic pressure gradient of two solutions separated by a semi permeable membrane
What happens when something is hypotonic?
Draws water in as it has a high solute concentration
What happens when something is hypertonic?
Draw water out as it has a low solute concentration
Tonicity of the plasma?
275-295 mosmol-1
Name a company that produces osmotic pumps commercially?
Alzet
What is the azeotropic point?
Point at which two liquids can not be separated by distillation
Give examples of high azeotropes?
Chloroform/acetone
Nitric acid/water
HCl/water
Give examples of low azeotropes?
Dioxane/water
Ethanol/water
What is the eutectic point?
the lowest temperature for the existence of the liquid phase in a solution
Name three dosage forms that rely on eutectic points?
Suppository
Pessary
Skin patches
What is an incongruent melting point?
Melting point that is lower than expected
what is a plane of symmetry in a crystal?
Divides crystal into two parts that are mirror images of one another
What is an axis of symmetry in a crystal?
A line about which the crystal can be rotated
What is a centre of symmetry in a crystal?
Centre of which the crystal can rotate
