Mark Hewitt Flashcards
(44 cards)
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
