Physical properties of drugs

Question 1

what is a solution?

Answer 1

single phase

Question 1

what is the definition of a solution?

Answer 1

“a mixture of two or more components that form a homogeneous molecular dispersion”

Question 2

what is a saturated solution?

Answer 2

‘Where the solute is at the limit of its solubility at a defined temp. and pressure’

Question 3

how can a drug solubility be changed?

Answer 3

structure altered

Question 4

what do substituents change to effect solubility of drug?

Answer 4

intermolecular forces
interactions between substituents and water
position of substituents on drug

Question 5

what are the two kinds of substituents?

Answer 5

hydrophilic and hydrophobic

Question 6

why is solubility important?

Answer 6

‘preparation of drugs in solution
drug dissolution to understand how drug behaves in the body
related to diffusion, partitioning, absorption’

Question 7

what are the types of solution?

Answer 7

non-electrolytes (non-ionic)
electrolytes (ionic)

Question 8

what is one way to predict solubility?

Answer 8

polarity

Question 9

what are used to improve solubility of drugs in water?

Answer 9

cosolvents

Question 10

why is cosolvent used?

Answer 10

less polar than water

Question 11

what is water good for?

Answer 11

good solvent for ionic and polar substances

Question 12

what is minerals and benzene good for?

Answer 12

good solvent for water insoluble substances

Question 13

how are poorly soluble weak electrolytes improved in solubility?

Answer 13

cosolvent added which increases the relative solubility of the unionized species
also improves the stability of the drug in solution

Question 14

how is solubility predicted?

Answer 14

‘like dissolved like’
e.g. polar dissolves polar

Question 15

what are weak acids more soluble in?

Answer 15

alkaline solutions

Question 16

what is the equation for solubility for weakly acidic drugs?

Answer 16

slide 1
SOM lecture 11 Physical properties of drugs part 3

Question 17

what do S and So stand for?

Answer 17

S=total solubility at a given pH
So=solubility of unionised drug

Question 18

what are basic drugs more soluble in?

Answer 18

acidic solutions

Question 19

what is equation is used to calculate solubility of weak bases?

Answer 19

slide 2
SOM lecture 11 Physical properties of drugs part 3

Question 20

what are Amphoteric (zwitterionic) drugs?

Answer 20

contain both acid and base groups and are ionised at all pH values

Question 21

what equation is used for pH below isoelectric point?

Answer 21

base equation

Question 22

what equation is used for pH above isoelectric point?

Answer 22

acid

Question 23

draw the graph of Solubility of a weak acid, weak base, and amphoteric compound as a function of pH?

Answer 23

slide 4
SOM lecture 11 Physical properties of drugs part 3

Question 24

what is solubility?

Answer 24

property of molecule that representing dissolution capacity

Question 25

what is dissolution rate of a drug described by?

Answer 25

Whitney-Noyes equation

Question 26

what is diffusion?

Answer 26

tendency of a substance to distribute uniformly over a space

Question 27

what does diffusion include?

Answer 27

mass transfer brought about by random walk and associated with concentration gradient

Question 28

what is the driving force of diffusion?

Answer 28

concentration gradient

Question 29

what happens with dissolved solute?

Answer 29

'molecules passively diffuse from areas of high concentration to areas of low concentrate major role in passive transport of drugs across membranes'

Question 30

what is Fick's first law of diffusion?

Answer 30

slide 4 SOM lecture 11 Physical properties of drugs part 4

Question 31

what is D?

Answer 31

constant depending on temperature, solute

Question 32

conditions to use Flick first law equation?

Answer 32

only for steady-state flux

Question 33

what does a negative flux mean?

Answer 33

decreasing concentration

Question 33

what does a higher gradient mean?

Answer 33

the higher the gradient in Fick's law the faster the rate of diffusion

Question 34

what is partition?

Answer 34

'the distribution of drug between two immiscible phases'

Question 35

how is the partition coefficient defined as?

Answer 35

P= Co/Cw Co= concentration in organic phase Cw=concentration in aqueous phase

Question 36

what is P a measure of?

Answer 36

'relative affinity of the solute for an aqueous and a lipid phase'

Question 37

when does the Partition coefficient apply?

Answer 37

when in dilute solutions

Question 38

when is P constant?

Answer 38

'only if a single molecular species is involved'

Question 39

when is equilibrium obtained?

Answer 39

when solute soluble in both phases