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The Science Of Medicines (PHAR 1021) year 1 > Physical properties of drugs > Flashcards

Physical properties of drugs Flashcards

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1
Q

what is a solution?

A

single phase

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1
Q

what is the definition of a solution?

A

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

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2
Q

what is a saturated solution?

A

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

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3
Q

how can a drug solubility be changed?

A

structure altered

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4
Q

what do substituents change to effect solubility of drug?

A

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

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5
Q

what are the two kinds of substituents?

A

hydrophilic and hydrophobic

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6
Q

why is solubility important?

A

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

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7
Q

what are the types of solution?

A

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

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8
Q

what is one way to predict solubility?

A

polarity

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9
Q

what are used to improve solubility of drugs in water?

A

cosolvents

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10
Q

why is cosolvent used?

A

less polar than water

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11
Q

what is water good for?

A

good solvent for ionic and polar substances

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12
Q

what is minerals and benzene good for?

A

good solvent for water insoluble substances

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13
Q

how are poorly soluble weak electrolytes improved in solubility?

A

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

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14
Q

how is solubility predicted?

A

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

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15
Q

what are weak acids more soluble in?

A

alkaline solutions

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16
Q

what is the equation for solubility for weakly acidic drugs?

A

slide 1
SOM lecture 11 Physical properties of drugs part 3

17
Q

what do S and So stand for?

A

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

18
Q

what are basic drugs more soluble in?

A

acidic solutions

19
Q

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

A

slide 2
SOM lecture 11 Physical properties of drugs part 3

20
Q

what are Amphoteric (zwitterionic) drugs?

A

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

21
Q

what equation is used for pH below isoelectric point?

A

base equation

22
Q

what equation is used for pH above isoelectric point?

A

acid

23
Q

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

A

slide 4
SOM lecture 11 Physical properties of drugs part 3

24
Q

what is solubility?

A

property of molecule that representing dissolution capacity

25
Q

what is dissolution rate of a drug described by?

A

Whitney-Noyes equation

26
Q

what is diffusion?

A

tendency of a substance to distribute uniformly over a space

27
Q

what does diffusion include?

A

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

28
Q

what is the driving force of diffusion?

A

concentration gradient

29
Q

what happens with dissolved solute?

A

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

30
Q

what is Fick’s first law of diffusion?

A

slide 4
SOM lecture 11 Physical properties of drugs part 4

31
Q

what is D?

A

constant depending on temperature, solute

32
Q

conditions to use Flick first law equation?

A

only for steady-state flux

33
Q

what does a negative flux mean?

A

decreasing concentration

33
Q

what does a higher gradient mean?

A

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

34
Q

what is partition?

A

‘the distribution of drug between two immiscible phases’

35
Q

how is the partition coefficient defined as?

A

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

36
Q

what is P a measure of?

A

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

37
Q

when does the Partition coefficient apply?

A

when in dilute solutions

38
Q

when is P constant?

A

‘only if a single molecular species is involved’

39
Q

when is equilibrium obtained?

A

when solute soluble in both phases

40
Q
A

The Science Of Medicines (PHAR 1021) year 1 (20 decks)

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