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Drug Solubility Flashcards

(62 cards)

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1
Q

definition of solution

A

dispersion formed by two or more compounds which form a homogenous system

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2
Q

definition of solvent

A

component that determines the phase of the solution - usually the largest proportion

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3
Q

definitions of solutes

A

other components of the solution and are dispersed as molecules or ions throughout the solvent

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4
Q

definition of saturated solution

A

solute is in equilibrium with solute

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5
Q

definition of solubility

A

concentration of a solute in saturated solution at a certain temperature that dissolves to form a homogenous phase

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6
Q

definition of unsaturates/subsaturated solution

A

the dissolved solute is in concentration below that necessary for complete saturation at a definite temperature

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7
Q

definition of supersaturated solution

A

contains more dissolved solute than normal

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8
Q

semi quantative expressions of solubility

A 
very soluble (<1part)
freely soluble (1-10 parts)
soluble (10-30 parts)
sparingly soluble (30-100 parts)
slightly soluble (100-1000 parts)
very slightly soluble (1000-10000 parts)
insoluble (>10000 parts)
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9
Q

quantative expressions of solubility

A 
molarity
% w/w
% w/v
mg/ml
g/100ml
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10
Q

what is a diffusion layer

A

when molecules in surface layer of drug dissolve to form a saturated solution around particles
dissolved drug molecules pass through dissolving fluid to contact absorbing mucosa
replenishment of diffusing layer by further drug dissolution

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11
Q

Factors affecting dissolution rate

A 
surface area of undissolved particles
solubility in dissolution medium
conc in bulk of solution
diffusion coefficient
thickness of boundary layer
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12
Q

Reduction in particle size

A

inclreases dissolution rate - exposure of increasing amounts of solute to the solvent
solubility increased with decreasing particle size

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13
Q

to increase solubility

A

salt form of drug used

aqueous solubility can be reduced by esterification of prent drug

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14
Q

effect of esterification

A

masks the taste and protects from degredation in GI

can facilitate absorption in GI tract

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15
Q

polymorphism

A

crystallisation conditions -> molecules/ions arrange differently in lattice -> stable polymorph (less soluble) or metastable polymorph (more soluble, less stabe)

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16
Q

counterions used in salt formations

A

HCl, sulphate, mesylate, phosphate, maleate, salicylate, tartrate, lactate, citrate, succinate, acetate, sodium, potassium, calcium, lithium, magnesium, inc, choline, aluminium

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17
Q

weak bases in GI tract

A

high dissolution rate in stomach

dissolution rate falls as pH of GI tract rises

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18
Q

weak acids in GI tract

A

minimal dissolution in the stomach

dissolution rate increases down the gut

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19
Q

salt dissolution

A

dissolution of the salt form is greater than the free form

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20
Q

effect on use of salt form

A

modifies pH of diffusion layer
salt of weak acid increases pH of diffusion layer
salt of weak base decreases pH of diffusion layer
salt is preferable to acid as dissolution is better controlled
salt form controls pH of diffusion layer indepentdly of position of GI tract, this improves dissolution rates

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21
Q

co-solvent advantage

A

increases solubility

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22
Q

when does precipitation occur

A

when pH of solution is adjusted to produce mostly unionised molecules, exceeding solubility of their form

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23
Q

how to improve solubility of weak electrolytes or non-polar compounds

A

adding water-miscible solvents in which the compound is soluble

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24
Q

what are co-solvents

A

vehicles used in combination with water to increase solubility
the solubility in mixed systems is greater than that of individual solvents

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25
Cosolvency
obtains aqueous-based systems in which the drug solubility is higher than aqueous solubility; it formulates higher concentrations of the drug it improves stability of formulation
26
cosolvents
organic compounds miscible with water better solvents than water for a drug(H-bond acceptors/donors, small hydrocarbon regions) most cosolvents are liquids (ethanol, glycerol, propylene glycol) some are solids that are highly soluble in water (urea, PEG, PVP)
27
effect of cosolvents decreasing H-bond density of aqueous systems
reduces cohesive interactions of water, which reduces polarity of solutions, so the solution is less effective than water in squeezing out nonpolar structures solubilisation by cosolvency
28
cosolvency
water-ethanol has more cosolvency than water-glycerin with non-polar drugs cosolvents increase solubility of non-polar and semipolar solute in water as solutes become more polar, cosolvency becomes less efficient; it will decrease solubility of a polar solute in water
29
what are cyclodextrins
inclusion compounds that enhance solubility of drugs that are poorly soluble in water they are enzymatically modified starches with a ring of glycopyranase units the centre of the ring accommodates lipophilic molecules (outer ring is hydrophlic and inner is non-polar)
30
what are surfactants
surface active agents that enhance solubility
31
what do cyclodextrins do
they incorporate the non-polar portion of one polar molecule into the non-polar cavity of another molecule or group of molecules that is water soluble driving force is similar to micellar solubilisation - it reduces the non-polar water interfacial area by inserting the solute into the complexing agent the complex formed increases solubility initially but decrease in solubility as drug is released
32
beta cyclodextrins
useful solubilisers used in the controlled release of drugs
33
use of surfactants
have the ability to reduce surface tension at an interface without requiring large concentrations lower conc required = better surfactant highest reduction of interfacial tension obtained with solutes that combine in their molecular structure, one element having a high afinity for the solvent and one having minimal affinity for a solvent
34
role of surfactants
resolves interfacial tension between two immiscible liquids | more surface tension = less thermodynamically stable
35
structure of surfactants
polar head group and lipophilic/non-polar chain | can be presented in different proportions, which determines the surfactant solubility in water or oil
36
what is HLB
hydrophile/lipophile balance
37
solutions of surfactants
unusual properties at dilute solutions act as normal solutes and normal electrolytes amiphiles exist separately and are of such a size to be sub-colloidal as concentrated solutions, they aggregate to form a micelle
38
what is critical micelle concentration
the narrow concentration range which causes surfactants to aggregate to form a micelle
39
what is micellisation
alternative mechanism to adsorption permits strong water-water interations that would be prevented if the surfactant molecules were in solution as single molecules (hydrophobic effect)
40
physical properties that change with CMC
osmotic pressure, tubidity, electrical conductivity, surface tension CMC can increase with increase of polarity of surfactant head group CMC can decrease with temp, pH, additional surfactants or electrolytes
41
what is Kraft point
temp/time where solubility is equal to CMC when kraft point is larger than temperature, the CMC is larger than solubility and micelles cannot form when temp is larger than kraft point, the surfactant forms micelles (self solubilisation)
42
what is the cloud point
for non-ionic surfactants increase in temp causes dehydration of POE chains, decreased solubility, formation of large micelles so the solution becomes cloudy
43
reversing cloudiness of non-ionic surfactants
by cooling | this forms small micelles - called clarification
44
what is critical micelle pH
ionised form of a compound is surface active and unionised form is surface inactive (or has lower CMC than ionised form), a change in pH can cause micellisation
45
geometric properties of micelles
at high conc of surfactants, high viscosity systems may occur cylindrical rods, flattened discs, liquid crystals lamella phase bilayers vesicles
46
groups on non-ionic surfactants
hydroxy ether less polar than ioninsed groups
47
what is a POE number
number of monomeric polyoxyethylene groups in the molecule
48
polyoxyethylene
chains with 20+ ether groups linked to non-polar moiety | several chains then linked to cyclic sugar and alkyl group
49
surfactant applications
anionic: cheap, toxic so only used externally cationic: disinfectant/preservatice properties, o/w emulsifiers nonionic: o/w, w/o emulsifiers, low toxicity and low irritancy, parenteral use
50
parenteral applicaitons for ionic surfactants
haemolysis of RBC and desrtuction of T-cells
51
parenteral applications for non-ionic surfactants
phospholipids, polysorbates, cremophor EL anaphylactic shock, toxicity related to ethylene oxide
52
what is solubilisation
process by which water=-insoluble or patially soluble substances are brought into aqueous solution by incorporation into micelles
53
solubilisation with micelles
site of solubilisation depends on chemical nature of solubilisate more polar solute, more likely to be solubilised closer to the surface polar region of non-ioninc micelle larger than polar region of ioninc micelle
54
what is solubilisation capacity
quantifies solubilisation measure the ability of a surfactant to solubilise a solute molar solubilisation capacity (k)is the number of moles of solute that can be solubilised by one mole of micellar surfactant
55
to decrease CMC
increase hydrocarbon chain length introduce polar region on molecule or double bond branched surfactants will produce smaller micelles
56
semipolar solutes
surface and palisade region largely unaffected by nonpolar region
57
factors of surfactant selection
amount of surfactant required ability to solubilise a solute increased chain length for reduced CMC and reduced solubility
58
Lundelieu's rule
any factors that decreases solubility of surfactant promotes surface activity
59
HLB values
higher HLB = more hydrophilic 100% lipophilic = HLB1 100% hydrophilic = HLB20
60
what is phase intervention temperature (PIT)
HLB varies with temp because relative solubilities of lipophile and hydrophile parts vary with temperature this is more pronounced with non-ionic surfactants becuase their solubility depends on H-bonding
61
temperature on H-bonding
higher temps weaken H-bonds and emulsifiers are less soluble in water common non-ionic emulsifiers are water soluble at low temps to stabalise o/w emulsions oil soluble at high temps to stabalise w/o emulsions
62
PIT of emulsifier
temp at which it changes from o/w to w/o | hydrophilic and lipophilic nature balance

GI (21 decks)

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