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Ceutics Midterm 2 > Solubility 1/2 > Flashcards

Solubility 1/2 Flashcards

1
Q

Rare Exceptions to solubility

A
  • Chemically “inert” nanoparticals
    • gold
      • Carrier for chemically insoluble drugs
      • Imaging agents
    • silver
      • antimicrobial agent
  • Insoluble Particles
    • Dimensions mimicking rod-shaped bacteria (1x5um)
      • local irritation / tissue dmg when into the lung
      • carcinogen = exposure is chronic
    • Silica/carbon/asbestos
  • **SIZE MATTERS
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2
Q

M-cells

A
  • Specialized cells in GI tract
    • *PHAGOCYTOSIS
    • transport sub-micron size insoluble particles
  • Bypass blood/liver
  • LIMITED CAPACITY
    • ​need enough drug to have efficacy, so typically would not bring in enough.
  • –> enter some infectious agents
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3
Q

Water Solubility is….

A

The key to success delivery of more than 99% of medicines in use.

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4
Q

Supersaturation

A
  • When the soulubility limit is EXCEEDED
    • solulte will spontaneously PRECIPITATE out of solution
  • Not instantaneous
    • persists for a period of time
      • needs a seed –> nucleation
  • Factors that inhibit diffusion (inhibit aggregation
      • viscosity
    • low temperature
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5
Q

Maximum equilibrium solubility

=

A

*Under EQ, 2 process happening at same time

Rate of dissolution of the solute from a suspension of a undissolved particles of the solute in the solution is

=

the rate of precipitation and deposition of solute from the solution BACK onto solid particles of the solute suspended in the solvent

*LARGER PARTICALS => Grow at the expense of smaller paticles due to surface area

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6
Q

Non-electrolyte Solution

A

No ions are formed on dissolution in water

does not increase electrical conductivity of the solution

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7
Q

Electrolyte Solutions

A

Ions are formed upon dissolution in water

increases electrical conductivity

  • Strong
    • Dissociate completely
    • HCl / Na2So4
  • Weak
    • Partial dissociation
    • CO2, phenobarb, ephedrine <2
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8
Q

BCS

Definition of HIGHLY SOLUBLE

A

1 dose (highest available stength)

will dissolve completely in 250ml of water

between ph 1 - 7.5

**dose, not weight (as in USP)

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9
Q

BCS Class 1

A

High Solubility

High Permeability

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10
Q

BCS Class 2

A

LOW SOLUBILITY

High Permeability

*phenytoin

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11
Q

BCS

Class 3

A

High Solubility

LOW PERMEABILITY

cimetidine

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12
Q

BCS

Class 4

A
  • LOW SOLUBILITY*
  • LOW PERMEABILITY*

taxol

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13
Q

Colloidal Dispersions

(nanosuspensions)

A

*NOT SOLUTIONS

Consist of small particles ranging between

1-~500nm

(egg white/jelly/blood plasma)

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14
Q

Coarse Dispersions

A

*NOT SOLUTIONS

Consist of particles LARGER than

~0.5um =

~500nm =

~500 Angstroms

suspensions that need to be shaken / sand&water / RBC in plasma

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15
Q

Forces Affecting Solubility

A
  • Cohesion
    • ​Attraction of like molecules (like dissolves like)
  • Adhesion
    • Attraction of UNLIKE molecules
      • Dipole moments
        • Reduce entropy / impose structure in liquids
      • Ion-dipole iteractions
        • enhance solubility of ionic species in solvents w/ larger dipole moments
      • Hydrogen bonds
        • enhance local structure formation in solvents w/ larger dipole moments
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16
Q

Steps to DISSOLUTION

A
  1. Remove molecule from the crystal lattice (disruption of solid mass)
    1. REQUIRES WORK ++
  2. ​Cavity must be created (HOLE)
    1. ​REQUIRES WORK ++
  3. Dissolving solute molecule Moves into the cavity and interacts with the solvent (INSERTING)
    1. LOSES WORK —
      1. ​-n x work​​

**Dissolution occurs as long as the SUM is <0

17
Q

Indicators of Molecular Cohesion

between solute molecules

A

The Boiling Point of liquids

&

melting point or glass transition of solids

INCREASE Phase transition temp –> DECREASE solubility

18
Q

Hydration of Ions

A

Size and Charge Matter!

may have opposing effects on solubility

19
Q

Hydrophobic Hydration

A

Nonpolar portions of solute molecules have a high structure

INDUCING EFFECT

V

REDUCES the entropy of the solution

**due to water “cage” reduces entropy

20
Q

Common Ion Effect

A

Use of a different salt form

V

Increases the apparent solubility

observed for hcl salts of some weakly basic drugs

21
Q

Salting OUT

A

Adding excipient salts w/ small cations / small anions (NaCl)

to solutions of drugs that dissociate in water to form saltes

—> REDUCE THE SOLUBILITY OF THE DRUG SALT

22
Q

Salting In

A

Addition of excipient salts w/ LARGE cations or Large anions (p-touelenesulfonate)

INCREASE the solubility of drug salt

23
Q

pH = pKa

A

50% of the drug is ionized

so….

Stotal = 2So

Stotal=So+[Concentration of ionized species]

So=solubility of UNIONIZED form

24
Q

Amphoteric Substances

A

Drugs are both weakly basic / acidic

there exist a pH where the net charge is ZERO

= Isoelectric point

@isoelectric point solubiity is MINUMUM

25
Q

Determining pKa

using solubility data

A

*for poorly soluble drugs that are weak acids/bases

you can estimate pKa

When pH is @ 2 x (solubility of unionized form So)

ph = pKa

26
Q

Solubility changes by a Factor of 10 when….

A

*in pH regions where most of the drug is IONIZED…

Changing the pH by 1

–> solubility changes by a factor of 10!

*unless ionized form is exceeded.

***adjusting pH to favor formation of an ionized form is a great way to increase solubility of an ionizable drug

27
Q

Water as a Solvent

A
  • Polar Solvant
  • High dielectric constant = 80
  • ~modest dipole moment =1.84 debye units
  • High hildebrand solubility parameter
    • 23cal1/2cm-3/2, related to solvent’s cohesive e- density
    • measure of how difficult it is to remove a molecule of solvent by vaporization from the bulk solvent
28
Q

Non-Polar Solvents

A
  • Benzane
    • Dielectric constant = 2 & 0 dipole moment
  • Hexane
    • Dielectric constant = 2 & 0 dipole moment
  • CO2
    • Dielectric constant = 1.6 & 0 dipole moment
29
Q

Solvents w/ INTERMEDIATE polarity

A
  • Ethanol / Isopropanol / Acetone
    • miscible with BOTH polar and non-polar solvents
  • have intermediate dielectric constants/dipole moments / hildebrand solubility parameters
  • *used to wash away spills, since it should be able to dissolve most things
30
Q

Aqueous Co-solvents

A
  • Solvents of intermediate polarity
    • ethanol/glycerol/ propylene glycol, polyoxethylene glycos
  • Mixed w/ Water to solubize poorly soluble non-polar drug substances
  • *NONLINEAR / NONIDEAL
    • ​hard to predict the solubility
  • BEWARE OF TOXICITY ISSUES
    • ​percipitation can form
    • Metabolic products of ethylene glycols
      • prefer propylene glycol
31
Q

Complexation

A

Co-solutes that interact w/ poorly soluble solutes form complexes

–>ENHANCES Solubility

of poorly soluble solutes if the complex itself has high h2o solubility

ex. cyclodextrins / serum albumin (acts as a carrier)
* ~slow rate of administration needed to allow for drug to form complex with serum albumin*

32
Q

Shake-flask Method

A

Used to measure Octonal-water partition coefficients

  1. Mix Octanol / Water
  2. Known amount of drug added -> shaken vigorously
  3. Phases are allowed to seperate
    1. Drug is measured in each phase
33
Q

Half-Maximal Partitioning

for Weak Acids (ph~5)

A

50% of maximum partitioning occurs at this pH

pH = pKa + logP (octonal/water)

PLUS

This is how drugs are mostly ionized @ intestines

@pH of 6-7, and are readily absorbed through lipid membranes

34
Q

Half-maximal partitioning

for Weak Bases

A

50% of maximum partitioning occurs at this pH

pH = pKa - logP (octonal/water)

MINUS

35
Q

Maximum Partitioning

for Amphoteric Compounds

A

Maximum partitioning into octonol occurs at

Isoelectric Point

36
Q

Cohesion

A

Attraction of LIKE molecules

LIKE DISSOLVES LIKE

37
Q

Adhesion

A

Attraction of UNLIKE molecules

  • Dipole moments
    • Reduce entropy / impose structure in liquids
  • Ion-dipole iteractions
    • enhance solubility of ionic species in solvents w/ larger dipole moments
  • Hydrogen bonds
    • enhance local structure formation in solvents w/ larger dipole moments
38
Q

Supersaturated Solution

A

Precipitation of excess solute requires a triggering event (NUCLEATION)

When MAXIMUM equilibrium amount of solute is dissolved in a soleunt.

Ceutics Midterm 2 (7 decks)

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