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Medicines design II - solid dosage forms > L9 Dissolution > Flashcards

L9 Dissolution Flashcards

0
Q

What aspects if the drug formulation can be improved to improve absorption?

A

We cannot change solubility or permeability but we can change dissolution/release rate.

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1
Q

Oral drug adsorption depends on 3

A

Release of drug from dosage from (dissolution)
Solubility
Permiablity across the GI tract

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2
Q

What BA class of molecule gets a biowaiver?

A

Class I
High permeability,
High solubility

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3
Q

Three biopharmacuetical hurdles

A

soulbitlity
GI stability
Permeability

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4
Q

Scientific framework for classifying drug molecules

A

Biopharmacuetical classification system

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5
Q

Is it easier to increase solubility or permeability?

A

Solubility

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6
Q

To increase solubitliy…

A

Change the lattice energy of a crystal so you require less energy to break lattice

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7
Q

Class I

A

High sol high perm

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8
Q

Class II

A

Low sol high perm

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9
Q

Class III

A

High solubility low perm

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10
Q

Class IV

A

Low sol low perms

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11
Q

Pharma use BPC to

A

To justify biowaivers

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12
Q

What is usually step one in trying to improve drug delivery?

A

Reduce particle size. Increase surface area.

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13
Q

If you have something really insoluble what can you do?

A

Nano particles, amorphous form, oily solution

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14
Q

Problems with reducing particle size of a crystal?

A

If a drug decides it wants to be a crystal it will. Do you want to risk it? If it crystallises you get a subtheraputic dose. Therefore it’s never really done.

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15
Q

Two actions of surfactants

A

Aid dissolution and prevent aggregation

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16
Q

Nano particles are a problem becuase

A

They easily agglomerate and act like one massive particle

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17
Q

Options for improving class III 3

A

Mucoadhesives,
Absorption enhancing excipients
Efflux inhibitors

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18
Q

Options for improving class IV 2

A

Liquid filling capsules with absorptions enhancing excipients

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19
Q 
Options to improve class II
5
A

Select more soluble salt/polymorph
Nano particles
Liquid filled capsules (oily self emulsifying vehicles)
Solid dispersions
Addition of surfactants to solid dosage form.

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20
Q

Class I allows biowaiver for

A

Bioavailiblity and bioequivilenace studies

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21
Q

During dissolution drug molecules form

A

surface layer dissolves to form a saturated solution - diffusion boundary layer

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22
Q

How is a concentration gradient form?

A

Dissolved drug molecules with in the boundary layer form concentration gradient with surrounding fluid.

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23
Q

Rate of mass transport when a drug dissolves is dependent on… 2

A

Concentration gradient and diffusion coefficient (flicks law)

24
Q

Replenishment of drug molecules in the diffusion layer is dependent on …

A

Rate of diffusion - the whole process is cycli

25
Q

Cycle of something dissolving

A

Formation of saturated boundary layer around particles, dissolved drug molecules diffuse down concentration gradient into bulk solution, replenished by dissolution of more particles in boundary layer. Cyclic

26
Q

Dissolution is dependent on rate

A

Or diffusion of dissolved molecules from sat boundary layer to bulk

27
Q

Quantitative description of diffusion of dissolved solute across the boundary layer….

A

Noyes-Whitney equation

28
Q

Noyes Whitney equation is

A

-dm/dt= kA (Cs-Ct)

29
Q

Define all parameters of the Noyes-Whitney equation

A 
m Mass of solute passed into solution in time t
dm/dt Rate of dissolution
A Surface area of undissolved solid
Cs Saturation concentration of solute
Ct Concentration at time t
k Intrinsic dissolution rate constant
30
Q

Equation for intrinsic dissolution rate constant

A

K=D/Vh

h is the thickness of the boundary layer

31
Q

What are sink conditions?

A

Solute is removed form the dissolution medium faster than it passes into solution

32
Q

How does Noyes Whitney change for sink conditions?

A

dm/dt= kACs

33
Q

Method for measuring intrinsic dissolution rate?

A

Stationary risk method

34
Q

In the stationary disk method what are kept constant?

A

S.a. Temp, agitation/stirring, pH

35
Q

Stationary risk method does what…how…

A

Measures intrinsic dissolution rate by holding drug pellet 1 inch rotating at 50rpm

36
Q

Five main stages the idea immediate release profile goes through in dissolution

A 
Disintegration
Deaggregation
Release
Occulation - system saturated and becomes non-sink
Occlusion
37
Q

For poorly soluble drugs the dissolution rate may be augmented by…

A

Increasing the disintegration rate and deaggregation

38
Q

What aspects are controlled in controlled release formulations

A

Disintergreation and deaggregation

39
Q

Organoleptic drugs are dealt with by…

A

Unpalatable drugs.
Sweeteners, flavours and perfumes are only for liquid and chewable formulations
Film coated tablets for very unpleasant drugs

40
Q

children and onganoleptic properties

A

Often relate colour to taste

Yellow for lemons

41
Q

Sweeteners often used… 2

A

Sucrose

Sodium saccharine

42
Q

Diabetic sweetener used

A

Sorbital

43
Q

Colour inclusion is complex becuase

A

Banning of traditional colours in some countries and not others

44
Q

Design rights last…. Patent lasts…

A

Design rights such as exact colours 50 years

Patent is only 20 years

45
Q

Commercial drug products should have a shelf life of…..

A

5 years where possible

46
Q

Criteria for drug stability (storage life)

A

Potency should not fall below 90-95%

Should perform as it did when it was first manufactured.

47
Q

Investigations into drug stability should determine 3

A
  • What type of excipient should be applied
  • what protective additives should be used
  • what protective packaging is required? (Amber bottles etc)
48
Q

Trace metals are a problem in storage becuase

A

They can catalyse degredation

49
Q

Hydrolysis occurs due to presence of…4

A

pH

H2O, H3O+, OH-

50
Q

Oxidation occurs due to presence of…

A

O2

51
Q

Photolysis occurs due to

A

Visible and UV light

52
Q

Trace metal catalyst examples

A

Fe2+
Cu2+
Etc

53
Q

Most common 2 pathways causing drug degredation in storage?

A

Hydrolysis and oxidation

54
Q

Methods for avoiding hydrolysis

A

Remove water moisture - desiccant
Lower water activity - add solvents or sugars
Elimination of hygroscopicity - use salt form
Use solid dosage form

55
Q

Simple method of avoiding drug degredation by pH

A

Identify pH min

56
Q

How to avoid drug degradation by temperature

A

Refrigerate at 4Cnu

57
Q

How to avoid light degredation

A

Amber bottle

Medicines design II - solid dosage forms (11 decks)

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