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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
Replenishment of drug molecules in the diffusion layer is dependent on ...
Rate of diffusion - the whole process is cycli
25
Cycle of something dissolving
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
Dissolution is dependent on rate
Or diffusion of dissolved molecules from sat boundary layer to bulk
27
Quantitative description of diffusion of dissolved solute across the boundary layer....
Noyes-Whitney equation
28
Noyes Whitney equation is
-dm/dt= kA (Cs-Ct)
29
Define all parameters of the Noyes-Whitney equation
``` 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
Equation for intrinsic dissolution rate constant
K=D/Vh h is the thickness of the boundary layer
31
What are sink conditions?
Solute is removed form the dissolution medium faster than it passes into solution
32
How does Noyes Whitney change for sink conditions?
dm/dt= kACs
33
Method for measuring intrinsic dissolution rate?
Stationary risk method
34
In the stationary disk method what are kept constant?
S.a. Temp, agitation/stirring, pH
35
Stationary risk method does what...how...
Measures intrinsic dissolution rate by holding drug pellet 1 inch rotating at 50rpm
36
Five main stages the idea immediate release profile goes through in dissolution
``` Disintegration Deaggregation Release Occulation - system saturated and becomes non-sink Occlusion ```
37
For poorly soluble drugs the dissolution rate may be augmented by...
Increasing the disintegration rate and deaggregation
38
What aspects are controlled in controlled release formulations
Disintergreation and deaggregation
39
Organoleptic drugs are dealt with by...
Unpalatable drugs. Sweeteners, flavours and perfumes are only for liquid and chewable formulations Film coated tablets for very unpleasant drugs
40
children and onganoleptic properties
Often relate colour to taste | Yellow for lemons
41
Sweeteners often used... 2
Sucrose | Sodium saccharine
42
Diabetic sweetener used
Sorbital
43
Colour inclusion is complex becuase
Banning of traditional colours in some countries and not others
44
Design rights last.... Patent lasts...
Design rights such as exact colours 50 years | Patent is only 20 years
45
Commercial drug products should have a shelf life of.....
5 years where possible
46
Criteria for drug stability (storage life)
Potency should not fall below 90-95% | Should perform as it did when it was first manufactured.
47
Investigations into drug stability should determine 3
- What type of excipient should be applied - what protective additives should be used - what protective packaging is required? (Amber bottles etc)
48
Trace metals are a problem in storage becuase
They can catalyse degredation
49
Hydrolysis occurs due to presence of...4
pH | H2O, H3O+, OH-
50
Oxidation occurs due to presence of...
O2
51
Photolysis occurs due to
Visible and UV light
52
Trace metal catalyst examples
Fe2+ Cu2+ Etc
53
Most common 2 pathways causing drug degredation in storage?
Hydrolysis and oxidation
54
Methods for avoiding hydrolysis
Remove water moisture - desiccant Lower water activity - add solvents or sugars Elimination of hygroscopicity - use salt form Use solid dosage form
55
Simple method of avoiding drug degredation by pH
Identify pH min
56
How to avoid drug degradation by temperature
Refrigerate at 4Cnu
57
How to avoid light degredation
Amber bottle

Medicines design II - solid dosage forms (11 decks)

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