D1 Intro to formulation and excipients Flashcards
(91 cards)
1
Q
what do we mean by the term ‘drug’?
A
pharmacologically active ingredient in a medicine
2
Q
what do we mean by the term ‘excipients’?
A
substances which are added to the drug to achieve safe, efficient and convenient medicines and might, for example, control the release of drug from the medicine or increase the size of a tablet to make it suitable to handle
3
Q
what is a drug’s therapeutic window?
A
between the drug concentration for minimal therapeutic effect and that for going into toxic adverse effects
4
Q
why is oral a good route of administration to start with with patients?
A
- non-invasive
- painless
- often associated with improved compliance
- cost-effective manufacturing
- better for children (needles are scary!)
5
Q
what is medicine compliance?
A
the extent to which a patient correctly follows a drug scheme
6
Q
what form do substances have to be in to be transported across biological membranes and what does this allow for?
A
- only substances in the molecularly dispersed form (in solution)
- they are absorbed into the systemic circulation after crossing the biological membrane
7
Q
what must tablets go through in order to be absorbed?
A
- disintegration into granules
- (deaggregation into drug particles)
- dissolution
8
Q
what does the use of a solution route of administration bypass in the absorption process?
A
- providing no precipitation occurs, the solution bypasses dissolution
- there is also no disintegration step as it is not a solid dosage form
9
Q
what is the general order of bioavailability from high to low of suspensions, solutions and solid dosage forms?
A
- not a universal rule
- general rule is:
solutions > suspensions > solid dosage forms
10
Q
what is the dissolution rate of a drug?
A
the rate at which drug particles become individual drug molecules dispersed within a solvent eg. the GI fluids
11
Q
what equation is used to describe the rate of dissolution of drug particles?
A
Noyes-Whitney equation
12
Q
what do we want the dissolution rate to be of drugs numerically? what does this number mean?
A
- a large number
- this means the rate is high and dissolution is fast
13
Q
which values in Noyes-Whitney do we want to be high and which ones low?
A
- numbers on top of fraction to be high:
k, A and (Cs-C) - numbers on bottom of fraction to be small:
h
14
Q
in the Noyes-Whitney equation, what is k?
A
diffusion coefficient (sometimes given the symbol D)
15
Q
in the Noyes-Whitney equation, what is A?
A
surface area
16
Q
in the Noyes-Whitney equation, what is Cs?
A
saturation solubility in diffusion layer
17
Q
in the Noyes-Whitney equation, what is C?
A
concentration of drug in solution
18
Q
in the Noyes-Whitney equation, what is h?
A
thickness of diffusion layer
19
Q
what are the factors affecting dissolution rate of solids in liquids? (components of NW equation)
A
- A: surface area of undissolved solid
- Cs: saturation solubility in diffusion layer
- C: concentration of drug in solution
- k: diffusion coefficient (sometimes has symbol D)
- h: thickness of diffusion layer
20
Q
the surface area of undissolved solid (A) affects the dissolution rate of solids in liquids. what is this factor affected by?
A
- size of particles (smaller particles = bigger surface area)
- porosity of solid particles
21
Q
the saturation solubility in diffusion layer (Cs) affects the dissolution rate of solids in liquids. what is this factor affected by?
A
- temperature
- molecular structure
- crystalline form
- presence of other compounds
22
Q
the concentration of drug in solution (C) affects the dissolution rate of solids in liquids. what is this factor affected by?
A
- volume of dissolution medium (increase V, decrease C)
23
Q
the diffusion coefficient (k, sometimes D) affects the dissolution rate of solids in liquids. what is this factor affected by?
A
viscosity of the medium
24
Q
the thickness of the diffusion layer (h) affects the dissolution rate of solids in liquids. what is this factor affected by?
A
degree of agitation of medium
25
what are the roles of excipients?
- aid preparation of the dosage form
- enhance patient acceptability
- enhance the functioning of the dosage form
26
are excipients inert in medicines?
- they were historically thought to be
- this is now not the case
- excipients can have an impact on bioavailability which can be unintentional and undesirable
27
explain the role of fillers / diluents as excipients. give an example
- increase the bulk volume of powder and makes tablets a suitable size for handling
- eg. lactose (most common)
28
explain the role of disintegrants as excipients. how do they usually work? give an example
- ensures the tablets breaks up into fragments when in contact with a liquid
- usually work by facilitating water uptake or by rupturing the tablet by swelling
- eg. starch and cellulose (very common examples)
29
what component of the Noyes-Whitey equation is increased by disintegrants in medicines?
A (surface area of undissolved solid)
30
explain the role of absorption enhancers as excipients
- modulates permability of a membrane eg. intestinal cell membrane
31
explain the role of binders as excipients. give an example
- ensures granules and tablets have the required mechanical strength
- eg. cellulose and PVP (common)
32
explain the role of dissolution enhancers as excipients. give an example
- temporarily increase solubility during dissolution
- may be required if the drug displays low aqueous solubility (when dissolution may be the rate-limiting step)
- a notable example is the inclusion of a substance which forms a salt with the drug
33
explain the role of glidants as excipients. give an example
- improve the flowability of the powder
- eg. magnesium stearate and talc
34
explain the role of lubricants as excipients. give an example
- ensure the ejection of the tablet from the die cavity can occur with low friction, preventing capping and fragmentation
- eg. magnesium stearate
35
explain the role of matrix formers as excipients
- speed up or slow down the release of drug
- often polymers of lipids
36
which 2 excipients relate strongly to maximising the Noyes-Whitney equation?
dissolution enhancers
disintegrants
37
what are crystalline materials?
those in which the molecules are packed in a defined order, and this same order repeats over and over again throughout the particle
38
what is a polymorph? give an example of a drug and its polymorphs
- many drugs exist in more than one crystalline form and each crystalline form is known as a polymorph
- eg. chloramphenicol palmitate (an antibiotic) exists in 3 polymorphs: stable, metastable, unstable
39
why polymorph of chloramphenicol palmitate is included in dosage forms and why?
- metastable
- the unstable is too unstable for inclusion
- stable is less soluble than metastable and dissolves so slowly that it is virtually ineffective
40
what component of the Noyes-Whitney equation is changed by the polymorph?
Cs (saturation solubility in diffusion layer)
41
what can lead to a much greater degree of ionic dissociation of a weak acid when it dissolves in water? what does this lead to? give an example
- converting the weak acid into its sodium salt leads to greater ionic dissociation
- solubility consequently rises and Cs changes in the Noyes-Whitney equation
eg.
aqueous solubility of salicylic acid is 1 in 550
aqueous solubility of its sodium salt is 1 in 1
42
what is a solution?
homogenous, molecular mixture of 2 or more components
43
what is the fastest acting oral dosage form and what is it limited by?
- solution
- limited only by gastric emptying
44
what form is the drug in in a solution and what does this mean?
- already in a molecular form
- available for absorption
45
what formulation is often used in the neonatal, infant and toddler age groups?
- peroral formulations that are often solution based
- eg. syrups or suspensions
46
possible limitations of solutions
- acidic drugs as salt form can precipitate in the stomach, however, precipitate dissolves easily in the small intestine
- poorly water-soluble acidic drugs may have better bioavailability as a well formulated suspension of free acid
47
give an example of a poorly water-soluble acidic drug that may have a better bioavailability as a well formulated suspension of free acid
Phenytoin
48
describe the composition of suspensions
the solid material (usually the drug) does not dissolve in the vehicle to any appreciable extent
49
why may medicines be formulated as suspensions for oral delivery?
- drugs show limited aqueous solubility related to their target dose and hence an aqueous solution formulation is not feasible
50
which formulation is more efficient, solutions or suspensions?
- solutions, but suspensions are almost as efficient
- typically, poor water-soluble drugs show dissolution rate-limited absorption so all physicochemical factors apply
51
which physicochemical factors apply when considering why poor water-soluble drugs show dissolution rate-limited absorption?
particle size
wetting agents
crystal form
viscosity
52
what does the parenteral route of administration involve and what are the 3 main methods? state 2 more parenteral methods that are used less frequently
- injection of the formulation into the body at various sites
- subcutaneous, intramuscular, intravenous
- intrathecal and intracardiac are used less frequently
53
what route of administration has 100% bioavailability and why?
intravenous, the entire dose is entering the circulation
54
what issues are there with patient acceptance surrounding parenteral drug delivery?
- pain
- inconvenience
55
why may the parenteral route be used for drug delivery despite its issues of pain and inconvenience?
- if drugs are poorly absorbed following oral administration
- when rapid absorption is needed
- if patient is unconscious
56
describe injectables
usually sterile solutions or suspensions
57
is absorption faster from injectable solutions or suspensions and why?
- solutions
- drug is already in the molecularly dispersed form
58
state some common co-solvents in solutions that are delivered by the parenteral route
alcohols such as ethanol and propylene glycol
59
how can oily vehicles be used in injectables and give an example of this use
- to provide a 'depot' of drug for slower absorption because bodily fluids are aqueous
- administered by intramuscular route
- eg. penicillin injections
60
state some common vehicles for intramuscular injections
esters such as ethyl ethanoate and benzyl benzoate
61
what are the functions of other excipients in injections?
- render the preparation isotonic
- adjust the pH
- increase stability
62
what are pessaries?
- vaginal suppositories
- solid, single-dose preparations for vaginal insertion
- can be prepared in various shapes, usually ovoid, with a volume and consistency suitable for insertion into the vagina
63
what do pessaries contain?
one or more active substances dissolved or dispersed in a suitable base that may be soluble or dispersible in water or may melt at body temperature
64
what should the base be in a pessary?
- non-irritating
- physically and chemically stable
- pharmacologically inert
65
why is leakage not likely to be problematic in pessaries?
viscosity of the vehicle after melting or dispersing is high
66
common bases in pessaries
- hydrophobic waxes, fats, witepsols
- hydrophilic waxes, macrogols, PEG
- gelatin (hydrophilic), glycerogelatin
67
what property do hydrophilic bases have and what can they do?
water-miscible and can mix with secretions
68
what does the choice of pessary base depend on?
- drug properties
- there is no single ideal suppository base
69
give an example of a topical / transdermal route of drug delivery
contraceptive patch
70
what are ointments, creams and pastes?
- a drug in a semi-solid base
71
what can the base in ointments, creams and pastes be?
- either hydrophilic or hydrophobic
- this is important because the nature of the base governs release characteristics
72
are ointments hydrophobic or hydrophilic?
hydrophobic
73
composition of creams
semi-solid emulsions
74
why are pastes stiffer in consistency?
contain more solids / powders
75
state some examples of solvents in topical medicines
water
propylene glycol
ethanol
isopropyl alcohol
76
state some examples of solubilising agents in topical medicines
surfactants
eg. sodium lauryl sulphate, cetrimide
77
state some examples of oils in topical medicines
mineral oil
liquid or soft paraffins
silicone oils
78
state some examples of thickening agents in topical medicines
- hydroxypropyl methyl cellulose (HMPC)
- polyvinylpyrrolidone (PVP)
79
state some examples of preservatives in topical medicines
antioxidants
eg. ascorbic acid
antimicrobial agents
eg. parabens
80
state some examples of pH modifiers in topical medicines
lactic acid
81
would the use of a more soluble polymorph maximise or minimise dissolution rate?
maximise
82
would the use of a palmate salt of a weak base maximise or minimise dissolution rate?
minimise
83
would decreasing the particle surface area maximise or minimise dissolution rate?
minimise
84
would the use of the hydrate maximise or minimise dissolution rate?
minimise
85
would the use of a non-aqueous solvate maximise or minimise dissolution rate?
maximise
86
would the use of the amorphous form maximise or minimise dissolution rate?
maximise
87
would the use of a strong acid salt of a weakly basic drug maximise or minimise dissolution rate?
maximise
88
would increasing the particle size maximise or minimise dissolution rate?
minimise
89
would the use of the sodium salt of a weakly acidic drug maximise or minimise dissolution rate?
maximise
90
would increasing the particle surface area maximise or minimise dissolution rate?
maximise
91
would decreasing the particle size maximise or minimise dissolution rate?
maximise
