Pharmaceutics-Excipients For Film Coating Flashcards
what is coating?
Process by which an essentially dry outer layer of material is applied to a surface.
what are the types of coating?
film coating and sugar coating
what are film coatings for?
-they’re the principal means of coating for immediate and modified release drugs
what are sugar coatings for?
- they’re the traditional means of coating but film-coating is becoming more common now.
- used to mask taste of drugs and the sugar was soluble
what three things does film-coating moderate?
- moisture
- air
- light
what determines the drug release profile?
the solubility and permeability of the coating
what makes a coating safe?
- if it provides product identification
- if it protects the user from the dust of the toxic drug
what does ‘modified drug release’ mean?
-it is when the release of the drug is delayed and/or extended
how do coatings improve drug stability?
- Make product more robust for handling (e.g. less friable).
- Protect product against oxygen, moisture and light.
- Separate incompatible materials.
how does coating influence the usability and user acceptability of the drug?
- improves the ease of swallowing the drug (e.g. smooth, slippery surface)
- improves the organoleptic properties of the drug (e.g. appearance and taste)
what are the three types of drug release and what do they mean?
- Immediate release - rapid drug release
- Delayed release - gastro-resistant or enteric. Coating protects drug from gastric degradation and targets drug release in the intestines
- Extended release - coating promotes sustained release or controlled release of drug (i.e. larger dose of drug released over a prolonged period of time). This is not dependent on pH
If the coating is insoluble in water, what is used?
an organic solvent is used as the coating solution.
why do coatings have low permeability?
- to minimise degradation of core by oxidation, hydrolysis and photolysis.
- Low water permeability for taste masking.
Describe the viscosity of coatings?
- low viscosity for good fluid flow through equipment
- increased viscosity when dissolved or dispersed
what is the typical thickness of film-coatings?
20-100micrometers
why must the film coating had a high tensile strength?
to resist breakage
why should the coating be flexible?
so it can deform and not crack in response to stress
why do coatings include adhesive?
so they can stick and stay on the core material
what are the essential film-coating excipients?
- polymer
- plasticiser
- Solvent
- Colourant
what are the optional excipients for film-coatings?
- wetting agent
2. anti-tack
what is the role of the polymer in the coating?
-the drug is released when the polymer dissolves and/or becomes permeable to water. This is controlled by the substituent groups.
for immediate release drugs, what should the substituents on the polymer be?
soluble (hydrophilic) or basic to ionise in the stomach
for delayed release drugs, what should the substituents on the polymer be?
non-ionied in the stomach but rapidly ionised in intestines
for extended release drugs, what should the substituents on the polymer be?
non-polar for reduced solubility and permeability for slower drug release.
what are semi-synthetic polymers?
- they are polymers derived from cellulose coming from a natural source.
- the cellulose substitutes with the side chains of the polymer
what are synthetic polymers?
they are designed and assembled artificially
what are cellulosics?
cellulose derivatives for immediate, delayed and extended release
what are the characteristics of Cellulose derivatives for immediate release?
- Low molecular weight variants.
- Low degree of hydrophobic methyl (CH3) substitution.
- Abundance of hydrophilic hydroxyl (OH) groups.
- e.g. Methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxylpropyl methyl cellulose (hypromellose).
what are the characteristics of Cellulose derivatives for delayed release?
Phthalate esters of -cellulose derivatives with phthalic acid.
- contain carboxyl groups which Ionise at 5:5.
- e.g. Hydroxypropyl methyl cellulose phthalate, Cellulose acetate phthalate
what are the characteristics of Cellulose derivatives for extended release?
- High molecular weight variants.
- Abundance of hydrophobic alkyl substituents.
- Extensive cross-linking.
- e.g. Ethyl cellulose, cellulose acetate.
what are polymethacrylates?
-they are Methacrylate co-polymers, whose properties depend on the chemistry and ratio of different monomers
what dictates the release profile of polymethacrylates?
Water solubility and lm permeability
For immediate release, what is the solubility of Polymethacrylates?
water soluble in stomach at low pH (acidic conditions)
For delayed release, what is the solubility of Polymethacrylates?
water soluble in intestines at high pH (alkaline conditions)
For extended release, what is the solubility of Polymethacrylates?
insoluble in water, instead swells to become permeable to let water through to dissolve the drug
For immediate release, what is the R group attached to the polymethacrylate?
Amino alkyl
For delayed release, what is the R group attached to the polymethacrylate?
Carboxyl
For extended release, what is the R group attached to the polymethacrylate?
Ester or Ammonioalkyl
what causes swelling in the polymethacryllates for delayed release?
Ionised groups promote swelling by electrostatic repulsion
what are vinyl derivatives useful for?
immediate release
What is the purpose of plasticisers?
To increase flexibility and reduce brittleness
What is the role of bridging molecules?
To mediate intermolecular attraction between polymer chains to allow flexible movement of polymer molecules
Which of the two are water soluble and water insoluble dyes and pigments?
Dye-water soluble
Pigment-water insoluble
What is the purpose of colourants?
- enhance visual appearance
- aid product identification
Why are pigments preferred over dyes?
- Pigments aren’t absorbed
- They’re more photostable
- Have a high opacity
- Possible to optimise coating permeability
- Not susceptible to mottling due to solute migration
Why are setting agents added?
- Reduces surface tension of coating solution/dispersion
2. Enhances surface coverage by coating solution
Why is anti-tack used?
- Prevents adhesion of coating to each other or to other surfaces hence preventing fusion
