Coatings & MR

Question 1

Why is coating tablets beneficial?

Answer 1

protect ingredients from light and moisture

improve organoleptic qualities (taste, smell, mouth feel)

improve swallowing

coloured coatings
- mask changes in colouration of core
- aid identification

improves handling characteristics
- increased mechanical strength and no dusting

functionality

Question 2

What is the ideal coating method?

Answer 2

tablets must comply with pharmacopoeial tests
- should be uniform before and after

avoid abrasions at the edges and crowns

avoid breaking tablets

Question 3

How is sugar coating achieved?

Answer 3

sealing of the core
= with a hydrophobic coat using cellulose acetate phathalate, acrylates or shellac
- to avoid dissolution during coating

subcoating
= uses a mixture of solutions and solids or suspensions like sugar, calcium carbonate, talc, gum acacia
- to smooth out the sharp angles but could increase tablet weight by 50-100%

smoothing
= application of a dilute syrup like titanium or iron oxide
- cover rough surface

polishing
= using beeswax or carnauba wax

printing

Question 4

How is film/spray coating achieved?

Answer 4

it is achieved by spraying an atomised coating solution evenly across a tablet and allowing it to dry
- typically adds 2-3% w/w

• used for organoleptic improvements (taste, smell, mouth feel)
• logos and break lines are distinct
• can be used for sustained release and gastro resistant

Question 5

What is film/spray coating theory?

Answer 5

particles are coated via repeated movement into and out of the spray zone
coat spreads onto and into the particle
particle is then dried and the process is repeated
- aim is to build up an even coat gradually

if sprayed in one go then there is risk of the tablet dissolving and risk of the tablets sticking together

Question 6

What are the main types of methods for film/spray coating?

Answer 6

rotating drum coaters
fluidised bed
- top spray
- bottom spray
- rotating fluidised bed

Question 7

What are coating issues associated with film/spray coating?

Answer 7

coatings may be uneven
- fail uniformity of mass
- patchy coating

coatings can be abrasive
- chipped or broken tablets

inadequate drying
- tablets may stick together

formulation of coating may result in fill cracking or bridging of break lines

Question 8

What is press/compression coating?

Answer 8

a tablet is used as a core for a new tablet
- no solvent required resulting in lower interaction between layers

Question 9

What is enteric coating? What are the uses? What is used for coatings?

Answer 9

coatings which enable drugs to dissolve in the small intestine instead of the stomach
- onset of action is delayed

protects acid labile drugs from the stomach
- omeprazole, pantoprazole

methacrylic acid methacrylate copolymer
cellos acetate phthalate

Question 10

What are the different types of coating?

Answer 10

sugar coating
film/spray coating
press/compression coating

Question 11

What are types of hydrophobic coatings?

Answer 11

shellac with polyvinylpyrrolidone (PVP)
cellulose acetate phthalate
acrylates

Question 12

What are the stages of sugar coating?

Answer 12

sealing of the core
subcoating
smoothing
polishing
printing

Question 13

What are the contents of film/spray coating?

Answer 13

solvent
- usually organic but water can be used

polymer
- celluloses = (HPMC/HPC/MC)
- vinyl polymers
- amino alkyl methacrylate (Eudragit E)

pigments
- insoluble pigments
- soluble dyes

plasticiser
- small molecules and those with low glass transition temperatures
= PEG, glycerol, propylene glycol

Question 14

What is the main benefit of using Eudragit E (amino alkyl methacrylate) for coating?

Answer 14

burst release in the stomach

Question 15

What are the advantages of sustained release formulations?

Answer 15

advantages
- reduced frequency of dosing
= increased compliance, increased activity of API throughout the night, less need for nurses in hospital

• can be used for chronic illnesses with breakthrough issues
  = depression, asthma
• may reduce side effects
  = due to reduced peak plasma concentration
• are patentable dosage forms/intellectual property

Question 16

What are the disadvantages of sustained release formulations?

Answer 16

disadvantages
- costs per unit is higher
-
some API’s are absorbed at a specific point in the GIT
= if missed then no therapeutic effect (riboflavin, ferrous sulphate)

• overdose is not easily solved
• tablets can be very large
  = may lodge in the oesophagus, localised high concentration can cause irritation
• dose dumping or underdosing/poor release

Question 17

What are membrane controlled systems?

Answer 17

drug is contained within a tablet core
tablet is coated with a polymeric material
water diffuses into the core, solubilising the drug causing it to diffuse outward

can be pseudo zero order or (slow) pseudo first order release

Question 18

What is dissolution controlled release?

Answer 18

drug release is determined by the thickness and the dissolution rate of the polymer membrane surrounding the drug core
- once the coated polymer membrane dissolves, the drug will release similarly to an immediate release preparation

multi particulate systems using long chain PEG/PEO

Question 19

What is an osmotic pump system? How must it be set up?

Answer 19

tablet is coated with a semi permeable membrane/coat with an opening/pore
osmotic potential causes water to enter the tablets
the increased pressure forces the API out

size of the orifice/opening must be optimised
- too small = hydrostatic pressure will cause tablet deformation
- too big = solute diffusion may occur directly (dissolution)

semi permeable membrane must be optimised
- thick enough to ensure shape is maintained
- thin enough to ensure movement of solvent