COATINGS of dosage forms Flashcards
What is coating?
Outer layer of coating material applied to the surface of the dosage
Give some reasons for coating an API?
- protecting API from the environment e.g moisture, light temp
- allowing modified release characteristics e.g not in stomach, e/c protection so no breakdown in acidic conditions
- masking taste, swallowing
- Brand identification
- improves product flow, mechanical strength
- reduce the risk of cross-contamination
what are the 3 types of coating, and for each explain the concept
Film coating - deposition of a thin film of polymer based formulation onto surface e.g HPMC - cellulose ether
Sugar - spraying of sucrose based coating to tablet core
Compression coating - compaction of granular material around a pre formed core - good to separate non compatible ingredients
Advantages of using a film coating over a sugar coat?
- adds less volume to the tablet - reduced size - only 20-200 um - thin
- better stability of tablet
- better mechanical strength
- one step process whereas sugar is many steps
Outline the process of sugar coating
Applying a cold solution of sugar, seal tablet cores subcoat smooth colour polish print
What does a polymer film coating suspension contain?
the polymer e.g cellulose ether
- plasticisers e.g PEG, oils
- colourants e.g iron oxide/titanium dioxide
- solvent e.g water (used to be organic solvents)
2 types of film coating you can have?
Immediate release - readily soluble/non functional - really just to achieve something such as identification
Modified release - GR (pH >5-6), or extended release - release consistently over long time
Process of film coating?
Fluidised bed coating: Coating liquid sprayed onto a rotating or fluidised mass of dosage forms
Drying - remove solvent, thin film
What are the requirements for having film coating polymers?
- good solubility - determines behaviour in the GIT and also in the solvent
- low viscosity - otherwise will get stuck in nozzle of spray guns
- Low permeability - taste mask - shouldnt be permeable in mouth, and reduced permeability to O2/moisture, an din modified release it must only be permeable in certain places
- mechanical properties i.e film strength(reduce mechanical stress), adhesion - adhere to tablet, film flexibility to reduce cracking during handling
Polymers for immediate release coatings?
- cellulose ethers e.g HPMC, MC, HPC
- Synthetic polymers e.g poly(N-vinylpyrrolidone) or a co-polymer of PVP and Poly vinyl acetate which is more hydrophilic
Cationic eudragits - aminoalkyl methyacrylate copolymers
What is the composition of aminoalkyl methacrylate polymers eudragits?
N,N - dimethylaminoethyl methacrylate (philic)
Methylmethacrylate (phobic)
Butylmethacrylate (Phobic)
What are 3 types of modified release polymers for coating
- cellulose derivatives e.g ethylcellulose ethocel
- Anionic eudragits - methacrylic acid Co-polymers e.g with either co-methylmethacrylate or co-ethylethacrylate
- Phalate esters - cellulose acetate phalate >6.2
What happens to the anionic eudragits at high pH?
The COOH –> COO- becomes ionised, soluble in water
What are plasticisers and why are they added to coatings formulations?
Most film coat polymers are brittle so they are added to increase film flexibility and reduce residual stresses within the coating during drying - make them softer as reduce Tg
Examples of plasticisers
Polyetheylene glycol, propylene glycol
also diethryl phthalate and triethyl citrate
