Tablet Coating and Drug Release

Are gastric resistance and enteric coating the same thing?

Yes

What are the 3 types of coating?

• Film coating

• Sugar coating

• Press coating

Why do we coat tablets?

• To protect ingredients from environment (light and moisture)

• Taste masking

• Make the tablet easier to swallow

• Coloured coating allow for rapid identification of product by the pharmacist and the patient

• Film coatings have enteric or controlled release properties

What are the stages of sugar coating a tablet?

• Sealing – prevents water entry (e.g. shellac, CAP)

• Sub-coating – builds size/rounds tablet (CaCO₃ or talc + sucrose)

• Smoothing – smooth surface (sucrose syrup)

• Colouring – adds colour to tablet

• Polishing – gives shine (beeswax, carnauba wax)

• Printing – adds logo or code

What is film coating and how is it applied to tablets?

• Most modern tablets are film coated rather than sugar coated

• Involves spraying a thin polymer film onto the tablet core

• Coating liquid = polymer + solvent + additives (e.g. pigments, plasticisers)

• Forms a thin, uniform layer around the tablet

Sugar coating Vs Film coating

• Film coating is faster

• The weight increase due to film coating is only 2-3%, whereas sugar coating adds like 30-50%

What are the issues with coating?

• Picking/chipping

• Roughness

• Sticking

• Film cracking/peeling

What are drugs enterically coated?

Protects the tablet core from disintegration in the acid environment of the stomach

1. Prevents acid attack on a drug unstable at low pH

2. Protects stomach from the irritant effect of certain drugs

3. Facilitates absorption of a drug that is preferentially absorbed further down the GI tract

4. Taste masking

What is enteric coating?

Coating that is insoluble at low pH (stomach) but dissolves at higher pH (intestine)

• Enteric means intestine

Why are pH-sensitive polymers are used in enteric coating?

pH in the small intestine

• The drug with enteric coating will reach the small intestine

• The polymer in the enteric coating dissolves in specific pH.

• When it reaches the small intestine, the pH is now suitable and the coating will dissolve

Why can’t you eat food when you take an enteric coated drug?

The food raises the pH in the stomach, leading to the drug to be dissolved in the stomach rather than the small intestine where it would be absorbed

Delayed-released tablet

Enteric coated drugs will only be absorbed in the small intestine

• There is a lag time

What are multi-particulate coatings?

• Drug is divided into many small particles (pellets/beads)

• Typically 0.5–2.0 mm diameter

• Can be filled into sachets, capsules, or compressed into tablets

Why are multi-particulates used?

• Easier to swallow

• You can control dosings easier

When are multi-particulate coatings used?

• Controlled release

• Gastro-resistant (enteric) release

• Extended release

• Site-specific drug delivery

What are the advantages of multi-particulates?

• More consistent GI transit than single dose monolithic tablet

• Less likely to suffer from dose dumping

What are the disadvantages of multi-particulates?

• Control of membrane characteristics using film coating can be difficult

• Multi-particulates are difficult to retain in the upper GI tract

What are the types of multi-particulates?

Extruded/spheronized granulates

• Produced in modified granulating equipment

• Drug granulate extruded through a mesh under pressure to form small particles for spheronization

What are the drug release mechanisms from multi-particulates?

• Diffusion: On contact with aqueous fluids of GI tract, water enters interior of particle by diffusion. Dissolution occurs and drug diffuses across controlled release coat.

• Osmosis: In allowing water to enter, osmotic pressure builds up within pellet interior forcing drug solution out.

• Erosion: Some coatings are designed to degrade gradually with time, thereby releasing drug contained within pellet.

What is MUPS?

Multiple-unit pellet systems

• Enteric coated particles are compressed into a tablet

• The polymer coat must be more flexible because of compression forces that are applied in the tabletting process

1. Capsule

2. MUPS

MUPS dissolves faster. It has a smaller particle size.

1. Fasting state. Lower pH

2. Fed state. Higher pH.